Emmalea Ernest, Extension Fruit & Vegetable Specialist; emmalea@udel.edu
Plantings for some fall harvested vegetables have started and others will be underway soon. Timing these plantings can be a challenge, especially where a continuous supply of fresh product is desired. This article summarizes strategies for achieving a continuous harvest of vegetable and the planting window for each crop.
Mid and late summer vegetable plantings can be divided into 2 groups: 1) warm season vegetables for harvest up to a killing frost and 2) cool season vegetables for extended harvest in the fall.
Warm season vegetables for fall harvest include snap beans, squash, and cucumbers. July plantings of sweet corn can extend seasons for farm stands. Mid-July plantings of tomatoes and peppers can be made for late harvests, particularly in high tunnels.
Cool season vegetables for fall harvest include cabbage, broccoli, cauliflower, kale, collards, mustard and turnip greens, turnips for roots, spinach, beets, lettuce, leeks, green onions, and radishes.
The three main factors influencing crop growth and performance in the fall are daylength, heat units, and frost or freeze events. Because of lower temperature and shortening daylength later in the growing season, a few days difference in planting date in the summer can make a big difference in days to maturity in the fall.
For some crops, an extended harvest can be achieved with successive plantings. Planting cutoff dates depend on the crop, variety, and whether season extension methods like row covers or high tunnels will be used. When using succession planting in late summer, the number of days between plantings will need to be compressed; a one day difference in planting in early August planting can result in a harvest date difference of several days.
Another strategy to extend harvest in the fall is to plant several varieties with different days to maturity at the same time. This is particularly successful with crops such as broccoli, cauliflower and cabbage where maturity differences of more than 30 days can be found between varieties.
Row covers, low tunnels and high tunnels can be used to protect crops from freezes and extend the harvest season further. These methods also allow for more heat accumulation and faster growth during the fall. Decisions on what type or combination of covers/protection to use and when to apply the protection will influence fall vegetable maturation and duration of harvest. In general, plantings of cool season crops can be made 30-45 days later in high tunnels than in outside production.
Below are the recommended planting windows for fall vegetable production in Delaware.
Planting Window for Fall Harvested Warm Season Vegetables
Cucumbers: Direct seed July 10 through August 7 (high tunnel transplanted up to September 1)
Lima Beans: Direct seed June 15 through July 20
Peppers: Transplant up to July 10 (high tunnel up to July 30)
Pumpkins and Winter Squash: Direct seed through June 30
Snap Beans: Direct seed July 10 through August 10
Summer Squash: Direct seed July 15 through August 15 (high tunnel up to September 1)
Sweet Corn: Direct seed July 1 through July 31
Tomatoes: Transplant June 20 through July 5 (high tunnel up to July 30)
Planting Window for Fall Harvested Cool Season Vegetables
For transplants, seed 3-6 weeks prior to desired planting date (8 weeks for leeks and onions).
Beets: Direct seed July 1 through August 10
Broccoli: Transplant July 15 – August 20
Brussels Sprouts: Transplant June 20-July 10
Cabbage: Transplant July 1 – August 10
Carrots: Direct seed June 20 through July 5 (high tunnel up to August 1)
Cauliflower: Transplant July 20 through August 10 (see Cauliflower Varieties for Fall Production for variety recommendations)
Collards: Direct seed July 15 through August 15
Turnip Greens: Direct seed August 1 through September 10 (high tunnel up to September 30)
Turnip Roots: Direct seed through August 20 (high tunnel up to September 20)
Kale: Transplant July 15 through August 30
Direct seed July 1 through August 15 (high tunnel up to September 30)
Leeks: Transplant July 20 through August 10
Lettuce (head): Transplant August 10 through August 30
Direct seed August 1 through August 20
Lettuce (baby and salad mix): Direct seed August 1 through September 15 (high tunnel up to October 15)
Mustard Greens: Direct seed August 1 through September 10 (high tunnel up to September 30)
Onion (green bunching): Direct seed July 1 through August 30 (high tunnel through September 30)
Parsley: Direct seed July 15 through August 15 (high tunnel through September 15)
Pumpkins and Winter Squash: Direct seed through June 30
Radishes (salad): Direct seed August 1 through September 30 (high tunnel through November 30)
Radishes (Daikon): Direct seed August 1 through September 10 (high tunnel up to September 30)
Spinach: Direct seed August 10 through August 31 (high tunnel up to September 30)
Swiss Chard: Direct seed July 15 through August 20 (high tunnel up to September 30)