EXTENDING THE GROWING SEASON – Part 2
Using Season-Extending Structures to Get Weeks, Maybe Months, of More Veggies. Plus More Strategies and Thoughts.
I get it. It’s been a long summer of “enjoying” the garden and you’re exhausted. Or you live in the far north and it’s too much work to get a garden going beyond September. Or, for whatever other reason, you’d rather just let the garden sit, covered in a mounding mulch of dead tomato plants (or sheets of cardboard?!). Yes, there are plenty of good reasons to not encourage your vegetable garden to go further into fall or, heaven forbid, into winter. [An acknowledgement, of course, to gardeners in the deep south, the Southwest, most of California, and the west side of the PNW — gardening in the fall and winter there is just a thing you do because summer is for vacation.]
For the rest of us, fall and winter are prime seasons for keeping the edibles action going and, in many cases, a time to cover or otherwise protect veggies from the cold, hail, sleet, heavy rain, snow, and other weather sh*t that can be expected to beat up a garden, sometimes catastrophically.
Last week, I wrote about some basics — planning, timing, microclimates, succession sowing, filling in the gaps — along with various other principles, techniques, and tips of how to keep the planting, growing, and harvesting going. For many of us, all of that is a good start and a way of getting the garden going for at least a productive short time. But for almost all of us, there comes a time to protect the garden goodies from the serious bits of weather. Hence this part about season-extending structures.
There are several of these structures that can protect plants from cold weather and extend their growing season beyond that cold. Certain structures and materials allow gardeners to continue growing vegetables well past (or before) the frost/freeze dates. Maybe up to 6 weeks more. Examples of season extenders include:
Cloches: A small cover, of mesh, solid cloth, or transparent material, to cover individual plants or just a few plants.
Cold frames: Enclosed structures with a transparent top that trap solar energy and create a warmer microclimate.
Hot beds: Take a cold frame and add bottom heat, either “naturally” (in the old days, it was a bottom layer of fresh manure) or with an electric bottom heat system.
Row covers: Lightweight fabric that allows light and water to pass through, protecting plants from wind and lightest frosts.
Low tunnels: A temporary, hoop-supported structure, often covered with spun-bond fabric or polyethylene film, usually in the 2- to 4-foot high range.
Hoop houses: A fairly simple, unheated covered structure made with flexible hoops of pipe, usually PVC but can be steel ($$) and covered with a polyethylene plastic; built at a height to walk through. Essentially a greenhouse with no heating equipment. Sometimes called a “high tunnel.”
Greenhouses: A permanent building (or at least until it falls down) with a rigid framing, covered in glass or, just as commonly, polyethylene (PE) and/or polycarbonate. It’s heated by passive solar heating, at the least, or, better, an active heating system, and, in an old-technology way, composting.
They all work in similar ways by maintaining a higher temperature during the day and protecting plants from wind and moderately low to very low temperatures at night. Your choice will depend on quantity of plants, size/height of plants, expected winter temperatures, other environmental stresses, and the amount of money in your bank account.
CLOCHES
Also called “hot caps,” are kind of like mini greenhouses. They’ve been around for centuries to protect plants from extreme cold as well as extreme heat. The earliest, officially known forms were bell-shaped glass (Italian, of course) jars from the 17th-century. No doubt solid clay covers were used long before that. The term "cloche" comes from the French for bell or a woman's close-fitting hat. Being heavy glass, they were expensive but those without money improvised in many ways, including using easily made clay covers, such as those from way back.
Nowadays, they’re made of various plastics in various permutations on the bell form. They come in sizes, from little bells to fit over the newest of seedlings, to much larger multi-plant coverings to fit over a short row of plants, yet still lightweight and movable.
In addition to the specialized cloches you can buy, and there are many, they can be made from everyday items around the house. You can cut the bottom off the many various plastic bottles of so many sizes, keeping the cap to put on during the night to keep the heat in and take off during the hottest days to keep the plants from cooking. Almost anything else of the appropriate size and material will do in a pinch, as long as you can ventilate them or remove them, depending on the material and the day temperatures.
Because this type of cover won’t be on the plants for more than a day or two early in the season, it doesn’t need to be translucent. For longer protection, though, it does need to be made of a transparent material, such as glass or clear plastic, to allow good light transmission.
