When Is the Best Time of Year for a Soil Test?

There are many ways to visually assess your soil’s health, like checking its structure and texture and noting its density of earthworms and other soil organisms. But there are important soil components that you can’t see, which are equally vital for a successful garden and lawn. That’s where soil testing comes in.

“Don’t guess, soil test,” says Steve Reiners, professor at the School of Integrative Plant Science Horticulture Section Cornell AgriTech and advisor for Tertill. “Many people waste money and time applying unnecessary fertilizers. Not only does this waste resources and harm surface and groundwater, but it can adversely impact plants. In the garden, you can have too much of a good thing, for example nitrogen,” Reiners warns.

As far as when to do a soil test, below are some pointers. However, more important than when is how to collect samples for an accurate test, as that’s the bit gardeners and homeowners often get wrong.

What Is a Soil Test?

Soil test results tell you if your garden or lawn is deficient in any of the nutrients or conditions plants need to thrive. A standard test might include soil pH, salt content, available nitrogen, phosphorus, potassium, calcium, magnesium, sodium, sulfur, copper, iron, manganese, boron, zinc and heavy metals. Soil test kits can be purchased from a lab, extension office, university or online retailer, and vary in price depending on how many elements are included in the test. Search “soil testing near me” to find options in your area.

Note: The consensus is that at-home soil tests that are not sent to a lab for analysis are less likely to give accurate results (our expert made the analogy to at-home Covid tests).

What Is the Purpose of a Lawn or Garden Soil Test?

Homeowners have their lawn and garden soil tested to find out if there are deficiencies. Once you know what you need to amend in your soil, for example altering your pH or adding organic matter, you can target those areas to make your plants more healthy. Soil test results usually include recommendations for which nutrients, and how much of each, to add to the soil for optimal plant growth.

What Is the Best Time of Year for a Soil Test?

Fall or spring, to give whatever soil amendments you find out your soil needs time to do their thing. Many people wait until spring, but testing labs are usually more busy then, and consequently wait times are longer. You don’t want to wait too long, or you could risk running out of time to get soil amendments in place before planting. Also, if you live in an area with a really damp spring, fall may also be a better time, because collecting a quality sample from soggy ground is more difficult.

However, seasonal timing is not as important as collecting an accurate soil sample, says Barbara Shea, master gardener at Tertill. “If your soil has never been tested before, there is no best time,” she says. “Just do it so you can have an idea of your soil’s health.”

After the initial test, it’s good to retest every two to three years.

How Do You Take an Accurate Soil Sample?

To collect soil samples, dig small holes about six to eight inches deep in the parts of the garden and yard you want to test. Fill a bag containing one or two cups of soil from each area: garden, vegetable garden, lawn. It’s important to not mix soils from different parts of the yard as each can have different results.

“Labs have different protocols, so there isn’t one size fits all ” says Reiners. “For example, some labs will accept damp samples, others will not.” Because of this, it’s important to closely follow the directions provided with the test kit. Here are some other protocols to keep in mind:

1. Test one area at a time. If you are testing your lawn, don’t include soil from your garden and vice versa.
2. Use a clean trowel and pail to collect each area.
3. Avoid including samples from unusual spots like under eaves, near brush piles or next to compost piles.
4. Remove grass, mulch or debris before sending in the sample.
5. If the soil needs to be dry, spread it on paper and let it air dry. “Do not dry the soil in an oven or microwave because this changes the potassium chemistry in the soil,” says Reiners.
6. Repeat these steps for each planting area (lawn, garden, orchard) you want to test.
7. Multiple samples can usually be submitted for testing, such as your lawn and your garden. Be sure to accurately label and identify each bag.

The lab will do a chemical analysis and provide you with the results.