What to do in your garden in July
• Butterfly plants. To attract butterflies to your garden, plant their favorite nectar-producing flowers, such as asters, bee balm, butterfly bush, butterfly weed, cosmos, gaillardia, marigold, rabbitbrush, shrubby potentilla, sunflower, verbena, and zinnia. Place bowls of cut fruit around the garden for species that feed on fruit.
Encourage butterflies to lay eggs by growing caterpillar-host plants, including aspen, chokecherry, dill, fennel, hollyhock, ornamental grasses, parsley, and sunflower. Usually their numbers are too small to harm ornamentals, but caterpillars may occasionally damage fruit, shrubs, and vegetables. To learn how to distinguish between desirable caterpillars and pests, call your local cooperative extension service (in the government pages of the phone book).
• Container gardens. When cool-season annuals such as clarkia, Iceland poppy, and stock stop blooming, replace them with heat-loving angelonia, bidens, bush strawflower, creeping zinnia, cuphea, floss flower, ground morning glory, marguerite (Argyranthemum frutescens), pimpernel hybrids, or scaveola. Check the soil twice daily and water when dry; fertilize weekly. Rotate pots periodically so sunlight reaches all sides. Remove faded blossoms to prevent them from setting seed and to ensure continued flower production. Cut back stems by half if they become long and leggy.
• Gaps in plantings. Spring-blooming perennials, such as bleeding heart, fernleaf peony (Paeonia tenuifolia), spring vetchling (Lathyrus vernus), Oriental poppy, shooting star, Solomon's seal, and Thermopsis, go dormant by midsummer. Cut off the foliage when it turns yellow and plug container-grown annuals into the empty spaces, taking care not to disturb the roots of the slumbering perennials.
• Madagascar periwinkle. For a burst of color that's impervious to summer heat, plant Madagascar periwinkle (Catharanthus roseus), sometimes called annual vinca. Its heat resistance and long summer bloom make it a good replacement for annual phlox, whose flowers look similar. Colors include lavender, peach, red, rose, and white; most have a contrasting eye. Choose trailing varieties, such as those in the Carpet and Mediterranean series, to spill out of baskets and pots. Plant in well-drained soil and allow the soil to go almost dry between waterings.
• Pest outbreaks. Using a hose-end attachment, knock aphids, juniper spittlebugs, spider mites, and thrips off plant leaves and stems with a strong stream of water. Hit all surfaces, including the undersides of leaves. To help control powdery mildew, spray susceptible plants (dahlias, phlox, roses) with water every few days. Water doesn't eliminate pests completely, but it keeps their numbers from reaching plague proportions.
• Weed killer damage. Avoid applying weed killer during hot or windy weather. Chemicals volatize at high temperatures, and wind can carry the spray to adjacent areas, causing damage to untargeted plants. Follow label instructions.