If you want an easier garden season, February is the time to set the foundation. Two steps do most of the heavy lifting: getting a soil test and prepping beds without damaging soil structure. Done well, these tasks reduce fertilizer guesswork and improve root growth.
You can do a lot right now that sets you up for success without rushing into two classic mistakes:
1. throwing amendments at the garden without knowing what the soil actually needs, and
2. working soil while it’s still too wet, which can damage structure for the long haul.
So, today on Just Grow Something, I’m walking you through what a soil test can (and can’t) tell you, exactly how to collect a sample that’s representative of your whole garden, the key parts of a soil report that matter most for vegetables, and bed prep steps you can do now that improve soil instead of compacting it.
Let’s dig in!
Resources:
My Seed to Sprout course is waiting for you here: https://justgrowsomething.com/indoor-seed-starting
My free Seed Starting eBook is here: https://justgrowsomethingpodcast.com/seedbook
Soil amendment episodes and articles: https://justgrowsomethingpodcast.com/search/amendments
How to calculate how much fertilizer to add to the garden: https://justgrowsomethingpodcast.com/blog/how-much-fertilizer-to-add-to-your-garden
References:
How temperature affects the rate of nitrification: https://livetoplant.com/how-temperature-influences-the-rate-of-nitrification/
Guide to Collecting Soil Samples - Oregon State University: https://extension.oregonstate.edu/catalog/ec-628-guide-collecting-soil-samples-farms-gardens
Soil Compaction from Wet Soils - Purdue University Extension: https://www.purdue.edu/hla/sites/yardandgarden/resist-the-urge-to-work-wet-soil/
Add Organic Matter to Improve Most Garden Soils - Oregon State University: https://extension.oregonstate.edu/news/add-organic-matter-improve-most-garden-soils
Just Grow Something: https://justgrowsomething.com
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Just Grow Something Gardening Friends Facebook Group: https://www.facebook.com/share/g/18YgHveF5P/
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00:00:00
All right, my gardening friends, today we are tackling a topic
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that can sometimes quietly determine how easy or how
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frustrating our whole season is going to be.
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Soil testing and bed prep. And February is the perfect time
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for this because you can do a lot right now that sets you up
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for success without rushing into two classic mistakes, throwing
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amendments at the garden without knowing what the soil actually
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needs and working the soil when it's too wet, which can damage
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structure for the long haul. Welcome back to Just Grow
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Something. I'm Karen Velez, your friend in
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the garden. And today I am walking you
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through the sciency goodness of what a soil test can and can't
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tell you exactly how to collect a sample that's actually
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representative of your whole garden.
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The key parts of a soil report that matter most for vegetables
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and bed prep steps that you can do now that improve soil instead
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of compacting it. Let's dig in.
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OK so soil testing what is it and what does it tell you?
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Why is it worth it? A lab soil test gives you
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information about your soils, nutrient status and its pH so
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that you can select the right fertilizer or amendments to make
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changes or improvements. Without an analysis, it is
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nearly impossible to know what your soil needs for good crop
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growth until it's late and your plants are already showing signs
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of deficiencies or toxicities. A standard university extension
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soil test commonly includes things like pH and the major
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nutrients like phosphorus, potassium, calcium, magnesium.
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Plus, it's likely going to tell you the level of organic matter
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that is in your soil and some other related measurements that
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are used for developing like lime and fertilizer
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recommendations. Essentially, if you take a test
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and you send it to your extension or another outside
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soil service and tell them that you are growing vegetables,
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they're going to look at what looks good and they're going to
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tell you what needs help and how much fertilizer to add to fix
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the problem. In a nutshell, OK, now if you
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choose an off the shelf version, you will be limited to pH and
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the big three nutrients, nitrogen, phosphorus and
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potassium. And if you're deficient in any
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of those things or you need to adjust your pH level, you'll be
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on your own to figure out how much of what to add to make the
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changes that you need to make. It's for this reason that I
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recommend getting an outside test done at least once.
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If you do the off the shelf test every year after that, at least
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you have a good foundation to work from.
