10 Soil Indicators for Your Vegetable Garden

Ten soil indicators that could signal that your plants are in trouble.

Healthy Vegetable Garden

Maintaining healthy soil pays off in the end.

David Liebman

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The fun of gardening can quickly turn to frustration if a row of squash fails or your tomato plants produce no fruit. At some point, even the best gardeners must put on their detective hats and find out what went wrong.  While deer prints may be a dead giveaway, most gardening problems stem from less-obvious problems with soil health. Luckily, poor soil leaves clues that are easy to spot with practice. Gardening experts have compiled 10 warning signs of trouble in the garden. Knowing these, you can troubleshoot your own garden.

Do the numbers

Doing a soil test is as important to gardening as getting a survey done before you begin building a house. A good soil test will tell you the pH balance of your soil, as well as its levels of key nutrients. Troubleshooting soil health is easiest to do before anything is planted, says John Jemison, water quality and soil specialist at the University of Maine Cooperative Extension in Orono.

“Gardeners really need to do a soil test as a first step because then they have a plan,” he says. 

Not all soil tests are created equal, however. Susan Littlefield, horticulture editor with the National Gardening Association in South Burlington, Vermont, has found wide variables between soil tests. While there are affordable DIY soil tests on the market, Littlefield recommends getting your soil tested with a professional tester or through a cooperative extension office before taking action. For more, see “Know Your Soil” on Page 64.

Standing water

A garden should drain. If water pools in your garden long after a hard rain, that’s a problem. 

Nowhere is this problem more apparent than in the moist Pacific Northwest. Falaah Jones, an environmental educator with Seattle Tilth, gets many calls from gardeners with soggy crops through the organization’s helpline (206-633-0224). Eager gardeners plant too early in the wet spring in poorly drained ground, only to watch their seedlings die.

“People want to put in plants, and they jump the gun,” she says.

Roots need oxygen, and plants can drown just like humans. Ground that is too wet also can drain away valuable nitrogen, create mold and fungus problems, and block a plant’s absorption of necessary nutrients. Ground that is too spongy will need material to create air pockets to aerate the soil, such as hummus, as well as good draining material like sand.

Jones recommends taking a handful of soil and squeezing it. If water drips from your hand, look into finding ways to aerate the soil. 

Last year’s fruitcake

You can learn a lot about the health of your soil by sticking your hands in the dirt, says Eric Sideman, organic crop specialist for the Maine Organic Farmers & Gardeners Association in Unity. 

“It should have a crumblike structure, like the kind of coffee cake you used to buy,” Sideman says.

If your soil has a cracked appearance and feels as impenetrable as last year’s Christmas fruitcake, then you know you have a problem. It means that the soil has become an impermeable surface that won’t allow water to soak in, causing roots to have a difficult time growing down. 

A good first strategy is to add organic matter often. A second strategy is to avoid compacting the soil at all costs. 

Can’t take a punch

Even with flaky, dark soil in your garden, pests and plant ailments are still a fact of life, says Littlefield.

“You could have the best soil in the world, and you’re still going to have some insects and diseases,” Littlefield says. “The Japanese Beetles are going to come and eat your roses no matter what you do.”

Nothing will thwart a swarm of locusts, but if your garden gets hit hard by pests or disease, it may be a sign that your plants are stressed.

Plants have immune systems, just like humans, with built-in defenses like chemicals and thick skin to stop pests and diseases. But if the plant isn’t getting what it needs, it can become thin-skinned and unable to defend itself.

Littlefield cites the white birch tree as an example. In its natural forest habitat, the birch successfully fends off attacks from the Bronze Birch Borer, an insect that burrows into birches and lays eggs; the larvae eat their way into the tree. In a healthy birch, the larvae drown in the tree’s robust sap. But birches planted in the midst of a lawn are stressed and don’t produce the same flow of sap. The larvae survive and kill the tree.

If your garden often gets wiped out with whatever’s going around, it’s a good indication you need to work on your soil health.

