Gardeners eager to get outside and work in this year’s early warm weather should take care: It’s all too easy to damage your soil in early spring.
“The danger is that you’ll compact the soil if you dig it or even walk on it when it’s too wet,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. Compacted soil is so dense that air, water and plant roots can hardly penetrate it. “For plants, compacted soil is like concrete,” Yiesla said.
Clay soil, which is common in the Chicago area, is especially subject to compaction. Heavy and sticky, it is made of small particles that can easily be jammed tightly together. “Once those particles are packed, it’s extremely hard to unpack them,” she said. “Preventing soil compaction is much easier than trying to fix it.”
Healthy soil has space between its particles that allow air and water to flow through to reach a plant’s roots. Those gaps also allow tiny new roots to find their way through the particles and grow. Compacted soil is a barrier that stops roots from growing. Roots are a plant’s way of collecting water and nutrients; if it can’t extend its root system, it may not be able to collect enough water. Rainwater that falls on compacted soil often doesn’t soak down to where plants’ roots can get at it. That can give rise to a paradox: Wet, compacted soil in which plants are dying of thirst.
“When trees and other plants fail to thrive, it’s often because they are struggling in compacted soil,” Yiesla said.
Here are some ways to prevent soil compaction:
Avoid walking on wet soil. Delay your garden cleanup or lawn seeding for a few weeks, until the top few inches of your soil are fairly dry. “Soil particles pack together very easily when they’re wet,” she said. “Your body weight is enough to do some damage.”
Check the soil moisture. Before you begin work anywhere in the yard, dig up a handful of soil. It should feel moist, but not wet or muddy, and should just barely hold together when you squeeze it in your fist. “If you leave make a muddy footprint in the soil, it’s too wet to be in the garden,” said Spencer Campbell, Plant Clinic manager. “Wait for drier conditions.”
Spread your weight. If you must work on garden soil — to weed, for instance — use stepping stones, or step or kneel on something wide and flat that will distribute your weight. “Foam kneeling pads make good temporary stepping stones,” Yiesla said.
Watch your step. At any time of year, never dig or walk in any area that feels wet or soft underfoot, or where you can see standing water. “A small child splashing in a mud puddle doesn’t do much harm, but a full-grown gardener should steer clear,” she said.
Don’t dig too soon. Spring rains often leave soil wet, and digging in it tends to compact it. That’s true even if you’re digging in compost or other organic matter. “Wait to add amendments until things dry out a bit,” Yeisla said. “And wait to plant trees, shrubs and perennials until you can plant them in well-drained soil.”
Don’t dig at all if you don’t have to. Tilling soil or turning it over destroys the soil structure and brings weed seeds to the surface, and it usually isn’t necessary, even in vegetable beds. In most cases, except when starting a new garden, it’s best to simply top-dress with compost, spreading an even layer over the soil surface. Insects, worms, and microorganisms will digest the compost and pull it down into the soil. They will lighten and aerate the soil as they work.
“As a general rule, the less you disturb your soil, the healthier it will be,” Yiesla said.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.