Fall Gardening: Dealing with Late Summer Heat
Okay, I know this is a little bit after the fact, but now you know, right?
Dealing with Late Summer Heat
When establishing vegetables during late summer heat, there are several techniques that can make your plantings more successful. Using shade cloth, mulches, transplanting, and careful watering will all improve your fall garden success.
A white or black, lightweight shade cloth can be used either close to the soil surface to help with seed germination or 1-2 feet above the ground to provide light shade to seedlings and transplants. The shade cloth will help cool the soil and the air temperature around the plants, as well as reduce moisture loss from the soil. A shade cloth that is too thick or heavy will reduce the light penetration too much and can reduce air flow, resulting in poor germination or plant growth. The shade cloth should be removed either after seedlings or transplants are well established or when the temperatures become more moderate.
Mulches of organic materials (straw, shredded paper, wood chips, herbicide-free grass clippings) have the effect of cooling the soil. They will also help keep the soil more evenly moist when germinating seeds. These mulches can be applied very close to the seeding row or around new transplants. It can be very effective to apply the mulch to an area up to 2 weeks before planting, allowing the soil underneath to cool slightly. Then the mulch can be pulled back for seeding or transplanting later.
Later in the fall, mulches can be removed to allow better warming of the soil by the sun to encourage late fall growth.
Some fall garden vegetables must be planted by transplants to provide a long enough growing season. Broccoli, cauliflower, cabbage, onions, leeks, and radicchio will all do best if seeds are started indoors 4-6 weeks before transplanting. Onions, leeks, and radicchio are often very slow to grow from seed and may need to be started even earlier. Root vegetables (beets, carrots, radishes, and turnips) do not generally transplant well.
Starting leafy greens and similar vegetables indoors allows them to get a good start when the weather may still be too hot outdoors. For example, lettuce started in late July will be ready to transplant into the garden by late August, giving you a 4 week head start on your fall lettuce crop. You can then seed additional plantings directly in the garden if desired.
When transplanting vegetables in the late summer, it is important to give the plants a chance to adapt to the warm and windy outdoor conditions. Plants should be set outside for 1-2 weeks to adapt to the brighter light and higher temperatures. The first day, place the plants in a protected location with partial shade for only a few hours. Each day for 7-10 days, they should be placed in a location with more exposure to the sun and other elements. During this time they should receive adequate water, but not excessive water so they can adapt to drier conditions.
Managing Water Needs
When direct seeding in the garden in late summer, it is important to keep the top 1-2 inches of the soil evenly moist to facilitate seed germination. Typically the seeds will germinate quickly due to the warm soils, and then you will need to gradually reduce watering to encourage deep root growth.
Likewise, newly planted transplants may need more water initially, but you should decrease watering quickly to encourage deep root growth.
As the weather cools and we experience more frequent fall rains, less water will need to be applied. In some falls, there will be adequate rainfall for a successful garden. Most fall gardens will need about 1 inch of water each week after the heat of the summer has passed.