On the Common Sense Homesteading Facebook page, one of the questions that comes up regularly is “How do you extend your growing season?”. I live in northeast Wisconsin, so I do use a variety of techniques to help add growing time in spring and in fall. I don't do *everything* that can be done to potentially keep food growing here year round. From my perspective, it's easier to spend time preserving some crops than battling the elements to keep them going outside. My favorites are the ones that hold “as is” with little or no effort. You can read more about these crops in “Root Cellars 101” and “Above Ground Root Cellars – Enjoy Your Local Produce Longer“.
For hardcore season extension advice, I recommend checking out Eliot Coleman's books, “Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long” and “The Winter Harvest Handbook: Year Round Vegetable Production Using Deep Organic Techniques and Unheated Greenhouses“. Keep in mind that many crops will tolerate cold weather, and some (like kale) even improve their flavor after a light frost. Spinach, mache, lettuce, radishes, potatoes, peas and onions are a few of the crops that prefer cooler (but not freezing) temperatures.
Here are several ways to extend your growing season without breaking the bank.
Start seed indoors
Figure out the average date of last frost in your area by checking with your local extension office or researching online. Then check the seed packets of your desired crops to see which ones are best started inside before setting outside as transplants. Count back from your average last frost date the appropriate number of weeks to determine your indoor planting schedule. *Note: Don’t forget to check whether your seeds need to be stratified to improve germination. Stratification is the process of placing seeds in cold storage for a time to mimic the natural freezing process.
For instance, many slow growing herbs and flowers suggest starting indoors 10-12 weeks before last frost. Tomatoes and peppers may suggest 4-8 weeks before last frost. Vine crops may be started inside 1-2 weeks before last frost (if the plants get too large they do not transplant well and are more likely to get transplant shock and be set back). You can also start seeds for fall plantings inside when it's too hot for them to germinate outside.
For more information on seed starting, see:
Create Microclimates with Dark Groundcovers and Water Filled Containers
A microclimate is a small area with a climate that differs from the surrounding area. In the case of season extension, you generally want to warm the air and soil just where you’re planting, and shelter it from excess wind and temperature fluctuations.
Watch out for frost pockets! Frost tends to settle in low lying areas. I have seen this clearly demonstrated in my garden. Our south beds are around 20 feet lower than the beds on the north side of the house. The south beds will freeze while the north beds are still intact. Of course, the north beds are more exposed to the wind until our treeline grows up, so there are pros and cons to both locations.
Raised beds will also heat up faster and stay warmer. (For those who face the opposite problem (too much heat) planting in troughs can provide cooler temps and wind protection.) An old technique was to place partially finished compost/composting manure in the center of a planting mound, and allow the heat of the working compost to warm the soil for planting. You don't normally want to plant only in working compost/rotting manure, as the heat and excess nitrogen may kill plants. Do note the raised beds also tend to dry out quicker, so make sure to plan accordingly.
Covering the ground with plastic or other dark material raises the soil temperature so you can transplant earlier. Clear plastic warms the soil well, but can promote weed growth. Black plastic mulch is commonly used, as it is cheap and blocks weed growth. I’ve been using landscape fabric for years. Recently, IRT (Infra-Red Transmitting) plastic mulch has become available, which block visible light but allows infrared light to pass through. Preheating the soil promotes better germination rates and easier transplanting.
I always use landscape fabric in my melon patches. Depending on the season, I may also do it for other heat loving crops such as cucumbers, tomatoes, summer squash, and eggplants. You may wish to preheat the soil for corn, but once it’s growing it prefers cooler roots.
Another inexpensive microclimate option is a homemade version of the well-known wall-o-water products. Fill empty plastic jugs with water, and use them to create a wall around a transplant (for instance, around a hill of melons) or at least in the direction of prevailing winds. I use gallon jugs from milk and vinegar; I’ve seen others use two liter soda bottles. These will typically last a season or two before ending up in recycling.
A good microclimate can give your garden a boost in spring and fall. In spring, it gives you an earlier start, in fall, it can buy you a few degrees to ward off light frost, especially if combined with elements like floating row covers.
Build a Cold Frame or Greenhouse
A cold frame is a box, typically with opaque walls and a clear cover. It can be simple, such as an old storm window over a rectangle of straw bales, or a custom built wooden frame and cover, or a pre-packaged unit. Most home built units are lower in the front and higher in the back to allow more sun to reach the plants, and sized to accommodate whatever used windows are available. The fronts should be at least eight inches tall so that you have room to accommodate some plant height. We have two cold frames sized to fit old patio doors. *Note: Make sure any old windows you use do not have lead paint on them. Obviously, that’s not something you want around your food.
Cold frames are unheated (except for by the sun). Their primary advantages are to protect from the wind and overnight cold temperatures. When using them (as when using a greenhouse), be careful to vent to avoid overheating on sunny days.
I have a small greenhouse attached to the southeast corner of our home. Since the greenhouse was built, I transition plants from inside, to the greenhouse, to the cold frames to out in the garden. The greenhouse has allowed me to significantly reduce the time the plants spend under grow lights. Our greenhouse is a simple wooden frame covered in multi-wall polycarbonate, and is built into the hillside as part of our retaining wall so it is earth sheltered. Many different sizes and types of greenhouses are available, depending on your space and budget. A greenhouse may or may not have supplemental heat. (Ours does not, although I can open the door to the house, and I sometimes place jugs of water in it to absorb the heat from the sun and release it at night.) I did have a mouse sneak in from the greenhouse when I left the door open, but our cats took care of it in short order.
If you'd like more information on building a greenhouse, check out 10 Free Greenhouse Plans. The video below features a greenhouse built from recycled materials.
If you need additional information on season extension, I recommend the books below.