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But if you're determined to DIY it, I will link to multiple blog
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articles and podcast episodes that will guide you in what to
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use to amend and when and how. All of that aside, here's the
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practical point. A soil test helps you avoid
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unnecessary applications, and this is especially true when you
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are trying to adjust the pH. I have seen helpful advice and
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I'm using air bunnies here in Facebook groups of people
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recommending someone lime their garden soil without a test just
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because they posted a picture of a plant that looked like maybe
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the pH was too high. But a lot of garden soils are
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already near neutral and unnecessary lime can reduce
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nutrient availability which would make the problem in the
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picture even worse. That's just one example, but
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what it boils down to is soil tests help you spend money where
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it matters and skip what doesn't.
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So you can collect soil samples pretty much any time of the
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year, but timing effects how interpretable the results are.
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PH and phosphorus are relatively stable unless you have recently
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applied lime or fertilizer or compost or manure, so it's best
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not to sample immediately after you have done any of those
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applications. If you're prepping for spring
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vegetables, the main goal is lead time, especially for pH
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correction. A lot of amendments work best
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when they have had time to react in the soil, so earlier is
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generally better than later. However, the one nutrient that
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is really affected by the time of year is nitrogen.
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The temperature of the soil greatly affects the availability
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of nitrogen. Nitrification is a critical
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process in the nitrogen cycle, involving the biological
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oxidation of ammonia into nitrite and then subsequently
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into nitrate. This transformation is primarily
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carried out by specialized groups of microorganisms in our
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soil, and factors such as temperature influence this rate
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of nitrification. Nitrification occurs in two main
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steps. The 1st is ammonia oxidation.
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This is where ammonia is converted into nitrite by
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ammonia oxidizing microorganisms.
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The second is nitrite oxidation. That nitrite is then converted
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into nitrate by nitrite oxidizing bacteria.
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The end product, nitrate, is the form that is readily taken up by
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our plants. So why does the soil temperature
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matter? Because microbial activity is
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temperature dependent, both in terms of the enzymatic reactions
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and the overall microbial metabolism, temperature effects,
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nutrient uptake rates, respiration and replication
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rates in those microbes. The ideal temperature range for
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microbial growth and enzyme functions, and therefore
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nitrification rates, is between 20 and 30 Celsius or 68 and
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86°F. Above 35 Celsius or 95
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Fahrenheit, we start to see enzyme structures being damaged
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and microbial cells being damaged or dying off.
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Below 20 Celsius, or 50 Fahrenheit, we see microbial
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rates and enzyme reactions decrease dramatically, and the
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rate of ammonia oxidation drops sharply, often limiting the
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availability of nitrate for plant uptake.
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In other words, if it's too hot or too cold, the microbes can't
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function well enough to do their jobs, which means even if there
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is enough nitrogen in the soil for plant growth, they can't
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make it available to the plants or even to our tests.
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So if we're trying to test for nitrogen availability, we need
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to be testing at the right temperature range, which is
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actually why many university extensions don't even include
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nitrogen levels in their test results for home gardeners.
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It's just too dependent on temperature and moisture
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availability and other factors. So if you can wait to do the
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soil test until your soil temperatures get above 50°F,
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then you'll have a better representation of what will be
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available in your soil during the growing season in terms of
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nitrogen. This is just one more reason why
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we should be doing these testings and amendments in the
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fall rather than in the spring. But if now is the only time we
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can do this and we see that we're deficient, will need to
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choose fast acting amendments. If you have never done a soil
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test before, you might decide to do one right now for all the
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other nutrients and then do one again in the spring just to
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check your nitrogen. The sooner that you can amend
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the better. And there are plenty of fast
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acting nitrogen amendments out there that can be added last
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minute. But there are fewer fast acting
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versions of the other nutrients. So I guess it's test early and
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test often. So how do we collect a good soil
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sample? This is where most tests
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actually go wrong. A good soil test starts with a
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good sample. The first part of this is to
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make sure that you are sampling different areas separately.
