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Today is a clinic episode. A seedling troubleshooting
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clinic, to be exact. Because if you're starting seeds
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indoors, something is eventually going to look weird.
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A tray that was perfect yesterday may suddenly be
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leaning. Something might be looking fuzzy
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on the soil surface, or a seedling that seemed just fine
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just flops over. Here's the good news.
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Most seedling problems come from a small handful of causes.
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Causes that we can actually control light, temperature,
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water, airflow, or sanitation. And once you know what you're
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looking at, you can usually fix it really quickly, or at least
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stop it from spreading to the rest of your tray or happening
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again if you caught it too late. So I'm going to give you a
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simple diagnostic checklist and then we'll walk through the most
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common healing symptoms and what to do about each one.
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Welcome back to Just Grow Something.
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I'm Karen Velez, farmer, horticulturist, plant nerd, and
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I am taking the guesswork out of growing your own food with
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practical research backed steps that work in real life.
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As always with today's episode, I will include resources in the
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show notes for diagnosing seedling problems so that you
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can go as deep as you want later on.
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All right, clinic is open. Let's dig in.
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So before we talk fixes to your seedling problems, we need to
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diagnose. When you see a problem going on
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in your seed starting area, I encourage you to pause and run
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these six questions. Question number one, what stage
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are we in? Are we pre germination?
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Are these newly sprouted plants with just their first cod
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leadens their seed leaves or do we have true leaves already on
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the plant? This matter because the usual
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suspects are going to change depending on the stage of plant
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growth. Question 2 would be is it
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happening in one cell or one container or is it happening to
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the whole tray? One or two cells often points to
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either a problem with seed quality or maybe planting depth
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or just a localized watering issue.
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An entire tray, however, usually points to something in the
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environment, so either the light or temperature or watering
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patterns are off, or a disease that is favored by those
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conditions. Question #3 is it fast or slow?
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Is what happens to your seedlings happening very, very
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quickly, or is it taking some time?
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So if seedlings collapse like in 24 to 48 hours, then we might be
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thinking this is a disease or maybe a severe water or oxygen
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stress. But if it's slowly getting worse
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over a week or two, then we're probably leaning more towards a
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light issue or a problem with nutrition or chronic watering
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issues. Question 4 is what's the light
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setup? Be specific.
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Are your plants in a window? Is it supplemented with grow
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lights? Is it only grow lights?
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How many hours of lights are they getting per day?
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How close are the lights to the seedlings?
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Natural window light is often not enough for really sturdy
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ceilings, and low light is a major driver of stretching, So
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if this is what you're seeing, it likely might be part of the
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light problem. Question 5.
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What's the temperature, Especially after germination?
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A lot of gardeners are going to keep their seedlings too warm
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after they sprout, so warmer than recommended temperatures
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for growing on your plants after they sprout can actually
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contribute to spindly growth and some other issues.
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And then question 6 would be how wet is the seed starting mix or
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your potting mix and how's the air flow?
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So moist and wet are not the same thing.
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Seedlings need water, yes, but they also need oxygen at the
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root zone. So if your seed starting mix or
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your potting mix stays saturated, the roots are going
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to struggle and that also increases your disease risk.
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Also, if a humidity Dome is still on after germination, that
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can trap moisture and reduce the airflow.
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So we really do recommend removing domes once a
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substantial portion of your seeds have germinated and then
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using some gentle airflow to deter fungal problems.
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So keep those six questions sort of in your back pocket.
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And now we're going to tackle the most common problems.
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So the first problem we might see in our seed starting area is
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seeds that aren't germinating at all or germination is very
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uneven. So if the seeds aren't popping
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or only a few cells germinate, then I want you to sort of think
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in this order. The first thing would be the
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temperature. Most garden seeds germinate with
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a soil temperature around 65 to 75 Fahrenheit.
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Some of them like it warmer. There are some cool season crops
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that can start when it's much colder.
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But if your seed starting space is chilly, a heat mat can help a
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lot with this. It will raise the temperature at
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the soil level by anywhere from 5 to 10°F.
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You know, if you're worried about this, you can pair it with
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a thermostat so that you're not overheating the mix and not like
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cooking the seedlings. But This is why we have seedling
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seedling heat mats that are specific to starting seeds.
