Rules of thumb are useful guidelines for making things work most of the time. They are useful even for perfectionist gardeners like me. Most of the following rules of thumb come from my 25 years gardening in the Lowcountry.
Transplant before Memorial Day or after Labor Day. Plants, especially woody plants, transplanted from a nursery pot into the ground will struggle to establish themselves in the heat of the summer. It’s easier on the plant — and the gardener — to transplant in fall, winter and spring.
Herbaceous annuals and perennials can be set out in summer if careful attention is paid to watering. Outdoor plants can be planted in containers or repotted successfully during the summer.
Smaller is easier. It is easier to plant a 4-inch perennial than a 1-gallon perennial, just as it is easier to plant a 1-gallon shrub than a 3-gallon shrub. Small plants adjust more readily to transplanting than large plants. This goes double for trees.
Seeds are difficult. Outdoors, Lowcountry soils are full of damping-off pathogens, in other words, pathogens that kill new seedlings. Indoors, dim lighting and warm rooms produce weak, spindly seedings. For most home gardeners, buying vegetable transplants and annuals is the best option.
Seeds are fine for leafy vegetables, root vegetables, squashes, peas and beans if they are planted in raised beds or soil-free potting mixes.
Add compost every time a plant is planted. Compost should account for one-quarter of the soil in which the plant will grow. I was reminded of this rule of thumb when I set out "Profusion Yellow" zinnias for the summer. I used at least twice as much compost in each planting hole as I normally do, closer to the 25 percent rule. The zinnias “took” quickly and have grown and bloomed steadily all summer.
Start a compost pile when the lawn still needs mowing. Nothing gets a compost pile working quickly like fresh grass clippings. Mix grass clippings and early fallen leaves in a 1:2 ratio and water well.
Control weeds when they are small to prevent them from setting seed (annuals) or spreading (perennials). I have eliminated several annual winter weeds, including chickweed, wild geranium, henbit and bitter cress, from my yard by following this rule of thumb. Unfortunately, it doesn’t work as well with summer weeds.
Water grass and other plants when they are dry. This seems so obvious, but unfortunately it is common during a dry spell to see lawns dry up before homeowners water them.
Centipede doesn’t grow like Kentucky bluegrass, the common lawn grass in the Midwest, which goes dormant in the summer when it’s dry. When centipede lacks water, it slowly dies back and thins, leaving room for weeds to grow.
The most important rule of thumb has been stated many times by many successful gardeners: right plant, right place. It is foolish — and expensive — to put a perennial plant, especially a large shrub or tree, where it will be unhappy, that is, a place too wet or too dry, too shady or too sunny.
For woody plants, “right place” includes a spot large enough for the mature plant to grow. All perennial plants are sold with tags listing their expected size. Gardeners who prefer tight plant spacing can use the smaller dimensions as their guide, while gardeners who prefer a more open arrangement should use the larger dimensions.
For optimal air circulation around houses, especially ones with wood siding, leave 3 feet of space between the mature size of a foundation shrub and the house. To calculate, add 3 feet to one-half of the mature width of the plant, and then measure this distance from the wall to find where to dig the hole.
Grow a variety of plants. With the variable climate in Charleston, no plant is perfectly happy all the time. Growing a variety of plants provides natural diversity, which prevents one pest from having a major impact on the yard, and fits a modern gardening style.
One more rule of thumb comes from Eric Shealy at Riverbanks Zoo and Garden: “I always include at least one native (plant) in every bed I design.”