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Garden Advice

Getting a Soil Test

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Soil tests are a simple and accurate way to learn more about your garden soil and determine what amendments it needs. A detailed soil test, a little research, and an understanding of the results can drastically improve your yields and eliminate recurring issues in your garden.

Where to Get Soil Tested?

There are a few ways you can get a soil test. While you may find simple home test kits at your local hardware store, these generally aren’t as accurate or detailed as a professional test. 

Typically, you can get your soil tested through your county extension agency or agricultural college. Many extension agencies and state colleges offer residents free or cheap soil testing. They typically include some recommendations if amendments are needed. Private labs also provide these services, but they may not be as affordable for home gardeners as the other options.

How to Find Your County Extension

To find your county extension agency try browsing the listings of Pick Your Own. They list contact information for county extension agencies across the United States.

When to Sample

We recommend having your garden soil tested every one to two years. Orchard areas typically only need to be tested every three years.

Late summer and fall are ideal times to collect soil samples. This time of year will represent how the soil’s nutrient status affects crops. If needed, you can take soil samples in spring, but you should avoid collecting frozen or waterlogged samples as they may not mix well.

Don’t collect soil after adding lime or other amendments. It’s best to wait several months or even longer if the weather is dry until they’ve dispersed into the soil.

Depending on the lab you’re working with, and how busy they are, it may take several weeks to get the results from your sample. It’s best to send them in well before you need the results.

Where to Sample

You want to get a good picture of the soil throughout your garden, not just in one spot. To do this, you’ll create a composite sample to send in, made from samples taken throughout the garden. For small-scale home gardens, five to eight samples are generally adequate. 

If your garden appears to have distinct slopes and soil types, be sure to get a sample from each area. Avoid taking samples from sites that don’t represent your garden well. These may include garden edges and unique wet spots.

How to Take a Soil Sample

Take soil samples using a spade or auger and collect them in a clean container. How deep you should sample depends on your garden type. Aim for small uniform cores or thin slices starting at the soil surface. 

For traditional backyard gardens, sample to the tillage depth. For no-till gardens, take one sample from the top 1 inch of soil and then take a second sample from the same spot at a depth of one to six inches.

For areas you’d like to establish an orchard, take a surface sample from zero to six inches deep and a subsoil sample from six to twelve inches deep. In established orchards, scrape aside plants and organic matter and take a surface sample. 

Once you’ve collected your samples, gently crush them and remove any stones and roots. Then allow your soil sample to air dry. Spread it out on a clean surface in a shady spot and make sure it dries before mailing. Don’t heat your soil to dry it.

Your samples should be at least one cup of soil in a plastic bag. Depending on the agency or lab, they may have you use or provide a specific bag. Follow your extension agency or lab’s instructions for sending your sample. Be sure to include all necessary paperwork and your name and address. 

 

The gardening science can sometimes feel intimidating, but it doesn’t have to! Getting your soil tested is a simple way to learn how to amend and improve your soil correctly. Your soil test and advice from the local extension agency can help you build healthy soil and grow healthier, more productive plants.



Garden Advice

Common Nutrient Deficiencies in Plants

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Spotting nutrient deficiencies in your plants can be challenging, especially if you’re new to gardening. Here are what a few common deficiencies look like and how to correct them.

Soil Nutrients

Nutrients in the soil can be divided into two categories macronutrients and micronutrients/trace minerals.

The first category, macronutrients, comprises primary nutrients nitrogen, phosphorus, and potassium and secondary nutrients sulfur, magnesium, and calcium. If you think your plant has a nutrient deficiency, these are the likely culprits.

The second category, known as micronutrients or trace minerals, includes boron, chlorine, copper, iron, manganese, molybdenum, and zinc. While these are still important to plant health, they’re needed in such small quantities that it’s less likely your plant is deficient in one of these micronutrients.

You can read more detailed descriptions of what all of these nutrients do in our post, Understanding Soil Tests.

Nitrogen Deficiency

A nitrogen-deficient plant will grow slowly and lack vigor. The leaves may turn pale and yellow before dropping off, with the oldest leaves dropping first.

Note that it’s easy to overdo it when adding nitrogen, especially if you’re using chemical fertilizer. Adding too much nitrogen will cause lush, dark green foliar growth at the expense of fruit and flower production.

There are many ways to add nitrogen to your soil. While you shouldn’t directly apply it to plants, animal manure is a good choice if you have access to it. Compost will also add some nitrogen, or you can add seaweed or kelp meal, fish emulsion, bone meal, coffee grounds, soybean meal, or cottonseed meal. Using legume cover crops also helps to increase your soil’s nitrogen levels.

Phosphorus Deficiency

A plant that is deficient in phosphorus will also lack vigor and may be stunted. It might drop fruit before it’s ripe or not produce fruit at all. The lower leaves may appear red or purple.

You can add phosphorus to your soil using rock phosphate, greensand, compost, or bonemeal.

Potassium Deficiency

Potassium deficiency will probably be most apparent in your plant’s leaves, which may be mottled or curled or have brown edges. The plants will also be weak and have stunted root growth. They will likely be more susceptible to disease and pest issues.

Good potassium sources include manure, compost, seaweed or kelp meal, potash, granite dust, greensand, and wood ashes.

Sulfur Deficiency

While sulfur is a macronutrient, a sulfur deficiency is much less common. Signs include stunted growth and pale, yellow leaves.

Add sulfur with gypsum, compost, or sulfur.

Magnesium Deficiency

If your plant is deficient in magnesium, you may notice poor flower and fruit production, stunted growth, and dropping leaves. Leaves may also appear mottled with yellow/white patches or purple/brown patches between the leaf veins.

To correct a magnesium deficiency, add limestone, manure, compost, or greensand.

Calcium Deficiency

Calcium deficient plants may die back or have buds that die. Their leaves will likely appear burnt, curling, or have necrotic leaf margins. You may also notice issues like blossom end rot and other signs of tissue necrosis.

Use oyster shells, eggshells, limestone, gypsum, or fishmeal to add calcium to your soil.

Notice how similar a lot of these symptoms are?

If you’re having problems with nutrient deficiencies, the best advice is always to get your soil tested. It isn’t complicated or expensive and will tell you precisely what you need.

It will also tell you what your soil’s pH is. Soil pH can affect plants’ nutrient uptake and may cause deficiencies even if your soil is otherwise fine.

If your soil test comes out fine, your plants may be struggling due to over or underwatering or disease issues.

How do I prevent deficiencies?

The first step you should take is to develop a garden rotation plan that includes cover crops. They’re excellent for preventing erosion and adding nutrients to your soil.

Yearly applications of good quality compost can provide a wide range of nutrients to your soil.