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And we're not using something like, you know, a heating pad we
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would use for us, right? So temperature could be your #1
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hidden issue in terms of it's not germinating or the
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germination being uneven. The second might be moisture and
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oxygen. Again, seeds do need consistent
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moisture, but a waterlogged mix is going to limit the oxygen and
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actually encourage rot. We don't want seeds sitting in
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water consistently. The goal is evenly moist, not
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swampy. Your third concern might be
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planting depth. A very simple rule of thumb is
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to plant the seeds about twice the width of the seeds.
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So if you your seed packet doesn't tell you how deep you
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should be planting, that is a really good rule to go by.
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If you put the seeds down too deep, that is going to slow the
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emergence and it's also going to increase the stress of that
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little plant as it's trying to pop out of its seed coating.
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If you plant too shallow, then that seedling can dry out or the
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seed itself can dry out and it won't end up germinating.
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So we really want to go for like a happy medium there.
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Twice the width of the seed is the general rule of thumb.
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And then the fourth thing would be the seed quality and its
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storage. I mean, old seed or seed that
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has been stored where it's really warm or really, really
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humid sometimes is going to be less reliable.
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So if one variety that you planted sort of fails to
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germinate or doesn't germinate very well while the others are
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thriving under the same condition, then I would suspect
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that it's an issue with the seed.
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So if you think temperature is the culprit, then adjust the
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warmth at the mix level, not just the room.
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If you think moisture is the culprit, then we want to do sort
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of the same thing that we do with our plants.
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We want less frequent, more thorough watering.
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So we want to water thoroughly and then allow that surface to
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dry out before we water again. Problem #2 would be leggy,
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stretched or leaning seedlings. Leggy seedlings.
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These are the seedlings that are really tall and really thin and
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sort of leaning over. These are one of the most common
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seed starting frustrations and the most common cause of this is
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insufficient light. So low light is the driver of
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seedlings just sort of trying to stretch towards the light and
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that causes the stems to weaken and then of course the plant is
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going to struggle to support itself.
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So in order to have enough light, oftentimes we are going
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to need some supplemental lighting.
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Windows are going to rarely provide enough intensity or
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light duration to really get nice stocky ceilings.
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If you're going to use supplemental light, then you
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want the seedlings about a couple of inches beneath those
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fixtures, so 2 inches difference between the top of the plant and
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the light. So you're going to have to
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continue to raise the light up as those seeds or those
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seedlings get taller. And we want to provide sometimes
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as much as 12 hours of daylight on up to even 16 hours per day.
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And then after your seedlings germinate, we want to avoid
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keeping them very warm because those higher temperatures can
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actually contribute to that spindly growth.
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So once everything in your tray has started to sprout or the
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majority of them have sprouted, then make sure that you are
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removing them off of any heat mat and that will help prevent
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them from getting too hot. But you also have to look too at
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your your air temperatures. Also, a lot of times they like
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to grow in cooler temperatures than what they sprouted in.
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So if your seedlings are leggy, you want to move the lights
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closer. We don't want them to scorch the
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foliage, so don't make them touching, but a couple of inches
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off of the foliage is good. We want to increase the duration
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of the light so it's a consistent more day length, so
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12 hours or so on up to 16. We want to drop the post
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germination temperature just a little bit.
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A lot of these veggies are going to do better with cooler nights
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and more moderate days after sprouting.
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And then add some gentle airflow.
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A little fan is perfect for in your seat starting area.
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We're not trying to create like a wind tunnel or anything, but
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we want some intermittent airflow.
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So I will generally use an oscillating fan just to kind of
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simulate what they would experience if they were outside.
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And that's going to help those seedlings grow more sturdy.
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Problem #3 seedlings collapsing at the soil line.
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So if your seedling looks fine and then suddenly the next day
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it has completely fallen over, especially if you see a very
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thin, pinched or rotted looking stem right at the soil surface,
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this is damping off disease. This is caused by a fungus or a
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fungus like Organism that thrives in cool wet conditions
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and it is most common in very young seedlings.
