Gordon Johnson, Extension Vegetable & Fruit Specialist;gcjohn@udel.edu
The following are latest planting dates for unprotected culture of vegetable crops on Delmarva:
For cucumbers (pickles and slicers), the latest planting date for Delmarva should be August 7. Experience has shown that after that date yields drop considerably. With summer squash, late plantings can be made until August 10.
Snap bean crops can be planted up to August 10.
Cole crop planting for fall harvest using transplants continues. Broccoli is transplanted up to August 20, cabbage up to August 10, and cauliflower up to August 10.
Kale and collards should be seeded before August 15 for best yields, transplants can go in up to August 30. Turnips and mustard greens can be planted from late July through the first week in September.
Beets are best planted before August 10 for roots, by August 20 for greens.
Green onions should be planted by the end of August for fall harvest. Overwintering green onions can be planted through October using hardy varieties.
Bulbing onions for overwintering should be seeded from September 1 through September 15 using overwintering specific varieties. Bolting will be a problem if planted too early. If using transplants, planting should not take place until October. Leeks are transplanted from August 1 through August 20. Garlic cloves are best planted November 1 through November 20.
Spinach for fall harvest is seeded August 10 through the end of August for fall harvest and from October 1 to October 20 for overwintering.
Lettuce for heads from direct seeding should be planted during August. Transplanted lettuce for heads best planted from August 10 to September 10. Fall adapted varieties are required. Earlier plantings may be subject to bolting and only bolt resistant varieties should be used. For baby lettuce, field plantings can continue through mid-September.
Plasticulture strawberries should be planted by September 15 for best results. Later plantings will require earlier row covering and risk lower yields.
For all late crops, variety selection is very important. For example, late planted cucurbits such as squash need broad virus resistance. For fall harvested crops, switch to shorter maturing varieties as plantings gets later. When planting late, remember that a few days delay in planting can mean several weeks later harvest. A longer maturing variety may not produce if planted too late. On the other hand, planting several maturities of varieties on the same day will often give long extended harvest in the fall for crops such as broccoli.
Protected culture using high tunnels, planting on black plastic, and using row covers will often require changes in planting dates. For example, lettuce and other leafy greens in high tunnels can be direct seeded through early November. Overwintering crops in high tunnels should be planted much later than field plantings.