The weather will direct your efforts in the vegetable garden in September. Frost may strike even the mildest of regions before the end of the month.
Know the average first frost date for your area. This date will allow you to plan your garden activities and prepare for cold weather in advance. The average first frost date can vary from year to year but when the first frost comes your warm-weather crops will be done for the year unless you take steps to protect them and extend their season. Check with a nearby garden center, master gardener program, or your county agriculture commissioner’s office to learn the average first frost date in your region.
Regional Gardening Suggestions for September
These suggestions are divided into 4 major geographical areas: North and East and Midwest (zone 2 in the northernmost areas to zone 6 along the Atlantic coast), the South (zones 7 in the north to zone 10 in the far south), the Southwest and California (zones 7 in the coolest areas to zone 11), and the Northwest (zones 5 in the highest elevations to 8 along the coast).
North and East and Midwest
Frost is possible in some areas before the end of September. Check the number of frost-free days left in your area by counting back from the average first frost date for your region. You may have time to sow quick maturing crops without protection. Plant fall salad greens such as spinach, winter lettuce, arugula, mâche, corn salad, mustard, and radishes. Use a cold frame or plastic tunnel if time is short. Plant next year’s garlic crop and divide multiplier onions. You can leave root crops in the ground until a serious freeze; parsnips taste best when exposed to frost. In the cold frame, sow parsley, lettuce, spinach, and chives. Parsley can be grown indoors during winter. Clean cold frames and line with straw before planting. Sow a green manure cover crop in vegetable beds that are done for the season.
Some very hot weather is still possible. Plant autumn salad greens now: leaf lettuce, Romaine lettuce, and mesclun. Plant as many greens this month as needed. Greens prefer rich soil, so apply plenty of compost. Plant hardy winter vegetables now in the Upper South: beets, Brussels sprouts, carrots, chard, cress, corn salad, kale, kohlrabi, onion sets, spinach, radishes, rape, turnips, leeks, mustard, and lettuce. Be prepared to cover plants if a hard frost is expected; cover plants quickly with hay or grass or cloches. In the Lower South plant bush snap beans, cabbage, cauliflower, celery, collards, endive, lettuce, onions, parsley, Irish potatoes, rutabagas, and turnip. Also, plant sweet potatoes now for spring use. In frost-free regions such as Florida, continue to plant warm-season crops such as tomatoes.
Southwest and California
Hot and dry weather can continue for several more weeks. Your “second spring” planting season begins in late September in the warm-winter regions of California and the Southwest. Plant seeds of broccoli, cabbage, and cauliflower in flats; these young plants will be ready to transplant into the garden as summer vegetables come out of the garden. Plant beets, bush beans, carrots, chard, Chinese greens, endive, kale, leek, lettuce, mustard, early onions, parsnips, potatoes, winter radishes, spinach, and turnips. Set out starts: cabbage, cauliflower, Italian sprouting broccoli, kale, kohlrabi, Romaine and leaf lettuce, late potatoes, salsify, and late spinach. Garden peas can be planted now, but shade them if the weather continues hot. When nighttime temperatures drop below 50ºF the garden slows and when the temperatures drop below 40ºF the garden will approach dormancy, but in warmer temperatures and where there are few freezing days each year you can garden on. In regions where frost will come before plants mature prepare portable cold frames and tunnels to cover crops after the first freeze. In most regions, protected winter gardening is quite doable.
The weather will vary and can be unpredictable. Be sure to check the number of frostless days left in your area. Check seed packets and choose “fall” and “late” varieties; they are quicker maturing plants. Sow radishes and spinach. Set out starts of late cabbage, cauliflower, Brussels sprouts, broccoli. Divide rhubarb clumps now; leave one or two eyes per root. Clean the garden of debris as you complete your harvest. Continue to sow or set out vegetables that will reach maturity before the first hard frost; these winter harvest crops can be maintained and harvested with protection well into winter.