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So the risk of damping off happens when the surface is very
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damp and there is low light. You might have high salt content
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for if you've been fertilizing your seedlings, which you
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probably don't need to be doing yet at this stage.
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And very cool soil temperatures all associated with increased
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problem from damping off disease.
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And with with damping off, really it is all about
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prevention because once seedlings collapse, that's it,
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they're done, they are not going to recover.
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So your goal is to prevent this from happening.
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And if you see this happening, your goal is to prevent it from
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spreading and you want to sort of reset those conditions.
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So the number one thing here is if you have had damping off in
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seasons before and you reuse your trays, you likely are going
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to want to sort of clean and disinfect those trays or
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whatever your seed starting materials are.
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So you're going to wash off all of your soil and stuff and then
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sanitize the containers in a 10% bleach solution and then just
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let them air dry? I am not a huge stickler for
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this type of sanitation. Just as a matter of routine.
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If you haven't seen problems, then I'm not so worried about
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it, right? If you really want to be sure
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that you're preventing problems, then yes, absolutely you would
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do this every single year. But if you have seen damping off
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or anything else, then this is the first.
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Your first line of defense is to sanitize those trays at the end
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of the season before using them again next year.
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Your second thing would be to make sure that you are using a
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clean, fast draining seed starting medium.
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We never want to use garden soil indoors.
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It is too dense. It can carry pathogens, not to
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mention weed seeds. If you use a regular potting
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soil soil, that's fine so long as it is fine enough to be able
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to drain really, really well. And there aren't that many
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potting soils out there, regular potting soils that I would ever
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recommend for seed starting. The pro mix that I use is one
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that I would absolutely recommend.
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Other than that, you might be better off using a soil less
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medium that just drains very, very well.
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We're trying to avoid that excess moisture, and these
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pathogens thrive when it is cool and wet.
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So we want to keep that mix moist, but we don't want it
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saturated all the time. And so we want to make sure that
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if we're using humidity domes to help sprout things, that we want
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to remove those domes after a substantial portion of those
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seeds have germinated. And then again, use some gentle
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airflow because not only is that good for the seedlings, but it
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also helps to dry that soil surface and that is going to
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deter that fungal growth. The other thing too with air
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movement is we want to sort of avoid overcrowding the
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seedlings, right? So not only are they not going
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to get as good of air movement if they're too close together,
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but that also is going to reduce the light exposure when they are
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crowded. So, you know, you're reducing
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airflow, you're increasing those favorable conditions for
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dampening off, not dampening, damping, damping off.
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And so, you know, if you've got some really dense plantings, you
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might need to thin those out just to prevent damping off from
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happening. So stop if you see it happen,
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right? If you suspect that damping off
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is starting, stop over watering immediately.
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Let everything dry out really, really well.
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Increase your spacing in your airflow.
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Remove and get rid of any of the plants that were affected in the
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cells that they were in. And if it's widespread, then
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make sure that you sort of, you know, make sure that you are
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sanitizing your equipment and you might have to actually
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restart if you starting to lose all your seedlings, start over
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again, sanitize that equipment, get some fresh medium and plant
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again. Problem #4 would be yellowing,
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pale, scorched or spotted leaves.
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This category can be really tricky because multiple
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stressors can look very similar to each other.
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But we can still troubleshoot this logically and we want to
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start with the basics and that is water and roots, uneven
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watering or over watering or extreme drying out, right?
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These are very common sealing problems.
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And so the goal is to supply the plant roots with water and
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oxygen. So we don't want overly
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saturated containers because that can actually stop root
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growth and favor pathogens. And any one of those things can
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cause a description that I just talked about yellowing leaves or
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pale or scorched or spotted leaves, right?
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So you know the same thing with our seedlings, the less
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frequent, more thorough waterings.
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If you are somebody who prefers to bottom water your seedlings
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because it seems like the plants will just take up what they
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need, that's fine. But that water should not be
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sitting in that bottom container at all times.
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That is too much water. So as soon as the soil surface
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is damp, you can see that it's taken up enough water.
