Gardening is an exercise in improvisation, forcing you to work with soil that’s probably less than ideal to grow plants that may have very specific nutritional requirements. How do you know when your garden’s ready to grow plants?
Soil Testing 101
There are two ways to do a soil test, you can either buy a soil testing kit from a local home improvement store or you can connect with the local university extension office. A rapid test (the home test) can give you a lot of information to start with, but if it detects serious problems, you’ll need to resample and have the extension run it. The cost is typically minimal and the information they’ll provide can guide your amendment decisions.
It’s your call — doing a rapid test is a great way to get an idea about what’s up in the garden, but an extension test will give you deep level details. Their tests are designed for agriculture, but that doesn’t mean they won’t work for your future blueberry patch.
Either way you choose, you’ll have to take some samples. Using a proper soil core sampling probe (or you can wing it with a pointy hand trowel), dig into the soil about eight inches, then bring up your first sample. You only need a bit, but it’s a good idea to keep each sample roughly the same size. When you’re done, you should mix all the soil together to create a combined sample (several plugs from across the whole area you’re trying to plant).
If you’re using a home test, you’ll get the basic information you really need to start. Your home soil test kit should contain these four tests, minimum:
pH. Some plants like acidic soil, others like alkaline. Obviously, you can’t plant the two types in the same garden, since it’s impossible to create both conditions at once. Many gardeners choose plants based on the pH of the soil, rather than trying to alter the soil to fit their plants of choice. The first option is way easier in the long term.
Nitrogen (N). Nitrogen is one of the most important nutrients for most plants. It’s a major component of chlorophyll, the green substance that allows plants to make their own food. In general, more nitrogen is better than less, but there’s a limit on that. Too much of a good thing will cause your plants to grow rapidly, putting out a lot of leaves at the expense of flowers and fruit. Many overly-nitrogened plants will get “leggy,” that is to say that they’re taller, thinner and more frail than they should be.
There’s one exception to the “more is better” philosophy of nitrogen. If you’re planting legumes, either ornamental or edible, low nitrogen levels aren’t a problem. They have structures on their roots that harbor nitrogen-producing bacteria, so they’ve basically brought their own nitrogen to the party. If you turn annual or edible legumes back into the garden before they die naturally, you can also improve the nitrogen levels of the soil over time.
Phosphorus (P). Phosphorus helps plants mature, as well as being vital to flower and fruit production. Without sufficient phosphorus, your plants will be stunted, they may have a purple cast and they’re definitely going to be a serious let down. It’s difficult to get too much phosphorus in your soil, though. In fact, top dressing your plants with a little extra phosphorus can really get them going in the spring.
Potassium (K). Did you know that plants breathe? Well, they release oxygen regularly through openings on their leaves called stoma. If your plants don’t get enough potassium, they can’t open those stoma efficiently and their entire respiratory system starts to kind of fall apart. Potassium is used in many other metabolic and growth-related functions, as well. If you don’t have enough, your plants are doomed.
Amending the Garden
There are lots of different things that might be going wrong in your garden, which you’ll know all about because of your soil test results. Since the combinations are nearly endless, we’ll discuss amendment in a sort of general sense. Otherwise, you’ll be reading all night instead of taking care of your garden!
If you’re using a general purpose fertilizer to correct your N-P-K (Nitrogen-Phosphorus-Potassium) issues, you’ll want to apply your fertilizer of choice to the bed you’re working long before planting. Typically, the bag will say how much to mix into the soil per square foot or per foot of growth if you’re fertilizing a tree or big shrub. All you need to do is scatter the granules across the soil and cover them with an inch or so of soil. Watering the whole thing will help prevent any sort of blow-away and allows the fertilizer to start moving deeper into the soil.
As for what to buy, if N, P and K are kind of the same on your soil test, go with a balanced fertilizer. A 10-10-10 or 20-20-20 will provide equal parts of each of the NPK components. If you have a lot of nitrogen, for example, and simply want to improve your potassium levels, then just buy a fertilizer that breaks down into potassium. It’s really that easy.
pH problems are harder. Much harder. You can get lots of different products to adjust that pH, some are organic, in that they’re made from plant materials, others are strictly chemical. The main advantage of the chemical treatment is that it can change the pH of the soil very quickly. Organic amendments, on the other hand, have to break down before they can start being effective. Those are really best applied in the fall so that they have all winter to turn into juicy plant nutrients. The fall is also a great time to apply compost to keep your soil light and airy.
No matter which products you choose, it’s important to give it a little time (at least a week) and sample again before making any other changes to the soil. Correcting soil problems is a slow process, but when you’ve mastered the garden, you’ll be able to plant exactly what you want there and find tremendous success.