[In addition to its primary use of shielding crops for one or two days from imminent frost or worse, transparent cloches can be used as tiny greenhouses for a few six weeks to kick early-planted or tender crops into gear.]
Make sure you remove or vent cloches when temperatures exceed 40°F to protect plants from overheating. Because common fall vegetables do not bloom and do not need pollinators, there is no need to uncover them for the bees and such (the native pollinators have probably all gone into rest mode in the fall.)
COLD FRAMES
Simply put, a cold frame is a raised box, very much like a familiar raised bed, with a transparent lid. It’s a wonderfully simple and more permanent solution for extending the growing season. Think of them as little greenhouses built close to the ground. As with greenhouses, both cold frames (and hot beds, next) heat up as the sun throws its energy through the clear cover and the cover then traps that energy inside.
You can make your own cold frame (and hot beds) or you can buy a kit ($) or even a pre-built model ($$$). The framing material is almost always made of wood but I suppose resourcefulness and creativity can play a big role in this. The lid/covering may be made of glass (e.g. old windows), plastic (preferably greenhouse sheeting), polycarbonate (not fiberglass), or similar, transparent materials.
Most gardeners I know, build their cold frames in the same manner they build their raised beds – from salvaged materials. It’s about old windows and scrap lumber. The frame is built to fit the window (or windows).
A cold frame is most commonly built with it’s back wall higher than the front wall and the side walls cut at an angle. This allows the cover to lay at an angle that maximizes sun exposure and allows rain and snow to run off easily. Hinges hold the cover in place.
Or, for easiest construction, instead of cutting two pieces into different heights and two sides on a slant, you can build the frame as a box, simply top it with the storm window, and skip the hinges. When it’s hot, slide the window to the side to let heat out, and on cold nights, put the window back on top. There’s a risk of not getting the top on tightly with this design, though, so you might consider this only where your fall and winters aren’t deadly cold.
The ideal location for a cold frame is facing south and on a slight slope; that further helps with cold air and water drainage plus it makes more use of the sun in the south. You can also situate it with its back up against a wall for additional heat and protection against cold winds.
The cover needs to be pulled up or off when daytime temperatures go above 50°F and put back down or on when temperatures drop below 45°F. If you don’t already have some kind of apparatus built in to firmly hold the cover up, use a block of wood, a brick, a shovel, or whatever. With a little extra cash, you can pop for a solar-powered vent opener that automatically opens and closes the lid as temperatures dictate.
If you take vegetables through winter in your cold frame, you may have to keep it closed all winter (depending on where you live, of course), but don’t rule out those unseasonably sunny, warm days. Keep a thermometer in the cold frame to help monitor temperatures. In the really snowy zones, don’t forget to brush off the covering after each snowfall.
The hardiest vegetables can be transplanted to, or grown in pots in, a cold frame to overwinter. That especially includes small greens for salads throughout much of the winter (in all but the coldest climates). You can help protect them by stuffing straw around the base of the plants or pots to insulate the roots against freezing temperatures. Soil piled around the outside of the frame provides added insulation and heat retention.
You can also design a cold frame to be deconstructed, making it easy to disassemble for the summer, when you won’t be using it, to store until fall, should you want to or need to.
Besides their fall-winter application, cold frames are also the best way and place to start certain seeds in winter or earliest spring. Those certain seeds can be the types that require a time of stratification (winter chill) or the hardy seeds that you want to get started early regardless of chill needs. The beds may further be used in the spring to start harden off maturing seedlings. Yes, I love cold frames and I might write a detailed piece on them in the future. Or maybe not; Gretchen at Backyard Farming did an absolutely super piece on cold frames not long ago:
HOT BEDS
Hot beds are built pretty much the same way and with the same materials as cold frames. But there is a difference: while a cold frame uses only sunlight to maintain an appropriate core temperature, the hot bed uses either an electric heat mat or another outside heat source to regulate the temperature more uniformly and precisely. Hence why hot beds are sometimes called “heated cold frames.”
Methods for heating the beds include electric cables or mats and even, in a pinch, manure. The heating element is built or placed at the bottom of the frame, of course, and usually in a bed dug deeper than where the frame would rest. It’s laid upon loose, level sand (or light soil).