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You need to be dumping those trays and not let that water sit
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there and not add any more water back into those trays until
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again, the soil surface is dry. So it doesn't matter if you're
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watering from the top or you're watering from the bottom, the
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condition should be the same. The next thing is to carefully
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consider your nutrition. Many potting mixes contain
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enough fertility to carry seedlings for about 5 to 6
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weeks. This depends on what it is that
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you're using. If you're growing seedlings for
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longer than that, or if you are using a soilless medium that
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does not contain any fertilizers, then you may need
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to use a soilable fertilizer of some sort to feed your
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seedlings. But young seedlings are very
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easily damaged by too much fertilizer.
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So my recommendation is whatever your normal consistency is or
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your normal ratio is that you use for your fertilizer, do half
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that with your seedlings. So 50% of what you would
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normally use if you were using it for a regular plant outdoors
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just to get them through until they're getting ready to be
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transplanted outside. So if your leaves are pale and
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your growth is sort of stalled and the seedlings are older than
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a month, then consider a a light feeding of some sort.
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And then problem #5 would be moldy surfaces or fungus gnats
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or seedlings that don't survive when you finally put them
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outside. This is sort of a rapid fire
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little thing here. So if you're seeing like white
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or silvery growth on the soil surface of your plants, this is
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commonly an indicator of overly wet growth medium.
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Same thing goes if you're seeing sort of a green fungus that's
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growing across. This may not be instantly
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harmful, but it does signal that conditions may be right for
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damping off risk. So you likely want to adjust
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your watering at that point and increase the air movement a
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little bit if you're getting fungus gnats.
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These guys thrive in constantly moist media.
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Again, we want to let the surface dry more between the
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waterings. You can also with fungus gnats
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use yellow sticky traps so that you can monitor and capture the
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adults. There are some extension
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resources that talk about using BTI as an option for like larvae
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management when you use it according to the directions.
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I prefer just to water with a solution of hydrogen peroxide
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and water to kind of get take care of the egg situation in the
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soil if I ever have them. But ever since I really started
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paying attention to my watering practices and making sure that
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that moist that that that media was not moist all the time, I
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have not had a fungus gnat problem.
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And my seed starting area, I mean, I grow thousands of plants
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every year and I don't have a problem with fungus gnats
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anymore. So that would be my
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recommendation. Really start with letting the
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surface dry out and then go on from there.
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And then if your seedlings are having problems when you get
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them outside, that is 100% a hardening off problem.
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If you managed to get your seedlings growing and they
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looked nice and healthy when they were inside, and then you
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got them out into the garden and all of a sudden they died, that
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means they got too much sun or too much wind or a temperature
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swing way too fast. The hardening off process should
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take you about 7 days, sometimes as long as 10 days, starting
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with short periods outdoors, like in the shade and then
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gradually increasing the time and the sun exposure while still
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being protected from major wind gusts until they finally sort of
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are acclimated to being outdoors before you put them out in their
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final place. Another thing that I recommend
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with this is also backing off of the amount of water that they
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get during that seven day period.
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So they've gotten used to being sort of pampered in their little
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seed starting area, right? And now you got to put them out
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into the harsh world of the actual garden.
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And they need to be prepared for that.
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And you're not going to be hovering over them every single
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day, giving them water as soon as the soil surface dries out.
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I mean, if you are, then we have to have another conversation,
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OK. But you know, that should be
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part of your hardening off process is backing off how
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frequently you're giving them water to get them used to those
00:20:00
conditions out in the garden. So if you take nothing else from
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today's seedling troubleshooting clinic, then take this.
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Most seedling problems are not true mysteries.
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They are predictable outcomes of light, temperature, moisture,
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airflow or sanitation. And once you adjust those
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things, then your seedlings are usually turn around really
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quickly. And if you didn't get to them in
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time, at least you can know how to prevent it from happening
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again next time. If you want a step by step
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system for indoor seed starting from choosing a setup to timing
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to lighting to keeping seedlings healthy all the way to
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transplant day, my Seed to Sprout course is built exactly
00:20:50
for that. It is quick, it is practical,
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and it is designed to prevent the problems that we talked
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about today before they even start.
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You can find it at justgrowsomething.com/courses or
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I will also leave a link to that in the show notes.
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Until next time, my gardening friends, keep on cultivating
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that dream garden, and we'll talk again soon.