Annuals. Replace fading cool-season annuals with heat lovers. Zinnia Profusion is a favorite with Sunset's Garden staff because of its six months of bloom. Besides Cherry, Orange, and White, this year Profusion is available in Apricot and Fire (scarlet-orange). Other popular choices include ageratum, coleus, dahlias, marigolds, nicotiana, and phlox.
Container-grown roses. Buying roses in bloom is more expensive than bare-root, but it allows you to judge flower color, form, and fragrance. Nurseries are well-stocked with container-grown plants this month.
Dahlias and gladiolus. Coastal ( Sunset climate zones 22-24), inland (zones 18-21), and low-desert (zone 13) gardeners can plant dahlias now. In the high desert (zone 11), begin planting gladiolus. Want more choices than your nursery offers? Try www.easytogrowbulbs.com, a new mail-order source that specializes in bulbs for warm climates.
Vegetables. Coastal gardeners (zones 21-24) can continue to plant quick-maturing, cool-season crops like chard, leaf lettuces, and spinach. Inland (zones 18-21), switch to warm-season crops like beans, corn, cucumbers, eggplant, melons, peppers, pumpkins, squash, and tomatoes. In the high desert (zone 11), frost is still a possibility; wait a few more weeks. If you're looking for a seed source for Thai, Japanese, or other unusual eggplant, try Baker Creek Heirloom Seeds ( www.rareseeds.com or 417/924-8917). It sells more than 30 eggplant varieties.
Fertilize. Feed trees, shrubs, groundcovers, perennials, turf grasses, and other permanent ornamentals (as well as houseplants) that didn't get fertilizer last month.
Prune euphorbias. To keep E. characias and other commonly grown euphorbias from getting leggy, cut them back hard after their chartreuse blooms fade, suggests garden guru Mary McBride of Mary's Garden nursery in Vista. Plants will generate fresh foliage.
Treat for iron deficiency. If camellias, citrus, hibiscus, and other plants exhibit yellowing leaves with green veins at this time of year, it's a sign of iron deficiency. Feed plants with a fertilizer containing chelated iron.
Pests and Diseases
Powdery mildew. A common problem on rose foliage and other susceptible plants in spring, especially along the coast, this fungal disease can be difficult to manage. Control it by spraying leaves with a baking-soda formula: Add 1 tablespoon baking soda and 1 tablespoon canola oil to 1 gallon of water.
Rose pests. Rose slugs ― those caterpillar-like insect larvae that chomp and tatter rose leaves ― have been a huge problem in recent years, especially for coastal gardeners. Organic insecticidal sprays have little effect. Chemical pesticides like Sevin work, but they kill beneficial insects too. A new option is Spinosad, a pesticide derived from a soil bacterium. Rose slugs ingest it, which causes them to stop eating, then starve. Spinosad, the active ingredient in Monterey Garden Insect Spray (available from www.montereylawngarden.com or 559/499-2100), does not harm most beneficial insects.