A thermostat is necessary to maintain uniform temperatures. Some cables/mats have built-in thermostats that can keep the soil temperature close to 74°F or be adjusted to any temperature.
An old-fashioned method is the use of manure as the heat source. This is for temporary hotbeds, which can be made by simply placing the frames on top of a deep, flat pile of manure, with additional manure banked against the sides of the frame for insulation and heat retention. Manure heating is suitable for short periods only, whether in fall or spring.
Although light bulbs are less expensive, they are also less satisfactory as a heat source. But they can be used to provide a quick and easy means of adding supplementary heat on frosty nights in early fall and/or to add day-length during the shortest days of fall-winter.
ROW COVERS
Row covers, or “floating row covers,” are gauzy, reusable (if treated with care) spun-bonded or woven plastic materials (polyester or polypropylene) that are used during the spring and summer growing seasons to keep off pests such as insects, birds, and deer, and during the fall into winter season to insulate newly seeded or transplanted veggies early on from light frosts and cold weather and larger growing plants from serious freezes and heavy snowfall.
They are meant to sit on top of hoops or directly on the plants to provide a few degrees of frost protection. On sunny days, they trap warmth by creating a mini greenhouse effect. Heavyweight covers, called "“frost covers,” “thermal fabric,” “frost fabric,” “winter cover,” and “frost protectors,” on mini hoops, sometimes combined with an added layer of greenhouse plastic, will safeguard many edibles into winter.
These frost covers trap the heat rising from the soil at night. The point of covering plants is to trap the earth’s heat, not the plant’s heat. Commercial frost covers have several advantages over home-improvised coverings (e.g., sheets and blankets): they allow light through during the day they allow moisture to escape, and they prevent the freezing air from coming into direct contact with any moisture on the plant. If used for too long a time, though, they can prevent the crop from developing as much hardiness as an uncovered crop, due to the artificial mild climate under the cover. Frost covers are most effective when the sides are pinned down to the ground.
If you do not plan on using hoops, leave enough slack when covering rows so the cover can inflate as the crop grows.
Hoops or not, covering should be secured, even crudely, to prevent them from blowing away. This is especially crucial in exposed locations.
Mediumweight row cover can raise the area temp by 2 to 5 degrees while those labeled as “frost covers” are sold in medium, heavy, and extra heavy with the heaviest grade of course providing the best frost/cold protection. Heavyweight row covers, although offering more insulation, allow less light to pass through. If placed over young, actively growing plants too early in the season heavyweight material can delay, stunt, or damage the crops.
Row covers used from spring through summer and maybe into fall, usually to prevent pest damage, are “light weight.” They’re not meant for cold protection.
Frost cover protection of any kind (except those needed for shading) needs to be removed each morning as soon as temperatures begin to warm. With direct sun on warm days, temperatures under frost covers build quickly, resulting in heat damage to new growth. Air humidity would be higher under the cover during the day, too, and this would increase the occurrence of certain plant diseases.
Row covers are generally removed at the end of the season, rolled up, and then stored.
LOW TUNNELS
These structures are essentially larger, longer structured row covers created, in their simplest fashion, by using hoops of EMT conduit* to support a heavier material such as frost cloth, usually, or sometimes plastic (sometimes both, for added protection). They provide a warmer and more stable environment than a row cover simply laid on top of the plants.
[* PVC piping, although almost ubiquitous for use here, reacts with plastic covers (including most row cover materials), causing the plastic covering to age rapidly and tear in a couple of years.]
Whatever is used for covering, the cover must reach the ground completely — at the sides AND ends — to trap the warm air inside the canopy. The edges of the covering can be buried a few inches with soil.
The curved hoops should reach about 1 ½ to 2 feet each way from the center of the row, with the ends secured in the soil. Hoops can either be pushed into the soil or, easier, they can fit over rebar that has been driven into the ground. If a raised bed is to be covered, PVC piping with an inside diameter oh-so-slightly wider than the outside diameter of the EMT conduit, can be attached to inside each corner of the bed; the hoops can be easily removed and re-inserted anytime.
