Category Archives: Season Extension Gardens
If you’ve been reading this blog for awhile now, you know that in the past we have used “low tunnel” type row covers/cold frames. (These terms tend to get used interchangeably, although they aren’t necessarily exactly the same.)
This is what we’ve done in the past – putting either plastic or fabric over low plastic hoops to protect cool season vegetables. With the new garden, we wanted to try something new, especially something that wouldn’t be as susceptible to the wind!
We wanted to try a more traditional cold frame, which is a wooden box with a glass/plastic top. We used plexiglass. One of our Master Gardeners built this for us. (Thank you, Don!) It is designed to fit onto the red cedar raised beds, around the corner posts.
As you can see, the lid is hinged and runs on a track. It is also only about 4′ x 4′ rather than the length of the whole bed. We wanted something that would be usable but that we could still hope to lift and store somewhere during the rest of the year!
The Master Gardeners planted some spinach seeds in this raised bed the week before the cold frame was installed. They are growing pretty well, since the weather has still been warm. The day length tends to slow the growth down at this time of year as well. You can see we still have the lid open, since it hasn’t been getting consistently cold. I might see about closing it for today and tomorrow, then opening it again later in the week.
Overwintering Vegetables for Spring
There are two groups of vegetables that can be successfully overwintered into the spring: root vegetables and very cold hardy leafy greens.
Root vegetables should be planted early enough that they are a mature size for harvest by mid-November. As the ground begins to freeze, the root vegetables can be heavily mulched with straw to keep the soil from freezing. This method can provide an outdoor cold storage for the root vegetables. They can then be dug and used throughout the winter, as long as the soil is not frozen. Row covers can also assist with this goal.
Spinach, kale, some varieties of lettuce, and some specialty greens such as mache and claytonia are very cold tolerant and can be successfully overwintered with a couple layers of row cover. Depending on the winter and the amount of protection given, these vegetables may be harvestable for much of the winter or they may not have harvestable leaves until it is warmer with longer days in early March.
Kansas Climate Conditions for Winter Gardens
While most gardeners consider temperature to be the limiting factor in growing vegetables during the winter in Kansas, often it is the amount of sunlight that truly limits plant growth, because row covers and other techniques can keep very cold hardy plants alive throughout the coldest part of the winter.
From November 20th to January 20th there is less than 10 hours of daylight in south central Kansas. Most fall planted vegetables will exhibit extremely slow growth during this time period because there is not enough sunlight to encourage more growth. Any vegetables still alive during this timeframe should be either harvested and enjoyed or protected for growth to resume in the early spring. If you are planning to overwinter any vegetables or keep them past mid-November, you should plant early enough that they are mostly mature by mid-November.
In south central Kansas, our average low temperatures throughout the winter months show that we can successfully sustain many of our cool season vegetables throughout the winter.
Average Winter Months Low Temperatures:
November – 34 degrees
December – 24 degrees
January – 20 degrees
February – 25 degrees
March – 34 degrees
Although we can have winter low temperatures down below zero, many vegetables will be able to tolerate those short-term low temperatures if given adequate protection with row covers and mulch.
While heat is the biggest challenge when planting your fall garden, by the end of fall there is the challenge of cold weather. In an average year, the first light frost will usually occur in mid- to late October, although sometimes the first frost occurs sometime in November. A light frost, where the low temperature dips down to 30-32 degrees will not damage fall vegetables. The cold may even improve the color and flavor of the vegetables. Most fall vegetables will tolerate temperatures down to 28 degrees without significant damage. In fact, allowing exposure to below-freezing temperatures will often allow the plants to better adapt to the cold, increasing their hardiness to later cold weather.
On a cold morning before the temperature is back above freezing, your plants may look wilted and permanently damaged. However, by the time the temperature is back above 32 degrees, they will recover and continue growing. It is important not to harvest these fall vegetables until the temperatures are back above 32 degrees and the plants have naturally recovered from the frost.
When low temperatures dip below the mid-to upper 20s, it will be necessary to protect semi-hardy fall vegetables with a light row cover to minimize damage on those vegetables. Some particularly hardy vegetables, such as spinach and kale, will not need extra protection until the low temperature is near 20 degrees.
It is usually best to remove the row covers during the day to allow the sun to warm the soil more efficiently when we are still getting intermittent frosts. As we get later into the year, leaving the row covers on may help create a mini “greenhouse effect” and prolong your growing season once we are regularly dipping into the 20s overnight.
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.