6 Major Signs Your Plants Are Begging You to Test Their Soil, Gardeners Say

When is it time to perform a soil test? Believe it or not, your plants will let you know. If your garden plants start experiencing slow growth, weak stems, or yellowing leaves—all of which are common indicators of nutrient deficiency or improper pH balance—it may be time to test your soil’s vitamin levels.

Here, we chatted with garden experts to find out what other signs you should be looking for and what can be done to fix them.

Yellowing Leaves

When your plant’s lower leaves begin to turn yellow, it often means the plant isn’t getting enough nutrients from the soil.

“Nitrogen deficiency is a common culprit, but it could also be related to pH imbalance, which prevents nutrient uptake,” Annette Thurmon, a gardener, homesteader, healthy living advocate, and author at Azure Farm, says.

But since yellowing leaves may indicate anything from a lack of nitrogen or magnesium, or even iron deficiency, it’s best to determine what exactly is missing from your soil by administering a soil test. Usually, overly alkaline soil is the problem, Thurmon says, and you will need to raise or lower your soil’s pH.

Still, she recommends reading the soil test results carefully. So, pay attention to the pH level and the key nutrients like nitrogen, phosphorus, and potassium. Also, look at micronutrient levels like calcium, magnesium, and sulfur, she says.

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Wilting Leaves, Even When Watered

There are a few possibilities for what’s ailing your plants if your plants look droopy or wilted, even though you’ve been watering regularly. While all these symptoms could indicate poor drainage or compacted soil, Thurman says, it could also be a sign of root stress caused by pH issues or nutrient lockout. Poor drainage and compacted soil are easy fixes: just break up the soil to help water reach the roots.

But to determine an improper pH that can disrupt nutrient absorption, you should test your soil. After seeing the results, balance the pH levels in your soil.

“If the soil is too acidic, you can add lime,” Thurman recommends. “If it’s too alkaline or sulfur, composted organic matter can help bring it back into a healthy range.”

Purplish Grass Leaves

Poor soil quality doesn’t just affect your garden plants. It can wreak havoc on your lawn, too.

“Purple leaves are a classic sign of phosphorus deficiency, and the most common deficiency we see,” Maggie Reiter, lead scientist at Sunday, says.

Therefore, you will want to check any soil tests for phosphorus levels. To fix the problem, fertilize with a phosphorus-containing fertilizer. But excess phosphorus can harm water quality, so only apply phosphorus if your soil test shows a deficiency, Reiter warns.

Green Leaves, but Poor Flowering or Fruiting

This is another cry for help from your plants.

“If the leaves are green, and the plant seems to be growing ok but experiences poor flowering or fruiting, that can be a sign of a phosphorus or potassium deficiency,” Kevin Lenhart, landscape designer and gardener at Yardzen, says.

However, too much nitrogen can cause lush green leaves but no flowers, too, Thurman adds. For this reason, it’s always important to use a soil test to find out what the exact nutrient deficiency is. Then you can use the right soil amendment to fix the problem.

Stunted Plant Growth

When plants stop growing or seem small compared to others of the same kind, they may not be getting enough essential nutrients. If a vital nutrient like phosphorus is missing, a soil test will reveal this.

Then you will know what soil amendments to use that can correct it, like fertilizer that has the nutrients.

“For example, compost and aged manure can help with general nutrient deficiencies, while specific amendments like bone meal, kelp, or lime can target individual needs,” Thurman explains. 

Puddles or Standing Water

Pooling water indicates soil is compacted. But at the same time, it can mean the soil has a high amount of clay that holds in water, Reiter says. It’s important to run a soil test to detect exactly how much clay is in your soil.

For soil compaction, you can inspect the soil yourself to determine if it’s hard. Reiter suggests pushing a trowel or other garden tool into the turf to estimate its hardness. Then you can aerate the lawn to alleviate soil compaction. However, to reduce the amount of clay in your soil, you will have to add other soil amendments to produce more loamy soil.

“I would encourage gardeners to seek out organic materials that help build a nutrient-rich, well-balanced, and structured soil,” Lenhart says.