Low tunnels should be opened at their ends when outside temperatures rise above 40°F. If considerably warmer than that, start lifting the sides. Grown too warm, cool-season vegetables tend to grow soft and are more susceptible to diseases and cold damage. Close the ends (and sides) back up before nightfall. If using plastic on a low tunnel, be careful to not allow the covering to touch the vegetable foliage. As with all coverings, brush snow off the covering as soon after a storms you can. Also, monitor soil moisture; plants under such tunnels don’t get rainfall. You probably should install a tunnel system with its own dedicated irrigation system.
After the season, take down the low tunnels, clean the pieces well, patch any holes, and store them until next season. In worst cases, replace the covering and/or the support pieces.
HOOP HOUSES (POLY-TUNNELS)
A hoop house is a more permanent season extender that acts similarly to a greenhouse in that you can walk inside it. The heat retention in a hoop house is almost equal to a good greenhouse and, with proper ventilation and care, a hoop house can extend the growing season by months (depending on your Zone, of course). Hoops are set four to six feet apart, depending on expected wind and snowfall.
The most effective and efficient way is to build one over two existing 3- or 4-foot wide raised beds, each 8 feet or more long, with a wide walkway in-between and narrower walkways on their outsides. It should be tall enough to walk into and wide enough for multiple rows of vegetables. Keep in mind, though, that bigger isn’t always better — the larger the structure, the harder it is to keep warm.
Ideally, cover the hoops with UV-resistant 4- to 6-mil polyethylene. As with low tunnels, the poly should contact the ground on each side of the hoop along the entire length where they should be weighed down. At the ends, leave an extra six feet to gather up and secure to a sturdy stake. Hold it all in place with ropes, pulled taut over the tunnel and fastened to posts at both ends. Of, if you’re handy with wood, hammer, screws, and such, build a door at one end (as pictured above).
GREENHOUSES
The most effective solution for extending the growing season is undoubtedly a greenhouse. But yes, it’s the most expensive. Does it pay for itself with more produce? I haven’t seen the numbers but a greenhouse is certainly useful for a lot of things, not just extending the fall vegetable season.
Even without the usual accoutrement ($$$), the passive heating in a greenhouse can prolong vegetable growing and harvest, for maybe another two months beyond a serious frost. The construction doesn’t have to be costly or complicated, either. Many (most?) I’ve seen were built from whatever wood, glass, and/or metal, could be scavenged, scrounged, and traded for. Although I always recommend a minimum size of 15 feet by 20 feet (for the most effective, efficient use over the long haul), smaller greenhouses can be built for nothing more than keeping a couple beds worth of veggies going into winter.
Clear greenhouse plastic, the same as I recommended for hoop houses, is the most effective and most commonly used covering. Sometimes two layers are used and air is pumped between the layers, via a low-cost “squirrel fan,” to provide more effective insulation. Do not use painter’s plastic nor any other thin, transparent plastic. The plastic should not be allowed to touch the plants; plastic that touches the plants can often be even worse than no protection since it can hold moisture against plant tissues and cause more serious freeze damage.
You can, of course, buy greenhouses, usually as kits (although the small, really cheap “ready-to-go” models are rarely worth the price). Whatever you buy, make sure they can withstand your winds and rain.
With more money (+$ to +$$$), you can add all manner of toys (climate control systems and more) to take your greenhouse all the way through the year, from fall to fall. The more useful:
Ventilation — critical in hot and/or humid climates. Automated systems open up the vents when the temperature reaches a set point.
Heating — critical for cold fall and winter climates or for growing tropical vegetables (sweet potatoes, anyone?).
Heat mats — for getting seeds going.
Shading, shade cloths — for growing through summer or even during winter where the sun shines a lot.
Monitoring temperature — starting with simple thermometers to min/max thermometers to computerized systems that can be connected to your phone and/or computer(s).
Watering system — you will have to water your plants. You can run piping to the greenhouse to then install a specialized system. You can automate it with simple timers or computerize it in so many ways. There are even monitoring systems that can tell you when to water based on plant needs or tell you when to water based on weather forecast apps on your computer.
Light — supplemental lighting helps significantly, especially during short winter days.
Shelving and benches — You can certainly grow vegetables in the ground in a greenhouse but for maximizing your growing space, especially in smaller greenhouses, shelves, benches, and even tables are a must.
