Here’s the hidden reason your plants fail, and a way to protect them this season
The planting season is finally upon us. Hopefully, you saved up some cash to go to your local retailers for new plant material. I know my bank account will take a hit this time of the year, and that’s true of the accounts of many other garden lovers in the Kansas City metro area. It hurts that much more when a plant doesn’t thrive as you’d hoped. Sometimes, you are left pulling out a plant tag next to dead plants, leaving you puzzled as to what went wrong. This article will reveal a little-known secret on how you protect your investment from physics.
When I was taking my introductory horticulture courses at K-State, I was in a class called landscape maintenance operations. Instructor Cathie Lavis taught us about an interesting phenomenon called the “soil interface effect.” It sounds complex and complicated to understand, and it is. But she wasn’t teaching it to us just for another high-minded college concept: The soil interface effect can explain why many of our potted crops fail when we put them into the ground.
The soil interface effect is soil particles’ interactions with each other and the greater environment. This relationship affects our plants by influencing things like water movement and nutrient uptake. Nutrients and water move through the soil due to differences in potential energy. High potential moves to low potential. In soil, this can look like water moving from sand to clay. Sand has a high water potential, meaning it doesn’t want to hold the water very tightly and will easily let it go, while clay has a low water potential, meaning that it will hold on to water tightly and won’t easily let it go.
When growers are growing plants in pots, they use a soil-free media that mainly consists of a blend of peat moss, sphagnum moss, pine bark, perlite and vermiculite, which all drain water quickly and don’t hold onto water as tightly as clay particles. Or, using the terminology from earlier, potting media has a higher water potential than clay particles. Water will flow from the potting media into the surrounding clay soil. The clay soil acts like a sponge, drawing the water away from the soilless media. This is the soil interface effect at work.
How many times have you checked your recently planted pots and noticed the plants themselves were dry, but the surrounding added soil or ground around the new plant was wet? Your shiny new plant is wilting and fading away.
Water being pulled out of the soilless media will lead to the majority of the established roots drying out. This can also be compounded when the soilless potting mix dries out completely. This is because it becomes hydrophobic, making adding water to the potting mix difficult. This is the cause of death to many large tree-planting projects and the perennials that home gardeners work with. Keeping your plants consistently watered in the first couple weeks after planting will help protect your investment.
Knowing this, you can plant new perennials, trees, or shrubs with confidence that you are giving them the best chance for survival. Trees with a root ball in soilless media need to be well watered before being placed in the ground, and the surrounding soil should also get a good soak. Otherwise, the water will be pulled out of the root ball and held tightly by the surrounding clay.
Anthony Reardon is a horticulture agent with Kansas State University Research and Extension. Need help? Contact the Johnson County Extension gardening hotline at 913-715-7050 or email garden.help@jocogov.org.
This story was originally published April 11, 2025 at 6:00 AM.