Every plant needs the right soil, water, light, and fertilizer, but container-grown plants need a little bit more attention from a caregiver than those grown in the ground. Here's our guide to success with potted plants.
Soil for Potted Plants
Container plants should be grown in a special potting mix that doesn't contain soil. Garden soil is too heavy and may compact roots, cutting off their oxygen. It also often contains weed seeds.
Make or buy a soilless mix -- one composed of peat moss or coconut fiber (coir), vermiculite or perlite, and other ingredients. A lightweight soil for potted plants needs to provide good drainage, hold moisture, and give roots room to grow.
Test Garden Tip: Most orchids are the exception to this rule. They need a potting medium that gives even better air circulation than the typical soilless mix. Bark chunks are used for potting some orchids, while other types need only a slatted wooden basket or a slab of wood.
Watering Potted Plants
Water and drainage play a key role in success with container plantings. Poor watering practices -- especially overwatering -- kill more potted plants than anything else.
One easy rule: Use room-temperature water when possible. Cold water can harm roots and foliage, and hot water can kill plants instantly. Also, allow tap water to sit for several hours to evaporate any dissolved chemicals. Softened water contains sodium that can accumulate in the soil and burn plant roots when used over time. Use an outdoor tap for plant water, or install a tap for watering plants before the point where the line enters the softener.
Watering plants in the morning allows any moisture on the foliage to evaporate before evening; foliage that remains cool and wet during evening and nighttime hours is more prone to disease. This is especially important for disease-prone plants such as tomatoes and roses.
Another must: Containers need drainage holes so plants are not left sitting in water. You can place saucers under pots to catch and hold rain or extra water, but remove any excess water left after about an hour to prevent root rot and excessive sogginess in the soil.
Before watering always check soil moisture by poking your finger into the soil. Only water if the soil feels dry. Wet soil can be tricky, because when roots drown and die, the overwatered plant often droops, making you think it needs more water. Checking the soil moisture prevents you from compounding the problem with even more water.
If a plant has dried out completely, submerge the pot in water to its rim to allow the soil to soak up moisture from the top and the bottom. Submerging is usually an easy way to water dried-out hanging plants as well; use a tub or sink, and leave the pot there until air bubbles have stopped appearing.
How often do you need to water? That depends on the type of plant, the size of the pot, the weather, and other factors. Outdoor containers might need watering as often as once or twice a day during hot, dry weather but much less during cooler, cloudy conditions. As a general rule, the larger the container for your potted plants, the less watering you'll need to do. The container material matters, too: A plant in a porous clay pot needs water more frequently than one in a plastic or ceramic pot.
Various types of plants have different watering requirements: Think about the differences between cacti, which prefer infrequent watering, and cannas, which prefer constantly moist soil. In general, plants with a lot of leaf surface or soft, lush foliage are thirstier than those with less foliage or waxy leaves. Plants with silver, fuzzy leaves also typically need less water.
A general rule: It is better to water less often and more deeply than to offer light, frequent waterings.
Outdoor containers, in general, should be at least 12 inches wide and 10 inches deep. The bigger the pot, the more room is available for roots, so the better your plants will perform.
Large potted plants need larger containers, and small ones should go into smaller containers. Mixed containers often look best when you use a large container and include graduated heights and variety in foliage texture.
All plants depend on light for their survival, and making sure your potted plants get the right amount of light is key to keeping them happy. For both indoor and outdoor containers, group plants with similar light requirements. Don't mix shade lovers with sun lovers in a single pot; one or both of them will be unhappy, depending on where you place the pot.
Fertilizing Potted Plants
Every time you water a potted plant, nutrients leach out of the drain holes along with the excess water. An easy way to deal with fertilization is to use time-release organic fertilizers. Soil microbes activate organic fertilizers, which slowly release their nutrients to plants.
Compost and rotted mature improve soil drainage and add nitrogen -- needed for healthy foliage -- and other nutrients. Other sources of nitrogen include blood meal, cottonseed meal, fish meal, and fish emulsion. Plants also need rock phosphate and potash.
Buy bags of premixed, balanced (the numbers on the bag should match, such as 10-10-10) organic fertilizer and use it in addition to organic amendments to build healthy soil for your pots. Follow label directions for amounts to use in containers. Feed when you plant, then monthly after that.