by Janet Woody, Librarian, Lewis Ginter Botanical Garden
Recently we had a request for information about growing vegetables and flowers in a raised planter. Since I am not sure if this question pertains to a planting box with sides that sits right on the ground, or a raised planter box with its own, possibly slatted, bottom to keep the soil from falling out. I’ll try to answer both ways.
If you are new to gardening, starting with raised planter box is a good choice. Digging in the ground can be hard and discouraging. Plus you can move your boxes around and if you get tired of the plants in it, pull them out easily and start again. If you use annuals, you will have to replace them periodically. You can mix perennials and annuals if you like. Annuals usually last one season and perennials can last indefinitely, but these things aren’t written in stone. Herbs are often perennials and are fun to grow in containers indoors and out.
First of all, does the container have holes in the bottom for drainage? This is essential. Don’t plant anything (unless it’s an aquatic plant) in a container without a hole.
If your planter box sits on the ground, and you will be using the soil that is already there, as you dig holes for your plants you may want to add organic matter such as leaf compost, or purchased, bagged compost. Sand is not necessary unless there is a drainage problem. Builder’s sand works well, just don’t overdo it.
For your raised container (off the ground), use a good potting soil made for container growing. Some have fertilizer mixed in, and some say they retain moisture. Soil-based mixes are heavier and hold more water. Soil-less mixes are lighter, dry out faster, and are made with perlite and/or peat moss. You don’t have to buy the most expensive brand, but do buy one made for container growing. Look for a blend with nutrients listed and notice whether or not moisture retention is a feature. You do not need to add compost or sand, but it doesn’t hurt. Make sure the compost is sterile. See above about and builder’s sand; it can harden if you use too much.
If your bagged soil says it retains moisture, you may need to adjust your watering, but keep in mind that containers can dry out fast, particularly in hot, sunny areas. Some containers may need daily watering, or even more often in the hottest part of the summer. Watch how the plants behave and test the soil to a depth of 2 inches or so to determine if more water is needed.
Select compatible plants; that is, plants that have similar sun and water needs. After planting, add a layer of mulch and slow-release fertilizer. Read the fertilizer directions to see how often you need to repeat fertilizing. It’s better to under-fertilize than over-fertilize, so a slow-release type is a good choice. Don’t stack mulch against the plant stems. Plants needs room for air to circulate.
Selecting plants is fun and allows experimentation with color and texture combinations. Mix practical vegetables with showy flowers for interesting effects. And there are plenty of pretty vegetables and herbs to pick from too.
Books on container planting are abundant. Some you might want to consider are:
- Square Foot Gardening by Mel Bartholomew — also they have a great Square Foot Gardening website.
- Pots in the Garden by Ray Rogers
- The Practical Encyclopedia of Container Gardening: Indoors and Outdoors by Stephanie Donaldson
- Can’t Miss Container Gardening by Felder Rushing
These books and many other container gardening books are available in the library at Lewis Ginter Botanical Garden.