Q. What are some annuals that can tolerate the summer heat?
A. Celosia (cockscomb), gallardia (blanket flower), gomphrena (globe amaranth), African marigold (Tagetes erecta), portulaca, torenia, zinnia, and verbena are annuals that can tolerate heat. For a low splash of color comparable to impatiens and wax begonias, the verbena would come the closest. All summer annuals suffer to some extent as heat, humidity and insect populations are at their height during the season.
Q. What all-around fertilizer can I use for my annuals?
A. You can get by with a monthly fertilization with Peters 20-20-20 liquid soluble fertilizer or one application of Dynamite. Water annuals about twice a week after they are established.
Q. What do commercial seed growers do for good germination of seeds? The seeds collected in my yard, mainly marigolds, do not have a high rate of germination.
A. Most annuals from seeds nowadays are hybrids or tetraploids. They often are either sterile or produce only a little viable seed. For best germination, you would have to specify old varieties that have not been so highly bred. Your germination rate should be better then. Marigolds are best germinated in an indirect light location _ the north side of the house under a shade tree. After that they can be gradually moved out to a full sun location. Seedlings may suffer from damping off, which is a fungal condition that causes them to collapse from rot at the base of the stem. Keep seedlings in an area where there is good air movement.
Q. Where can I get seeds for ornamental cabbage and New Guinea impatiens?
A. Ornamental cabbage should grow here in the coolest part of the year between December and March. Seeds for ornamental cabbage and New Guinea impatiens, a more sun-tolerant variety of impatiens, are available through Parks Seed (See Supplier's list).
Q. What can I plant under a silk oak tree? I was considering impatiens.
A. I would not damage the feeder roots of the silk oak for impatiens. Consider using a more permanent plant like pentas, which will last about three years in the ground and is more aggressive and larger than impatiens. It blooms all the time and is a durable cut flower lasting a week or more in water. The silk oak likes dry conditions and impatiens needs a lot of water, so it is important to choose this planting to avoid root rot on the silk oak.
Q. I am having trouble with my impatiens, which I purchased from different shops. They seem to die overnight and the bottoms come off. What care do they require?
A. Your soil is infected with a fungal disease, which is killing the plants. Treat the soil with Subdue; it may bring some relief, but there is no guarantee. The plants also may have been infected at the nursery. Impatiens are annuals planted in October and finishing up in April and May. They need shade for an extended growing season. They use a lot of water and excessive water can cause root rot and kill permanent plantings. Plant the impatiens in a large bonsai pot with sterilized soil.
Q. What ideas do you have to replace impatiens as bedding plants?
A. For your bedding plants, substitute something like wax begonia and red salvia for winter and torenia and marigolds for summer, which need watering only about twice a week instead of daily. "New Look" pentas and purple weeping salvia are new perennials that show good promise.
Q. My garden up north had dusty miller. Can I plant it here?
A. Dusty miller is a variety of artemesia with beautiful silvery foliage. The summer heat and rainfall can do them in, particularly if an irrigation system is nearby. They like a sunny, well-drained location where they will not receive a lot of water. They are used as bedding plants or a border. The silvery leaves contrast beautifully with pink geraniums, which like similar growing conditions. They also look good with yellow or red blooms. I would treat them as annuals here. Plant in October and figure them to fade away by May. If you can plant them in a raised bed with good drainage they may go over the summer. Dusty miller is salt tolerant and a nice accent for oceanfront condominiums. The form we grow here is sencio.
Q. How do we care for portulaca?
A. Portulacas are summer annuals that like sunny dry locations. In wet years they are much more likely to get leggy and rot. The Purslane is similar and lasts longer in the landscape under dry conditions.
Q. I planted periwinkles, New Guinea impatiens and other annuals, spread a layer of mulch and have watered them diligently but they are dying. What did I do wrong?
A. Overwatering causes periwinkles to die from fungal disease. Once established they do not want any extra water. The New Guinea impatiens can tolerate more sun than the regular impatiens, but they are still delicate.
Q. Can I plant castor bean in South Florida?
A. The red-leafed castor plant, which has poisonous seeds, sometimesis used as a bedding plant in Europe because of the tropical foliage. Grow it if you like but consider it weedy and a bit dangerous.
Q. My globe amaranth has eggs on it from a fly-like insect. The plants seem to die off. What is happening?
A. The globe amaranth is a summer annual that will fade at the end of the wet season in October. I would remove the plants. I suspect your insect is a stem borer, which is hard to control with a conventional spray. It can also attack marigolds