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So a lawn and a vegetable garden should be sampled separately,
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and areas with different management history should also
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be split up. So if you have multiple
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vegetable planting areas and one had a bunch of compost worked
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into it last year, but the other one hasn't been amended at all,
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then you're going to want to keep those samples separate
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rather than combining them. If you use raised beds, we want
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to be sampling in the bed where the crop will be planted.
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So in raised beds you want to take the sample from in the bed,
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not from anywhere in the path. Same thing for your in ground
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beds. You're not going to be taking
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pathway measurements. You're you're taking
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measurements and samples from within the areas where you're
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actually planting the crops. You also want to make sure that
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you are taking enough sub samples to make it
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representative. So we want 15 to 20 sub samples
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within a sampling area and then we want to combine them.
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So what does this mean? It means don't take a scoop of
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soil from one spot in your main garden and only test that.
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Walk around in the main garden area and take a bunch of little
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samples, 15 to 20 of them and mix them all together.
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This is going to provide you with an average of your
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conditions in that area, not just the specifics for one
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little spot that you dugout. And again if you have multiple
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areas that you plant in then you may want to run multiple tests
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and you should be taking enough sub samples from each of those
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areas to do that testing. You also want to be sure that
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you are sampling to the correct depth and that you're doing this
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consistently. So for most annual crops,
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sampling is typically from the surface down to about 6 inches
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or so or down to the depth of tillage.
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If you routinely till your garden every year, I like to hit
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right at about the 2 to 4 inch mark because that's generally
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where the large proportion of our plant roots are and where a
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lot of the new the nutrition is going to be coming from.
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The key to this is consistency over time.
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So if you took a soil sample last year, be sure that you are
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taking the samples this year at the same depth.
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We want to compare apples to apples essentially.
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Another thing that's important is to avoid contamination.
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So clean tools matter. Even small amounts of fertilizer
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or amendment residues can contaminate a sample and you may
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end up that you're deficient in something but you don't know it
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because your your test isn't going to show it and then you're
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not going to be correcting the problem as a result.
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You also want to avoid including like mulch or any kind of
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vegetation in the sample at all and then just make sure that you
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are mixing it thoroughly in a clean container.
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We want to combine all those substantial samples and mix them
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in a clean container container before we add them to the bag
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that we're sending in. Again, we don't want any cross
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contamination that could skew the results if you do just those
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steps right. Sample different areas
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separately. Make sure you're sampling in the
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planting beds. Take enough sub samples so that
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it is very representative of the entire garden space.
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Sample it at the correct depth and do that consistently.
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Avoid contamination and make sure that you are mixing the
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sample thoroughly before putting it in the bag you'll be sending
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in. Then you are far more likely to
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reflect the reality in your garden.
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OK, so how do I read this report once we get it back?
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Now, if you're doing an off the shelf test, there are going to
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be instructions on the back of that test that are going to show
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you what each one of those tests mean.
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The pH, the nitrogen, the phosphorus and the potassium.
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There's going to be a color guide for you to be able to
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compare and make your own assessment of whether or not you
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are deficient in any of those or if you have a toxicity like too
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much of something in any of those or if hey, you know it,
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you're doing OK. When it comes to a lab result,
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we're just going to kind of keep this simple and very vegetable
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focus. The first thing that you're
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going to get is the soil pH and the pH effects.
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Nutrient availability. Nutrients are most available in
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a moderately acidic to like near neutral pH.
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Most vegetables perform best roughly in the 5.5 to 7 point O
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range. So ideally that's the soil pH
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that we're looking for. If you do a university soil test
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or one that you send off to a soil service of some sort, they
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will tell you how many pounds of sulfur or lime that you need to
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use in that soil to adjust your pH up or down if needed.
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Again, if you do an off the shelf kit, you are on your own
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to figure that out. I will put some links to my
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rather sciency episodes on this. The next thing is the nutrient
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ratings and recommendations. The mailed reports will
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generally give you a report of what the nutrient levels are in
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the sample that you sent, along with recommendations on how much
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of that nutrient to add to bring it into sufficient levels.
