Build Your Own Inexpensive Container Soil
We typically have a dozen or more containers of various shapes and sizes on our deck and by the front door. Almost all of the plants in these containers do quite well, in part because I rebuild the soil each year. Here’s a recipe for a planting mix for your containers that is easy and inexpensive.
The initial fill for all of our containers is a combination of bagged topsoil ($1.50 per cubic foot) and peat-based planting mix ($4.00 per cubic foot.) I prefer a mix without fertilizer added so I can control the food to the plants myself. Dump equal parts into a wheelbarrow or bucket, mix together, and fill each container to the brim. Then mix some additional soil to fill an extra bucket or two.
Bagged topsoil is consistent in texture and reasonably weed-free. Peat-based planting mix is lighter than topsoil, and adds the water retention capability all containers need. The combination has enough weight to anchor your plants, but is light enough for roots to grow uninhibited.
Put your containers outside in their normal locations and water well. The soil will settle a bit. Top off with material from the buckets before planting.
Plant your flowers or vegetables or herbs at the depth they were growing in the nursery packs, then scratch some fertilizer into the top half inch or so of soil. Slow release fertilizers are best: the nutrients won’t get washed out of the container with frequent waterings. Fertilize again monthly throughout the season.
All my container plants are annuals, so at the end of the year I pull out the dead plants and store the soil-filled containers in the garage. In April I put on some old clothes and dump the containers into a wheelbarrow, pulling out any stray stems and roots still there. Then I add about 25 percent by volume more peat-based planting mix (no additional topsoil is added.) This keeps the soil light for good root growth year after year.
This system has one minor drawback. Many of my container plants are Wave® type petunias that flower profusely. Many flowers translate to lots of seeds. These seeds are still in the soil when the containers are stored for the winter, so they are also in the soil used to refill the pots in the spring. I’ve planted 1 petunia in a 15 inch pot only to have a couple hundred volunteers germinate afterwards from last year’s seeds. These seedlings can be easily disturbed by scratching the surface of the soil with a hand cultivator. Or use a germination inhibitor at planting time. Remember that if last year’s plant was a hybrid, this year’s seedlings will not be anywhere near as good as the original.
Unglazed clay pots and coconut fiber containers will dry out a lot more rapidly than plastic or ceramic ones, so you’ll have to water them more often. If you are spending too much time watering all your containers consider installing a drip irrigation system, or use containers with water reservoirs.
Try these tips to make your containers even better this year.
Jim Janke is an Extension Master Gardener Volunteer in Haywood County. For more information call the Haywood County Extension Center at 828-456-3575. © 2013 NC State University.