Get to know your soil: Testing for nutrition, pH, and soil safety

One thing I think we can all agree on is that spring in Vermont is like rolling the dice, and this year, we landed on snow. The ski industry has been happy as can be, but we gardeners…WE ARE READY TO DIG!!! And dig we shall!

Soils in Vermont (and Chittenden County in particular) quickly change from clay…to sand…to nutrient-rich…to contaminated in just a matter of acres, which is why it’s a good idea to get to know YOUR soil before the gardening season starts.

Being able to answer the following basic questions about your soil will help you become a more well-informed, confident gardener:

  1. What type of soil do I have? Is it sand, silt, clay, loam?
  2. How nutritious is it?
  3. What is its pH level?
  4. Is my soil safe? Are there contaminants?

Soil Type

Soil type refers to specific particle sizes within it. Particle size in soils correlates with how much water is retained or drained. Soil particles can be large (like gravel) or small (like clay) and anywhere in between.

The best soils have many different particle sizes throughout, and you’ll quickly find that particle size uniformity can lead to problems with water retention and/or air circulation. Once you figure out what type of soil you have, you’ll be able to decide how best to amend it.

For example, for sandy or clay soils, a general rule of thumb is to add mature compost, which is full of organic matter that will greatly improve soil quality.

How to figure out soil type

Touch it

Just pick up a bit of soil and rub it with your fingers. A gritty feeling indicates sand, which most of us are familiar with from playing in sandboxes as kids.

A sticky feeling is clay—particles that are so small they stick together. Imagine crushing up a peanut. When the peanut is first crushed, it feels gritty because the particles are large. Keep grinding and you’ll get tiny particles–sticky peanut butter!

Do a water separation test

Fill a mason jar with an inch or two of soil and add a spoon of salt. Fill the jar with water and shake. After a couple of days, you will see the different soil types separate. Clay will be on top, followed by silt, followed by sand on the bottom.

Nutrients, pH, and Contamination

Nutrients are an important factor when getting to know your soil, as they become the building blocks of plant health. Nitrogen (N), Phosphorous (P), and Potassium (K) are known as primary nutrients and are responsible for healthy foliage (N), strong root systems (P), and overall plant health (K).

In the same way that many of us refer to the “Nutrition Facts Label” on our food packaging to decipher our nutrient intake, a soil test can provide us with the same kind of helpful information about our soil. Once you know nutrient levels, you can amend your soil accordingly using commercial fertilizers, compost, or manures. But be careful to know what you’re adding, because too much of one thing can cause problems in other areas.

Soil pH is another important factor in getting to know your soil. pH measures the acidity or alkalinity of soil and is measured on a scale from 1 (acidic) to 14 (alkaline).

A pH of 7 is considered a neutral soil. This is the level we want to shoot for—where nutrients are most easily accessible by plants.

Soils with a pH below 5 or above 8 may be harmful to plants. Some plants, however—like blueberries, for example—do well in soils which have a low pH.  If you have acidic soils (i.e. a low pH), adding mature compost is a great way to help level out the pH.

Contamination becomes a factor mainly when gardening in urban settings. In Vermont, lead is a very common metal found in urban soils and is one of the most dangerous as it can be absorbed by the roots of vegetables and then eaten. Other heavy metals to look out for are nickel, cadmium, and chromium. If you have any suspicions that your soil is contaminated, get it tested or start thinking about container gardening!

How to figure it all out

Simple soil testing kits are available from many university extension offices and at some garden centers. The University of Vermont offers an inexpensive ($14) basic nutrient test that includes results for basic nutrient content, pH, and organic matter, as well as fertilizer recommendations for one crop ($2 for each additional crop you’d like recommendations for).

You can add on a heavy metals test ($10) if you think your soil could be contaminated.

For more, visit the University of Vermont soil testing page for a list of their tests with the results provided for each. Then, dowload the forms on their site here (it’s not entirely obvious how to get to the forms).

Two average samples

Then, follow along as we do a few soil tests of our own at our facility here in Williston! We took samples from an established raised bed as well as a grassy, previously unplanted area. We will be posting the results as they come in, and writing more about how to interpret them and amend the soil for the best possible results.

Once you’ve gotten to know your soil, it’s important to keep up with that relationship. Each year that you are growing food, basic amendments and nutrients will need to be replenished in order to make your garden a success. And remember: Regardless of how well you know your soil, adding a quality compost to your lawn or garden is always a safe bet.


Resources

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