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If you're currently deficient. These mailed reports will also
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often include a rating system that helps you predict whether
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adding a nutrient is likely to increase your yield, which is
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super useful for deciding what actually needs your attention
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and what would just be wasted money essentially.
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Again, off the shelf. You're going to need to do some
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calculating to figure it out. The bottom line is basically if
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you mail a test, follow the lab's recommendations.
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If you do your own, look up how to make the adjustments and
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avoid guessing at amendments. OK, now let's talk bed prep
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because soil testing is step one, But the condition of the
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soil structure depends how well the roots of those plants are
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going to grow. And rule #1 is don't work wet
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soil. OK, if you squeeze a handful of
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your garden soil and it crumbles, you're good to go.
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If it forms a muddy ball, then we need to wait.
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Working it wet is going to increase that compaction risk.
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This is why when we talk about garden planning, I always want
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to make sure that you have a buffer around the dates that you
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choose to transplant or start your seeds out in the garden.
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If you decide that you have a very specific date in mind and
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you need to get those plants in on that date, and you don't
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allow yourself some leeway before or after that date, what
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ends up happening is you feel that pressure to get those
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plants in the ground. And you might do it when the
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conditions of the soil are not ideal.
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And not only can this harm the soil, it can also harm your
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transplants. If your climate is cold and wet
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right now, your best bed prep may be just patients, right?
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Plus a little bit of surface based work like planning and
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gathering your materials and waiting for proper moisture,
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whatever. OK, another thing that is
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important is organic matter and compost, which is very useful,
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but it needs to be intentional. Adding organic matter improves
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the workability of the soil. It helps to loosen clay soil if
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you have it, it helps sandy soil to hold water, and it adds
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nutrients. In other words, compost is super
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useful for more than just adding nutrients.
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In fact, nutrient availability is probably the least important
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function of compost. So once your soil is workable,
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if you didn't do anything at the end of last season, now is the
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time to incorporate about two to four inches of organic matter
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and turn it under. Now, I'm not necessarily telling
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you to till because tillage can destroy soil structure and the
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microbes that we rely on for nutrient availability.
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It also exposes weed seeds and it's going to dry the soil
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faster. But you need that organic matter
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to be worked in if you're adding it in the spring.
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So the rule of thumb is if you add 2 inches of material, turn
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it 2 inches under. If you add 4 inches, turn it 4
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inches under. It needs to start getting broken
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down by those microbes. And the best way to do that is
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to incorporate it in with the microbes into your existing
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soil. This is why the most effective
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way to do this is to just layer it on top of the bed in the late
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fall and cover it with an organic mulch to just sit there
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and break down all winter. Like not only do you avoid
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having to work in cold soil, but then you don't have to turn it
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under, which preserves the soil structure, blah blah blah,
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right? But admittedly, even I can't get
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to all the beds that need to be worked in the late fall and
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sometimes we are just burnt out and we don't want anything to do
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with the garden. So I will be right there
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alongside you amending some of my beds in the spring.
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We do what we can, when we can, right?
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So for gardeners, 2 common approaches both work, right?
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What matters is timing and restraint.
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It's either minimal disturbance, which is top dressing with the
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compost and the mulch. This is to avoid overtilling, or
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you'd kind of do that conventional incorporation where
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you incorporate the compost when the soil is moist, not wet, and
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avoid repeated passes of a tiller or anything like that.
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OK, so here is your late February garden win.
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Take a clean and representative soil sample.
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Get the soil test done and let your results tell you what to
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do. Then prep the beds in a way that
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your soil will thank you for. Don't work it wet, add organic
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matter thoughtfully and choose the disturbance level that
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matches your system. So test first, then prep.
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And remember, if you are starting seeds indoors this
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season and you want a step by step system for indoor seed
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starting, it is not too late to take my seed to sprout course.
00:18:28
From choosing a setup to timing, lighting, soils, containers and
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more. It is quick, it is practical,
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and you can find it at justgrowsomething.com/courses
00:18:38
and I will leave a link to that in the show notes.
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Until next time, my garden friends, keep on cultivating
00:18:43
that dream garden, and we'll talk again soon.