Vegetable crops will begin to take longer to ripen in September. Give melons, limas, and tomatoes more time to ripen naturally. Eggplants are ready for harvest when they are shiny.
Beans, cucumbers, melons, zucchini, and summer squash will not ripen or mature once they are picked. They will keep for a week or two in the refrigerator.
Large cabbages and broccoli side shoots will come to harvest in cooler regions. Cut-and-come again harvest of lettuce, spinach, and greens will stimulate new fall growth.
Dig regular potatoes and sweet potatoes as late as possible, just before frost threatens. Pick all tomatoes, peppers, beans, vine crops, winter squashes, and other tender vegetables before the first hard frost.
Planting in September. In mild-winter region planting, cool-season vegetables can be planted in September. Plant now beets, broccoli, Brussels sprouts, carrots, cauliflower, celery, fava beans, kale, kohlrabi, leeks, both head and leaf lettuce, mustard greens, onions, parsley, peas, potatoes, radishes, rutabagas, spinach, Swiss chard, and turnips.
Tomatoes. Pinch off the top of all tomato plants in September; remove at least six inches of foliage on each stem. Plucking away fruit-bearing foliage will allow the plant to put its strength into ripening tomatoes already on the vine.
After harvest, freeze tomatoes whole or sliced. Scald tomatoes for one minute then place them on oiled baking sheets in the freezer for one day. After freezing, the tomatoes can be bagged or boxed and returned to the freezer.
Peppers. Chili peppers ripen best on the vine; sweet peppers will ripen after picking. Sweet peppers left on the plant will keep fresh longer than those harvested. If you harvest peppers at the green stage, the plant will continue to set new fruit. To ripen sweet peppers out of the garden, lift the entire plant and hang it in a room or shed at 50°F (10°C).
Eggplant. Harvest eggplant when they are small; they are ready for use and most tender at one-third to half their mature size. Harvest an eggplant before its skin loses its shininess. Cut the fruits from plants with shears leaving some stem attached. Use eggplants shortly after harvest for the best flavor; they will keep one to two weeks at 50°F (10°C) after harvest.
Summer squash. Zucchini and straight neck and crookneck type summer squashes can be harvested at 4 to 5 inches (10-25cm) long; don’t let them sit in the garden too long and become seedy. Scallop and pattypan squashes are best small, no larger than 4 inches (10cm) across. Summer squashes will keep in the refrigerator for about two weeks.
Winter squash. Winter squash is ready for harvest when the skin is tough and the stems shrivel and dry. Cut them from the plant leaving 4 to 6 inches (10-15cm) of stem attached; fungi and bacteria can enter stored squashes if the stem is torn away. Leave winter squashes for winter storage on the vine until next month; rest fruits still in the garden on a piece of wood or brick to keep pests and disease at bay.
Shell beans. Leave shell bean plants in the garden until the pods become brown and dry. If wet weather comes, pull up the plants and hang them to dry by their roots in an airy shed or porch.
Potatoes. Maincrop potatoes are ready for harvest when the foliage begins to fade and some leaves turn brown. When leaves begin to fade, potato plants stop manufacturing food to feed the growth underground. Use a garden fork to gently loosen the soil then lift the tubers by hand. Let potatoes dry out for an hour or so on top of the ground; cure them at 55°F (13°C) for two weeks before storing. Store potatoes in a dark, cool well-ventilated place; place them in slotted boxes or bins or in baskets.
Sweet potatoes. Sweet potatoes are ready for harvest when the vines turn yellow and die or are killed by frost. The plants will stop growing at temperatures below 65°F (18°C); if exposed to temperatures below 50°F sweet potatoes will deteriorate rapidly. Lift sweet potatoes with a garden fork; let the roots sit in the sum for a day or two to cure; then place them in a shady area at about 80°F (26°C) for a week to 10 days. Cure sweet potatoes before you store them.
Rutabagas. Rutabagas can stay in the ground past one or two frosts but should come out of the garden before the soil freezes. Place rutabagas and other root crops in plastic bags with holes punched in them for air circulation. Place roots in the refrigerator crisper or a humid root cellar with the temperature just above freezing. Bagging will keep roots clean, provide a steady temperature, and seal in an even moisture level.
Carrots. Lift maincrop carrots with a garden fork and cut off the tops. Begin the harvest by lifting fingerlings which will be most tasty eaten right away. Use split root carrots as soon as possible as well. Winter store the remainder of the crop in layers in deep boxes, with ½ inch of sand between each layer. Place storage boxes in a dry shed.
Lettuce, spinach, and other greens. Keep lettuce, spinach, and other greens trimmed so that they will not bolt. Harvest greens cut-and-come-again, removing outside leaves first. To avoid looseleaf lettuce bolting where the weather, take a knife and slice off the whole head 1 inch (2.5cm) from the ground; you can get two, three, or four cuttings from a single plant each season using this method.
Shallot and onions. Harvest shallots when the tops are yellow and shriveled. Lift bulb onions after about half the leaves have fallen over (a third in warm regions). Before lifting bend over the tops that are still standing and let the bulbs ripen for three or four more days before lifting. Let them cure in the sun or a warm, dry place for a week; don’t store onions until the top and papery skins are dry and crinkly.
Cabbage. Plant spring cabbages in beds that have been amended with aged compost and manure. Where winters are wet, plant spring cabbages on ridges 9 inches (23cm) high. Add a pinch of bone meal into each hole at transplanting. Set the plants with their bottom leaves at soil level, firming them in with your heel and then watering.
Watering. Keep the garden watered in autumn; there is still plenty of warm weather coming and crops depend on soil moisture to make their final growth and ripen.
Protecting crops. Cloches or plastic tunnels will offer low-temperature protection for crops including lettuces, spring cabbages, broad beans, and carrots. Winter crop protection will reduce losses during winter and hasten maturity in spring. Put hoops in place now so that crops can be covered quickly when frost threatens.
Herbs. Sow parsley and chervil now for a spring crop. Divide and replant clumps of bergamot; about one foot apart, preferably in rich soil. Take cuttings of bay, lavender, and rue and root them in sandy soil in a shaded frame or cloche.
Cleanup. Begin garden cleanup as crops come out of the garden. Remove any plant debris that will allow pests and diseases to overwinter. Where there has been no disease or pest problem, the green residue can be turned under.
Recordkeeping. Update your garden map and note the dates of dates the final harvest. These notes will come in handy next year.