Planting a plant is like building the foundation of a house. Everything that comes afterwards depends on the foundation, whether it’s the livable portion of the house or years of good growth. Extra time and care spent planting will be rewarded with improved plant growth.
Preparing the soil
Most South Carolina soils should be amended before planting. Adding organic matter to soil increases the amount of water that sandy soils hold and the amount of air space in clay soil. Adding topsoil also can improve plant growth by shifting soil closer to the ideal mix of equal parts sand, silt and clay.
Organic matter added to soil should be well composted without pieces of bark or wood. As woody bits finish decaying, they pull nitrogen out of the soil and away from plants.
An easy way to measure how much organic matter to add is to layer two inches over the planting area and spade that into the ground to a depth of six to eight inches to end up with a mixture of one part (two inches) compost and three to four parts soil.
If the entire raised bed will be planted at the same time, fertilizer can be spread and mixed in with the compost.
Stimulating root growth
Good root growth leads to good plant growth. Planting is the main time when gardeners can aid root growth.
Roots, like shoots, need water and air to grow. Fresh, homemade compost, the ideal source of organic matter, holds billions of microorganisms, including bacteria that improve root growth.
If the plant has been in the pot for a while, the bottom of the pot likely is filled with a dense mat of roots. Some gardening gurus advise against planting rootbound plants at all. Sometimes, there are no alternatives.
To stimulate new root growth on a rootbound plant, slice off the bottom one-eighth inch of the root ball. The bottom edges of the root ball should be loosened. It may be necessary to make several one-inch cuts into a very dense root ball to do this.
The planting hole
If a plant is set into a raised bed of amended soil, the planting hole need only be a bit wider than the pot, just enough to easily set the root ball into the soil.
If the plant is being planted as a single specimen directly into native, unamended soil, then the planting hole should be two or three times as wide as the pot. The soil that is used to fill the hole should be amended as described above.
Not so deep
One of the main causes of poor plant growth, for trees and annuals alike, is planting too deeply. Potting soil is light and porous in pots, but once a plant is set in the ground, the potting soil compresses, which pulls the plant lower into the ground. Likewise, freshly amended soil has extra air in it, and as rain beats down on the bed, the soil also will compress over time. Setting a plant slightly above the top of the soil compensates for this settling.
Exactly how far above the top of the soil depends on the size the plant, the type of potting mix and the soil. Small plants in three-inch-diameter pots should be set one-quarter to one-half inch above the soil line in the raised bed. A 2.5-quart-sized perennial should be set at least one-half inch above the soil line. A three-gallon shrub should be set one inch above the soil line.
Another likely, but easily avoided, cause of plants sitting too deep in soil is digging the planting hole too deep. I made this mistake in my early days of gardening, when I thought that the soil underneath the plant also should be amended. Planting instructions on most nursery tags now agree that the hole should be dug the same depth as the height of the root ball.
Before digging a hole for woody plants, it’s a good idea to pull the plant out of the pot to check the height of the root ball. Sometimes the root ball will not fill the entire pot if the plant was put into a larger pot right before shipment to a garden center. (I have unknowingly purchased several plants like this.) In this case, the planting depth should be based on the root ball, not the pot.
Once the plant is centered in the hole, it’s a good idea to step back and check the placement before filling the hole. The plant should be level vertically and horizontally.
If fertilizer was not mixed into the raised bed, slow-release fertilizer can be mixed with the soil used to fill the hole, or it can be added in the middle of the hole.
After half of the planting hole is filled with soil, the soil should be watered lightly to settle it. This step also will minimize undue settling of the soil and the plant later.
The planting hole should be filled with soil up to the top edge of the root ball. To prevent planting too deeply, don’t cover the root ball with soil. Instead, water thoroughly and cover the bed with your favorite mulch. Right around the plant stem, the layer of mulch should be thin, no more than an inch deep, to prevent trapping excess moisture after rain or watering. Trees are particularly fussy about mulch not touching their bark.
Time spent amending soil with compost, digging the right-sized planting hole, and carefully positioning the plant will help plants grow vigorously.