Container Gardening 2 – What Goes into the Pot?

By Elizabeth Cornell Fake, Fairfax Master Gardener
In Part 1 of this series on container gardening, we looked at choosing suitable pots, taking into account site, size and style. (See Container Gardening.) The next step — and the focus of this article — is what to put into the container. While container-gardening websites and blogs offer an infinite amount of advice on the subject, here we will look at the importance of drainage and soil.

Drainage

holes in pot

Drainage holes are essential to container gardening

Say you have selected a tall, ceramic pot with good thermal insulation for a full-sun site. Looking down into your empty pot, think about drainage first. Normally your container will have a 1-inch hole in the center of the bottom. The drainage hole allows surplus water to drain out of the pot, creates air circulation and keeps the plant roots from drowning in too much water. If your pot doesn’t have a hole, make one by drilling a small hole in the bottom. If you are using a liner inside another container, make sure the liner has holes in the bottom.

Many container gardeners insist they need some kind of fine gravel, clay shards or foam peanuts in the bottom of the pot to allow for proper drainage. But if you observed the process, you would see that water flows easily through fine material but pools around pieces of gravel or clay. The water isn’t flowing out of the pot; it is trapped within. The major benefit of gravel is to help keep the soil in the pot from flowing out of the drain hole. But it doesn’t enhance drainage. Since we are trying to avoid having plants with “wet feet,” forego the gravel, and use a fine-plastic or wire mesh at the bottom of the pot to keep the soil inside.

Soil

Your first thought might be, “I’ll just use some of the same soil I’m using in my other gardens for the container.” Although your flowers and vegetables may be flourishing in the mixture you have concocted for your garden plot, it will not be the best mix for a container. Container gardens need soil that is well-aerated and allows drainage but also retains adequate moisture and nutrients necessary for plant growth. Most garden soil is much too compact for containers and limits air circulation.

Commercially prepared potting soils, or potting mixes, are the best choice for a container. Potting soil is not dirt, but it does contain non-soil “media” such as perlite, vermiculite, calcined clay (kitty litter), sphagnum peat moss, bark or coconut fiber, which allows drainage and air circulation. It is prepared under laboratory conditions, sterilized and free from insects, weeds and diseases. Choose a good potting soil from a garden-supply store, and gently pile it into the container without tamping it down. Make sure you leave plenty of space for air circulation and leave about an inch at the top of the container to allow space for planting later.

Next month we will discuss the plants to put in containers — the thrill, fill and spill of it all.

More Information
Successful Container Gardens, University of Illinois Extension
How do I Ensure Good Drainage in Container Gardens?, HGTV
Using Soil In Gardens: Difference Between Topsoil And Potting Soil, Gardening Know How

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