Here is some timely advice from James Quinn, retired horticulture specialist for University of Missouri Extension.
Vegetables
The state fair in Sedalia can be an opportunity to see the award-winning vegetables and related displays, which are in the MO-Ag Building.
Plan now for a fall garden. Cool-season vegetables will thrive in the cooler nights of late summer and fall and are not sensitive to frost. Consider transplanting hardy Cole crops such as broccoli, cabbage, cauliflower and Chinese cabbage in early to mid-August for fall harvest, with transplants being four to six weeks old. Plant in late afternoon or early evening to reduce transplant shock. Seed turnips in late July and carrots and beets in mid-August. Plant the seeds slightly deeper than you would normally plant them in spring to improve moisture availability for germination and root growth and water immediately and well.
Many warm-season vegetables can be grown in late summer and fall, the easiest being snap beans. They should be seeded in late July to early August. Their vegetative growth will be during late summer heat and then the flowering will occur as cooler fall weather sets in, making them unlikely to drop flowers in higher heat. They mature in approximately 60 days. Since the last planting date for tomatoes, peppers, pumpkins, squash and cucumbers has passed, review the plants you already have and determine if they might benefit from additional or more regular watering, a side dress application of nitrogen, or an application of a fungicide or insecticide for a pest issue.
Trees
Newly planted trees and shrubs should continue to be watered thoroughly, once a week. In early July, apply final treatment for borers on hardwood trees and any desired fertilizers to trees and shrubs. Fertilizing late may cause lush growth that is apt to winter kill. Hot, dry weather is ideal for spider mite development. With spider mite damage, leaves may be speckled above and yellowed below. Evergreen needles appear dull gray-green to yellow or brown. Damage may be present even before webs are noticed. Fall webworms begin nest building near the ends of branches of infested trees. Prune off webs. Spray if defoliation becomes severe. Summer pruning of shade trees can be done now.
In early August, prune hedges for the last time this season. In the latter half of August, evergreens can be planted or transplanted to ensure good rooting before winter arrives. Water the plant and the planting site several days before moving.
Flowers
Prune climbing roses and rambler roses after bloom. Clean up infected leaves and continue fungicidal sprays as needed. Use any extra spray for hardy phlox to prevent powdery mildew. Fertilize container plants every two weeks with a water soluble solution. Keep deadheading spent annual flowers for continued bloom and deadhead perennials that have finished blooming. Cut back the foliage some to encourage tidier appearance. Plant zinnia seed by July 4 for late bloom in annual border. Divide bearded iris now. Discard old center sections and borer damaged parts. Replant so the tops of the rhizomes are just above ground. Don't pinch mums after mid-July or you may delay flowering. Divide and reset oriental poppies after flowering as the foliage dies. Spray hollies for leaf miner control.
In August, worn and leggy annuals can be cut back hard and fertilized. Feed mums, asters and other fall-blooming perennials for the last time. Roses should receive no further nitrogen fertilizer after Aug. 15. Madonna lilies, bleeding heart (Dicentra) and bloodroot (Sanguinaria) can be divided and replanted. If you want to grow big dahlia flowers, keep side shoots pinched off and plants watered and fertilized regularly. Happy gardening!
Peter Sutter is a life-long gardening enthusiast and a participant in the MU Extension's Callaway County Master Gardener Program. Gardening questions can be sent to [email protected].