Container Gardening Guide: Planting and Maintenance

Author: NGA Editors

Begin with Design

Both containers and plants come in a wide variety of colors and shapes; mix and match plants and pots to suit your learning garden goals…and style! If you want to introduce an artistic dimension to your container project, have students think about the shapes, textures, and colors of potential container plants and flowers. Do they envision a riot of color or soft, calming hues? Growth habit is another variable. Snapdragons are tall and spiky; others, like impatiens, form round mounds; and plants like lobelia are long and trailing. Coleus have striking foliage. Students might want a blend of plants with complementary or contrasting qualities. Or, they might keep it to just a couple of compelling companions: tall pole beans surrounded by cascading nasturtiums, for instance. Older students can conduct research on garden design to learn about basic principles before tackling their own creations.

Here are a few more articles to inspire your design:
Cylinder Gardening
Gardens Are for Everyone (accessible gardens)
Moss in the City: A Container Veggie Garden
Moss in the City: Containers of Colorful Flowers and Foliage

The Nitty Gritty

Choose appropriate potting soil. Good drainage is key. Since the roots of container-grown plants are confined and can't go searching for what they need, you need to provide them with the best possible conditions. Your precious plants should thrive in a soil mix that drains well, retains moisture like a sponge, and offers support and nutrients. Garden soil is generally too heavy for container plants and may contain diseases or pests that could get out of hand. (But that shouldn't stop your young scientists from experimenting with it! See our lesson, Container Garden Soil Investigations to try it out.) It's best to use purchased soil mixes for containers rather than garden soil. There are many commercial mixes; if you prefer to create your own, you can start by mixing potting soil, seed-starting mix, and compost in equal proportions, then adjust the proportions and add other materials to suit individual plants.

Prepare your plants. If you've purchased transplants or started your own seeds indoors, harden off the plants before popping them into their permanent homes. For seeds, follow sowing dates recommended on seed packets. You can move the planting date up by a week or two if you’re able to move your containers to a sheltered spot in case of a cold snap.

For perennials, it's a good idea to follow the suggested spacing. You can pack annuals a little more tightly than generally recommended to create a nice, full look.

Maintenance

Accessories We Recommend Saucers. Waterproof saucers catch overflow and protect surfaces. But don't let excess water sit in the saucer — it can lead to root rot and may attract breeding mosquitoes. Unglazed terra cotta saucers absorb water, and may not prevent damage to surfaces underneath — use glazed clay or plastic saucers instead. Wheeled caddies or dollies. Place large planters on caddies with casters so you can move them easily. Look for locking wheels that will keep planters from moving accidentally. Pot feet. Moisture collects under planters and can stain surfaces. Pot feet are small, often decorative devices that elevate planters off the surface they're sitting on. Air circulating under the pot prevents moisture buildup, discouraging mold and algae growth.

Watering. The main difference between container and garden plantings is that you'll need to water containers more often. Closely spaced plants packed into a small volume of soil need watering as often twice a day in hot, sunny, dry weather. Water when the soil feels dry a couple of inches down, and be sure to saturate all the soil in the pot, not just around the edges. Water to draining from the bottom indicates that moisture has penetrated deeply; this encourages deep root growth and helps to wash away built up fertilizer salts. Pots that dry out very quickly may be too crowded; remove some, prune the rest back, or move the pot to a location out of direct sun and wind. If you have a lot of pots, consider installing a simple drip irrigation system to give students (and teachers!) more time to focus on learning and less on maintenance. Mulch on the soil surface also reduces moisture loss.

Fertilizing. Because their roots are confined and can't go searching for nutrients, you'll need to feed container plants regularly. Rapid growth and frequent watering remove the reservoir of nutrients quickly, so fertilizing is a critical task. One option is to mix slow-release fertilizer pellets and/or compost into the potting soil according to package instructions. You can also add additional nutrients throughout the growing season by dissolving a water-soluble fertilizer in the watering can once every week or two. Consider mulching with compost and using organic fertilizers such as compost tea, fish emulsion, or liquid seaweed. Your keen observers may want to try some different fertilizers and schedules, collect data, and try to explain their results.

Grooming. Keep plants looking lush and full by removing spent flowers, pruning leggy stems back to buds or branches, and removing off-colored and damaged foliage. Many plants continue to produce new flowers if you remove the spent blooms before they set seeds. Pinch the flower stems back to just above a leaf or bud.

Monitoring for pests and diseases. While container-grown plants can be less vulnerable to pests and diseases because they receive extra attention and pampering, you should still examine the foliage, flowers, and fruit regularly. Some insects, such as aphids, can be kept in check by simply hosing them off the plants every few days. Research your pest and disease problems before taking action to be sure you’re choosing an effective control. See NGA’s Pest Control Library for ideas.

Change plants seasonally. When the plants begin to look tired and past their prime, pull them out and replace them with fresh ones. You can keep your container current with seasonal themes by growing a succession of plants, such as bulbs and primroses in the spring, annuals and vegetables in the summer, and colorful kale and pansies in autumn.

Prepare for winter. In cold climates, containers and their contents need protection from freezing temperatures. Even hardy perennials, trees, and shrubs cannot tolerate completely frozen roots. Wrap chicken wire around the pots of small trees and shrubs and stuff with loose mulch, such as straw. Store in an unheated but not freezing garage or basement for the winter.

Terra cotta and ceramic pots may crack if left outside to freeze. Empty their contents into the compost pile and store the dry pots in a protected garage or cellar.

 

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