Linda Geist

COLUMBIA, Mo. – Sometimes, gardeners take the “if some is good, more must be better” approach, says University of Missouri Extension horticulturist Justin Keay.

But it’s possible to shower your garden with too much love in the form of fertilizer, manure and compost. More fertilizer and organic matter won’t necessarily produce more flowers or produce, Keay says. In fact, unnecessary fertilizers and amendments can be bad for the wallet, your plants and the environment.

“Adding nutrients you don’t need is a waste of money and can block the uptake of other nutrients,” he says. In addition, too much fertilizer or manure in a single application might result in excess salts that can stunt or kill plants. Excess nutrients can increase pollution in our lakes, streams and rivers, harming aquatic life.

A soil test can tell gardeners if they need to add fertilizers or organic matter. Garden soils that have been previously amended and fertilized over the years may have sufficient nutrients already. A soil test also will tell you the soil’s pH, a measure of soil acidity or alkalinity. A proper pH level is key to a thriving garden, Keay says.

Keay recommends testing every two to three years. Consider submitting separate samples for flower beds, vegetable gardens and lawns, where different amounts of fertilizers and amendments have been applied. Don’t forget to label samples and draw a map of your yard to show where the samples were taken.

Learn how to submit samples to the MU Soil and Plant Testing Laboratory at, or call 573-882-0623 for more information. Free soil test kits are available at county extension centers.

Keay and other MU Extension horticulturists discuss timely gardening issues during the “Weekly Garden Hour” held Wednesdays at noon via Zoom. Register for the free virtual event or ask a gardening question at Sessions are also livestreamed at

Sign up for the Garden Spade, a free monthly gardening e-newsletter, at

Resources from MU Integrated Pest Management:

• Video – “Understanding Your Soil Test,”

• Article – “Soil Testing for Healthy Lawns and Gardens,”

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