Additional Tips for September
September Harvest. Tender vegetables such as tomatoes, peppers, winter squash, and pumpkins must be picked before the first frost. Harvest broccoli, cabbage, cauliflower, and kohlrabi when they’re ready. If not picked, these crops must be covered on freezing nights. Remove the bottom leaves from the lanky stems of Brussels sprouts to direct energy to the sprouts. Potatoes, onions, turnips, carrots, and other root crops should be lifted before the ground freezes. Kale tastes best harvested after the first frost. Harvest and store green tomatoes before the first frost. Bring unripe tomatoes indoors to ripen; hang plants upside-down in a cool cellar or attic, where the fruit will ripen and can be used well into fall. Save seed from heirloom beans, tomatoes, squash, and melons.
Extend the Season. From the date of the first frost, autumn and winter gardening will go undercover; use cloches, plastic tunnels, and cold frames to extend your growing season. Protecting crops from cold temperatures will allow you to stretch the harvest and set out new crops in autumn and winter. Use plastic tunnels and cold frames to grow leafy and root crops through the winter.
Second Spring Planting Season. If you live in a frost-free or nearly frost-free region, the “second spring planting season” will arrive later this month. In the second spring season, plant the same cool-season leafy and root crops you planted in spring. In regions where the weather chills but never drops to freezing cool-weather crops can go back into the garden and your second spring will begin.
Fruit Trees. Harvest ripe apples, pears, and other late fruits, then freeze or can them. Rake dropped fruit and leaves up under fruit trees to disrupt the life cycles of pests. Mow tall grass and weeds in orchards. Wrap trunks of young trees to prevent sunscald. Place mouse guards around the trunks of young trees. Mulch trees in a ring 8-12 inches (20-30cm) from the trunk before the ground freezes. Watch for pests and signs of disease.
Grapes and Berries. Pick grapes only when ripe and only in dry weather. Too much handling destroys the grape’s protective bloom. Cut back old bramble canes and mulch them. Tie in new fruiting canes of blackberries and loganberries. Set out new strawberry plants.
Order Bare-Root Fruit Trees. Apples, pears, peaches, plums, and grapes may be ordered now for delivery in time for spring planting.
Asparagus Maintenance. After asparagus stalks have turned yellow, cut them off at ground level and apply a cover of well-rotted manure.
Garden Clean-Up. Clean the garden after crops have been removed. Plant debris left in the garden over winter can harbor pests and diseases that will emerge in spring. Clean the garden.
Amend the Soil. Dig compost or commercial organic planting mix into the soil wherever the last crops have come out. Top dress the garden with aged manure or plant a green manure cover crop such as buckwheat, annual ryegrass, or winter rye as soon as possible.
Green manure. If you do not plan to keep the kitchen garden growing with cool-season crops during autumn and winter, consider planting the beds with a green-manure cover crop. Green manures or cover crops add organic matter to the soil; they are tilled or turned under before they flower. Cover crop roots keep the soil loose, moist and aerated when vegetables are not in the garden. They also protect the soil from winter rains and erosion and add nutrients to the soil–thus green manure.
Green manure cover crops include annual rye or ryegrass, buckwheat, and winter rye. Other excellent cover crops come from the legume family: clovers, vetches, and alfalfa. The roots of legumes add residual nitrogen to the soil which will benefit vegetables and herbs growing in the garden next season.
Make Compost. Select a spot for a garden compost pile. Compost can be made of alternate layers of garden and vegetable refuse, soil, and manure. The bottom layer should be 6 inches (15cm) thick; use coarse materials such as shrub prunings, corn stalks, and straw. Top this with 4 inches (10cm) of cow or horse manure; cover with 4 inches (10cm) of soil plus the same amount of leaves, lawn cuttings, weeds, and vegetable tops, mixed together. Avoid using pest or disease-infected cuttings. Keep the top concave so it will retain rainwater or wet the pile down every ten days during warm weather. Turn the compost pile occasionally to add air to the mix. Rich humus compost should be ready in about 9 months with no additional effort.
Container Gardens. Harvest vegetables and herbs from containers. When the plants are spent or killed by frost, remove the plants and compost them. Clean and disinfect the containers before storing them for winter.