It's tempting to think of container gardening as instant gardening because the planting process is so fast and easy. Choose a container and the plants you want to grow, add potting soil and water, and you're ready to go. However, plants grown in containers do have several special needs, because the small space and volume of soil in which the roots grow limit the amount of nutrients and water available. To help your container plants grow their best, it is important to use high-quality potting soil that allows for vigorous root growth, appropriate fertilizer to encourage healthy foliage and abundant flowering, and proper watering techniques that never leave plants parched and dry or drown them.
Potting Soils
Plants growing in containers need quick-draining, fluffy, light soil. Garden soil and commercial topsoil intended for use in garden beds are too heavy, and plant roots will not thrive in them. The easiest route is to buy container potting soil, although you can also mix it yourself.
Packaged potting soil is readily available and is sold in bags ranging from 5-50 lb (2.3-22.7 kg). There are differences in quality and price among brands, but you should buy the best you can afford. Begin at a nursery or garden center, and ask for the best potting soil available. Try out a small bag. When you find a product you like, you can buy it in larger quantities, usually at a discount.
Whether you buy it or mix your own, the potting soil should be a fine-tuned mixture of peat moss, compost, and a little sand, with small amounts of puffy white perlite or flaky vermiculite added to lighten the mix and aid drainage. Some warning signs of poor-quality potting soil are a clumping, claylike consistency, numerous wood chips or sticks, an extremely gritty feel, and color that is either gray or light brown rather than dark brown to black.
In recent years, many potting-soil manufacturers have begun adding fertilizer to their mixes. Potting soils that include fertilizer simplify the planting process, because you don't need to mix in fertilizer as you plant or begin feeding plants for several weeks after planting. However, potting soils without added fertilizers are still a good value, and it's easy to sprinkle in small amounts of a balanced granular fertilizer as you fill pots with potting soil or begin fertilizing after planting with a water-soluble formula.
If you want to mix your own potting soil, fill a large bucket or wheelbarrow with two-thirds compost that has been screened to remove sticks, stones, and clumps. The remaining one-third should be a combination of peat moss and either perlite or vermiculite, which are available at any garden center or nursery (wear a dust mask when mixing in these dusty ingredients). Stir the mixture together to combine all ingredients and you're ready to plant.
Spread a layer of pebbles or pot shards over the drain holes of a container to keep soil in while letting excess water drain out. Then add soil until the pot is about three-quarters full. Shake or rock the pot gently to help settle the soil, and place the root balls of your plants on the soil, building it up as needed so that the base of each plant is just below the rim of the pot. Continue filling soil in around the plants and shaking until the soil reaches 1 in (2.5 cm) from the pot rim; if you plan to top the soil with an ornamental mulch, fill to 2 in (5.1 cm) of the rim. The soil should not "shrink" too much if you've shaken the pot and covered the drain holes properly. Large containers should be placed in their final position before being filled, so that they won't have to be moved when heavy with soil. Some gardeners also like to soak terra-cotta, stone, or cement planters in water before filling them, so that the container does not wick moisture out of the soil.
Feeding Container Plants
The roots of container-grown plants cannot wander far and wide in search of nutrients, so it's up to you to supply them. Even if you start with potting soil that contains fertilizer, those nutrients will be gone in a matter of weeks. Plants will use some of them, and the rest will be flushed out when you water.
There are two easy ways to keep container-grown plants well fed. You can dose them with water-soluble plant food, which is a liquid or granular food that is mixed into the water used to irrigate plants. Apply this liquid fertilizer full strength according to the package directions, usually every 10-14 days. Some gardeners prefer to use the fertilizer at half the strength but twice as often.
You can also scratch small amounts of a balanced organic fertilizer into the soil surface every 6-8 weeks. For plants that will remain in the containers for a long rime, as opposed to seasonal displays, use a commercial controlled-release fertilizer, which has a coating that breaks down gradually depending on temperature and moisture.
Plants vary in their nutritional needs, so there is no fixed feeding schedule that suits all plants. However, because container plants are easy to monitor, you can usually tell when they are not getting enough nutrients. Slow growth, yellow leaves, and poor flowering are the most common signs of nutritional deficiency. If plants quickly improve after being drenched with a liquid fertilizer, you will know for certain that you underestimated their appetites. Still, be careful not to overdo it, or your plants may develop browned leaf edges, a symptom of fertilizer burn. To safeguard against this problem, never exceed the application rates given on the fertilizer label.
Watering Strategies
All plants grown in containers require regular watering, and their need for water increases as they gain size. When plants are small, you can usually do a good job of watering them with a watering can equipped with a sprinkle head, or rose, or a hose equipped with a watering wand. These perforated watering heads reduce water pressure while breaking up the stream into a gentle flow that soaks into the soil without dislodging delicate plants. But after the root system becomes extensive, watering becomes more challenging. Instead of soaking into the soil around the roots, water may run over the top of the soil and seep down through a gap that often develops between the soil and the pot. Sometimes it runs off the surface of the soil, so that even though you water, the root ball may remain dry. It is a common mistake to think that the plant does not need water when this happens. You can tell when this is happening by watching how much water seeps
through the drain holes and by testing the pot for weight. If you tip the pot and it seems no heavier than before you watered, it's time to take action. The best way to know for sure, however, is to stick your finger into the soil. If the soil feels dry up to the first knuckle on your finger, then the soil definitely needs to be well watered.
The first remedy is to water with warm water, which soaks into dry soil much faster than cold.Then poke small holes into the soil's surface with an ice pick, pencil, or screwdriver. Water thoroughly, sprinkle in enough fresh potting soil to fill the gap just inside the rim of the pot, and water again.
Another solution is to place the pot into a large tub and fill with warm water up to the pot rim. Let the soil soak up water from beneath for about a half hour, then drain.This is often the best way to revive plants that have dried out completely. If the problem persists despite your efforts, you will need to repot the plant into a larger container.
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