How to test your soil for a healthy garden

soil test kit:

Commercial soil testing kits can help you locate the cause of many garden problems.

It’s spring — and we urban gardeners are itching to throw some seedlings into the ground. But wait! Before we proceed, let’s review how we did last year.

Did any of your veggies poop out early in the season? Or never thrive in the first place? It’s likely because of the condition of the soil.

This season, rather than planting first and dousing with a fast-acting fertilizer (as some of us have been known to do… ahem…), let’s do it right. Shall we?

Farmers, nursery experts and master gardeners know that Step No. 1 in the health of any garden is the soil. University extension programs and commercial services are available to test your soil. But there are also a number of kits available from your local nursery or garden store that can give you a good idea of the conditon of your soil.

Soil test kits

After consulting a garden expert at the newly opened Green Acres nursery in Elk Grove, I selected a Rapitest soil test kit by Luster Leaf. (No, they’re not paying me to review this test, although it is available in the Little Green Wheelbarrow store.)

This type of kit — versus a probe-type soil analyzer — is recommended because it tests not only pH but nitrogen, potash and phosphate levels as well.

A Rapitest soil test kit from Luster Leaf.

A Rapitest soil test kit from Luster Leaf.

As you can see from the photo, my garden plot needs help. It’s a reclaimed landscape bed that for decades sat beneath rock, with little or no organic material making its way into the soil. Not only that, but recent renovations to an old paved walkway left wheelbarrows full of sand and gravel piled on top. It’s time for some tender loving care before it’s ready for vegetables.

Sample the soil

The first step is to gather samples of the soil. Not all areas of your garden are created equal, as some may have more or less of what your soil needs to be healthy. In my case, some areas are newly reclaimed, while other areas were used as a compost pile last year. I chose three areas to test.

Sample several areas of the garden.

Sample several areas of the garden.

The instructions with the test kit recommended taking a sample about 4 inches deep. Remove stones and large sticks, and mix the soil thoroughly. You’ll need less than a thimbleful to test.

Do not touch the soil with your hands, or it may throw off your results. Place each sample into a separate clean receptacle.

Remove a small sample of soil to test.

Remove a small sample of soil to test.

I could see that two of my samples contained quite a bit of sand, while the one in the area of last year’s tomato plants contained more organic material.

Three soil samples ready to test.

Three soil samples ready to test.

Mix up the tests

Begin the pH test by adding soil, the powder capsule and water (distilled if possible) to the kit.

Shake the capped kit and after a minute or so compare the color of the water with the pH chart. This sample appears to have a pH of about 7.0, or slightly lower. With some good organic fertilizer added to the mix, this garden’s pH looks healthy enough.

Compare the color of the water with the chart on the test kit to determine pH.

Compare the color of the water with the chart on the test kit to determine pH.

Generally speaking, most plants will do well in a neutral pH environment. There are some plants that prefer a more acidic environment, but certainly most can tolerate a range of pH levels within one or even two points. Check with your master gardeners or the guide that comes with the test kit.

N, P and K levels

As my Rapitest kit also tests nitrogen, phosophate and potash levels, I continued on per the instructions. For this test, I combined all three samples and mixed with 5 cups of water. To encourage the sediment to settle, I put the liquid in an old water bottle and removed the test liquid with the eyedropper after about two hours. Clay soils will take longer to settle, and sandy soils less time.

Besides pH, test nitrogen, phosphate and potash levels to improve soil health.

Besides pH, test nitrogen, potash and phosphate levels to improve soil health.

The test (purple lid) reveals my soil to be pretty deficient in nitrogen, which is probably due to the large amount of sand added from the old walkway base. The potash test (orange) shows the soil to be similarly depleted. Phosphorus, in blue, is adequate but certainly could be improved.

The instructions in the test kit recommend using dried blood or nitrate of soda to amend the nitrogen, bone meal or triple superphosphate to amend the phosphate, and muriate of potash to amend the potash levels. Other fertilizers are available, depending on your preference, so check the package for the percentage of nutrients for nitrogen, phosphate or potash and adjust the amount accordingly.

As for me, I’ll head back to the nursery, test results in hand, and ask their advice.

I hear they’ve got a great soil conditioner with worm castings and bat guano. Yum, yum.


Kristi Garrett

Kristi Garrett is the Publisher, Editor and Chief Veggie Enthusiast of Little Green Wheelbarrow. After 16 years in journalism and corporate communications, she figures it's time to get some dirt under her nails.

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