Unexpected color

Unless you’re planting heirlooms, beware of unexpected colors on the leaves of your vegetables. 

If the lower leaves of a plant begin to yellow, it’s usually a sign that the plant has exhausted the available nitrogen. By letting the lower leaves die, the plant is prioritizing which leaves are most important for photosynthesis. You don’t want a plant to make that choice.

Sometimes, the nutrients are in the soil, but unavailable because of the soil’s temperature. If your plants look purple, they’re likely suffering from a deficiency of phosphorus. Oftentimes that doesn’t mean the phosphorous is absent in the soil, but that the ground might be too cold for the plant to process the stuff. Try using some mulch to warm things up.  

Funky roots

Sometimes, too much attention is placed on the color and health of the upper parts of plants and not enough on the root system. A plant’s root structure can tell an important story. 

Watch for clubroot, a common disease found in cabbages, radishes and turnips. The first sign of clubroot is wilting of the plant. Upon examining the roots, you will see swelling and a knobbly appearance, like the hands of a person with advanced arthritis. Once you see signs of clubroot, forget about planting any plant susceptible to the disease for a couple of presidential terms. Clubroot can hang around the soil for some seven years. 

Also, root issues can show a sign of pH trouble just as well as leaf problems. Visible scabs on potatoes might mean your soil pH is too acidic.

Amazon tomato plants

It would be easy to assume that the most common problem in the average garden is not enough nitrogen. But that’s not true, says Bruce Hoskins, assistant scientist with the University of Maine Cooperative Extension’s soil testing program. It’s just as easy to find a garden with too much nitrogen.

“You get a lot of horror stories,” he says.

People are becoming more aware about the need to feed their gardens at a time when commercial compost is becoming more potent, Hoskins says. Often, people overdo what they’re adding to the soil and end up throwing soil chemistry out of whack. While an influx of nitrogen might help plants grow lush, it sometimes can prevent them from giving you anything to eat. 

“If you have 4-foot tomatoes and delayed blossoming, that’s a sign of too much nitrogen,” says Hoskins, who recommends going slowly when adding compost or trace minerals into the soil. 

Not enough birds and bees

It isn’t always a glut of nitrogen that can lead to an absence of produce. Sometimes a plant blossoms but fails to cross-pollinate, Jones says. Enough critters and bees may not be doing the necessary pollinating work.

In the future, make sure to plant flowers in or near your vegetable garden to attract pollinators. In the meantime, you may have to do the pollinating yourself. No word yet from researchers if romantic music helps get plants in the mood.  

Unwanted company

Paying attention to what weeds pop up in your garden may help you discover soil problems, too, Littlefield says.

Moss more than likely means you have moist soil that is low in nutrients. Sheep sorrel means your soil is acidic and infertile. Guides are available to help gardeners determine what the weeds mean. Littlefield recommends Weeds: Friend or Foe? by Sally Roth, and Common-Sense Pest Patrol by William Olkowski.

Beware of volunteers

Many gardeners welcome volunteers that spring up without any work, be it a forgotten potato or a self-seeded tomato. But Jones recommends pulling those volunteers up as soon as they show their eager little leaves. 

Volunteers defeat crop rotation. When a plant grows in the same place year after year, it has a much greater chance of disease, she says. Volunteers have been hanging around all winter with last year’s rotting garden material and may act as carriers infecting healthy plants.

“There’s a host, and the organisms are already in there, and it completes the three-legged stool,” Jones says.

Garden problems almost always come down to soil problems. It can be frustrating to react to problems as they arise throughout the gardening season, but this year’s problems may help plan for next year’s solutions, gardening experts say. If you discover what your soil needs by troubleshooting, you’re positioning yourself for a gardening season with fewer problems.  

Craig Idlebrook has written for more than 30 publications, including MOTHER EARTH NEWS, Chicken Soup for the Soul and BackHome. He lives in New England with his 5-year-old daughter who likes to quote Shakespeare.