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Now we're entering a period of warm, dry weather. What should we be looking for in gardens? Care for container plantings. The baby plants installed on decks and patios in May have matured into billowy masses by now, and are in full bloom. Many can look good right up to frost if they get proper care in July and August.
All plants in containers need careful, regular watering in hot weather. The type of plant and the type of container influence how rapidly water is absorbed and how warm the soil gets. If the container is dark green, brown, or black plastic, facing a hot western or southern location, soil can heat up rapidly and roots will be killed by heat. If the plant's in a black nursery pot, waiting to be settled in a permanent place in the garden, be sure to protect the pot from direct sun.
Plastic pots come in nearly infinite types, some of them masquerading very nicely as terra cotta. They're affordable, lasting, and effective. Check the bottoms of the pots to be sure drainage works (holes should not be plugged.) Plastic pots retain moisture well, but still need regular watering in hot weather. One plastic type to avoid is the kind with the attached saucers. Container plants mustn't stand in water unless they are specifically water plants such as water lilies. Take off the saucers, even if the tidiness of their appearance appeals!
On a wooden deck, raise container plants off the wood to allow air circulation underneath. (Pot ‘feet', some of them cute, like frogs, are sold. Bricks work, too.) Some pots come with lower rims that do allow some air to move. Lift pots frequently to let the deck wood dry thoroughly. (Simply shifting them to one side works fine.) One of my most startling experiences in landscaping happened when I moved a client's large pot and the deck underneath it immediately collapsed from rot.
Water containers early in the morning or in evening. Fertilizer, regularly applied, also helps keep container plants in good health. Use any liquid fertilizer. To encourage blooming, do not use a fertilizer with a high nitrogen level in mid-summer. Nitrogen is listed first on fertilizer labels, and always includes a number that represents the available parts of the nutrient in the mix. Summer annuals do well with a 5 or 8 ratio nitrogen. If the plant is over-fertilized with a high level, such as a 20 or 30 nitrogen, blooming will be reduced. The plant will produce bountiful green leaves and fewer buds. I prefer liquid fertilizers that list ‘trace elements' such as copper and manganese. Plants in containers need these elements.
Apply fertilizer faithfully every two or three weeks. This practice is particularly necessary in hot weather, because frequent watering leaches nutrients from container plantings. Water the plant first, allow it to drain, and then fertilize. Don't put fertilizer on a dry soil, even if it's a liquid formulation.
Finally, to keep container plantings thriving and blooming, remove old, spent flowers. Sometimes the plant will help you: impatiens and fibrous begonias are mostly ‘self-cleaning,' dropping their old flowers tidily. But most annual seedheads hang on. Pansies and petunias must have the withered flowers picked off. Old flowers on these two plants, and on geranium, tend to get a fungal disease called ‘botrytis' in damp weather, or where the foliage is crowded and stays wet from watering. Botrytis causes a gray, fuzzy mold to overwhelm the flowers and move to the leaves. Clean these out to keep the plants healthy.
Seed pods that form on annual flowers will cause the plant to stop blooming. Seeds, for an annual, mean that it's fulfilled the botanical destiny to reproduce. The next generation is ready to take over. Why would it need to continue blooming? Check under leaves and deep in plants for hidden seed capsules.
Caring for container plants is the ‘light duty' of gardens, and can result in good bloom and great satisfaction for the next three months.
Hortsense: Managing plant problems with Integrated Pest Management
