The weather is starting to warm up, I have a pea trellis and I have planted peas, carrots, radishes, and turnips seeds as well as some kale seedlings I started indoors. We’ll see how they do in a few weeks.
For those who are just starting their garden, now might be a good time to consider a soil test.
Why get a soil test?
I got my first soil test last year when I first acquired a plot at Symphony Road Community Garden in Boston. My main motivation for getting a soil test was to check the lead levels of the soil. A lot of soil in the Boston area is contaminated with lead due to the use of lead paint on many residential homes until it was banned in 1978. I wanted to see how much lead was in the soil before I planted anything.
Other reasons for getting a soil test include the following:
- Helps you improve yields
- Helps you save money (don’t buy/apply nutrients the plants don’t need)
- Helps you manage the nutrients in your soil (know which nutrients to apply)
- Helps you optimize soil health (the importance of organic matter is discussed below)
Soil Test Results
The most important numbers on your soil test are pH and CEC (cation exchange capacity).
If the soil pH is not within the range that your plants need, they may not be able to absorb all of the nutrients that are available in the soil. Most plants need the soil pH to be between slightly acidic to neutral. The following chart provides the ideal pH ranges for some plants.
|Ideal pH range
||Blueberries, rhododendrons, and azaleas
||Green beans, cabbage, carrots, cucumbers, kale, lettuce, peas, onions, peppers, spinach, and squash
||Most garden plants and turfgrasses
Cation exchange capacity is a measure of the soil’s ability to hold moisture and nutrients. The lower the CEC, the more sandy the soil and the lower the capacity to hold nutrients. The higher the CEC, the more clay-like the soil, and the higher the capacity to hold nutrients. If you add organic matter to sandy soils, the CEC increases, if you add organic material to heavy clay soils, the CEC decreases (more on organic matter below).
What do soil test results looks like?
Click here to see what my soil test results looked like for my plot at Symphony Road Community Garden. Surprisingly, my garden plot has very low lead levels and contains a lot of nutrients! If you are unfortunate to have higher lead levels in your soil, all hope is not lost:
What if you have high levels of lead in soil?
- Locate gardens away from old painted structures and busy roads
- Plant fruiting crops
- Incorporate organic materials
- Lime soil to pH 6.5—7.0 (Lead is less soluble at this pH)
- Discard outer leaves of leafy crops and peel root crops
- Mulch soil surface to keep lead dust to a minimum
- Use a raised bed and fill it with other soil (This can be pricey).
Where can you get a soil test?
For those who live in Massachusetts, you can order a soil test from UMass Amherst. That’s where I got my soil tested, and it only cost me $15. See their website for order forms. My soil test results above are only for the Routine Soil Analysis, but if you get a soil test you should consider getting the Organic Matter Composition Test as well for an additional $6.
Organic matter is the remains of plant and animal life in the soil. The amount of organic matter will affect the soil’s structure and drainage. Ideal soil contains approximately 50% solid material (roughly 45-50% minerals and 2-5% organic matter) and 50% open or pore space (25% air and 25% water). Sandy soil will not hold water and nutrients well while clay soil can hole water and nutrients but can pack down, decreasing aeration and making it difficult to till. Clay soil also because hard when dry, which can restrict root growth.
Addition of organic matter will both clay and sandy soils. When added to sandy soils, organic matter will help bind sand particles together, increasing their capacity to hole water and nutrients. In clay soils, the addition of organic matter will increase granulation which will allow water to move through the soil more quickly. Compost, composted manure, leaf mold, and composted grass clippings are good sources of organic matter.
When to get the soil test?
For those who have just acquired a plot in a city that is known for having lead paint in the soil, such as Boston or Cambridge, you might want to consider testing the soil before you plant anything edible in it. However, now is peak season for ordering soil tests, and it can easily take over two weeks to receive your results. If you can wait, you can test your soil in the fall or even in the early spring as soon as you are able to get a shovel into the soil.
If you decide to get a soil test and you’re part of a community garden, it might be nice to share your soil test results with others, especially if the soil has high levels of lead.