While tomatoes and peppers thrive in the summer heat, many crops prefer the cooler weather of fall. Cool season crops, such as broccoli, cauliflower, and lettuce, may bolt (go to seed) or become bitter in summer making them prime candidates for fall gardening. Planning for a fall vegetable garden is a great way to make up for spring mishaps or just extend your garden harvest. To get started you'll need seeds and a calendar.
It's All About Timing
Timing is everything in fall gardening. If started too late, vegetables will not have adequate time to produce a crop before being damaged by a hard frost. If started too early, the summer heat can inhibit the growth of cool season crops. Several factors determine correct planting dates. The amount of time needed from planting to harvest is the major consideration. Gardeners should also allow time for the harvest. Tender crops that are quick to maturity will require additional time since they will not tolerate a light frost. This additional time allows for slower growth in cool weather and ensures a harvest in the event of an early frost. Once you have the total time needed to produce a crop, work backward from the average first frost to find the sowing date. In Iowa, the first frost arrives between September 30th and October 15th.
What to Plant
Vegetables can be classified into three groups based on their cold tolerance. Tender crops will be damaged or destroyed by a light frost, semi-hardy crops can tolerate temperatures in the upper 20s oF, and hardy crops will survive temperatures in the mid to low 20s oF. When possible, purchase varieties that are short-season or "early" to minimize the time period from planting to harvest. Seed will need to be purchased early before it is removed from stores.
Some choices for fall vegetables in Iowa include:
Tender (Not frost tolerant, but relatively quick to maturity)
- Green beans
- Summer squash, such as zucchini
Semi-Hardy (Tolerate temperatures down to the upper 20soF)
- Swiss Chard
Hardy (Tolerate temperatures down to the mid to lower 20soF)
- Brussels sprout
High soil temperatures can inhibit seed germination on some species. The application of a light mulch will help cool the soil and aid in germination. When planting seeds in summer, the soil surface should be roughed up to aid in seedling breakthrough. Some gardeners may pre-sprout seeds indoors between moist paper towels before planting in the garden, taking care not to damage the tiny plants. Seeds may need to be watered periodically for proper germination.
Other plants that are longer to maturity, such as broccoli, cauliflower, or Brussels sprouts, benefit from being started indoors and transplanted in the garden. For many of these crops, seed can be sown indoors six to eight weeks before the fall planting date and transplanted outside in mid to late August.
The harvest period for tender and semi-hardy plants can be extended by protecting the plants from cold temperatures. Blankets or sheets can be placed over the crop with proper support to avoid physical damage. Milk jugs or floating row covers can also be used. Remove the protection as soon as the temperature rises above 32oF. In a cold frame, certain crops (such as lettuce) can be grown well into the winter months.