Power source — yeah, if you do go with a lot of the stuff mentioned above, you have to figure this one out. I’m keen on using solar and wind energies to charge storage batteries that can be used to run greenhouse systems and even used for charging battery-powered garden tools. No expensive, elaborate wiring system to the house needed.
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ADDITIONAL NOT-EXACTLY-STRUCTURAL STRATGIES FOR GETTING THROUGH THE COLD
Mulching
Mulching root crops will help extended their harvest season into cold winter areas. That is, it will keep the ground from freezing solid and harvesting will be easier.
But mulching with organic matter, probably has little, if any, impact on frost or frost protection. Mulches will certainly insulate the ground, preventing temperature swings, and it will allow less heat out at night but common mulches allow less heat to be absorbed by the soil during the day countering the nighttime heat loss.
Dark, inorganic mulches, such as black stones or gravel, on the other hand, raise soil temps early on, retain heat during the day, and release it slowly during the night in the manner of thermal mass for passive solar radiating, thereby “pushing back” against a downward frost. Such mulches also maintain warmth longer into the season. Stones and gravel allow rain and oxygen to penetrate into the soil; black plastic does not so don’t use it.
Watering the ground
Added soil moisture has the beneficial effects of increasing the capacity of the soil to store heat and improving conduction of heat to the surface. Watering plants during late summer and autumn prevents them from entering the winter under drought stress. Dry soils predispose plants to winter injury and cankers.
On the other hand, a wet soil gains heat more slowly during the day and the increased evaporation uses up heat energy. Another reason to water in the earliest hours of the morning.
Don’t overdo the watering just before a hard frost/freeze. Foliage inflated with excess water is more prone to bursting after a frost, which is the resultant cause of the dying, wilting when the sun comes up the next day.
Overhead sprinkling
Putting water onto the tops of plants when serious frosts/freezes are expected is a common practice in commercial orchards. It’s primarily used for marginally hardy plants, especially broadleaved evergreens and provides a two- to five-degree temperature difference, which is just enough to protect most plants under most expected conditions and has been shown to protect plants down to as low as 20°F. It works because the ice that freezes from the added water encases the plant’s foliage and partially insulates it from the harsh exterior temperatures. So when the temperature outside is 28°F, the temperature inside the ice is 32°F (the temperature of frozen water).
Sprinkling should begin immediately before the onset of freezing conditions when the immediate surrounding temperature is about 31° or 32°F or, if temps seem to be dropping quickly, at 33° or 34°F. Apply the slightest film of water (no more than 1 gallon per minute over 1000 square feet). The sprinkler water will start to form ice at 32°F, of course. Run the sprinkler continuously but stop irrigating when the ice begins to melt as temperatures rise above freezing(32°F).
If you do want to look into this kind of frost/freeze, look for wobbling sprinkler heads; the head of this type, instead of being rotated in a smooth rotation, has a distribution head that wobbles in a rotating fashion to provide a more even distribution of water. Familiar sprinkler heads aren’t very effective/efficient for doing this.
Stop fertilizing
Especially avoid nitrogen fertilizers late in the season. Fertilizers of almost any kind will produce overly soft growth, easily damaged by frost/freeze.
Move Containers Indoors or to Sheltered Areas
If you’re growing vegetables in containers, move them to or near a south-facing wall, inside the covered porch or patio, or simply into the garage for the night. Move them back out into the sunny spot as soon as temps rise about 35°F-ish. And there’s always frost cloth (not blankets, and definitely not plastic sheeting) in a pinch.
My favorite way: Watch/listen to weather news regularly
Be prepared. It’s too easy to check the weather app on your phone. I do every day of the year, not just for fall frosts. Keep the row covers, hoops, greenhouse plastics at the ready. The preceding methods to help you get through the cold and sh*t are presented as ways to proactively get ahead of weather that may or may not be coming. Even if you don’t actually put these methods into practice in advance, you should keep them in mind should the weather change.
Finally: Take Notes for Next Season.
Write down what worked and what didn’t. Write down dates, places. Use the notes to fine-tune your vegetable types and varieties, your timing, and your strategies for the next year.
As with all of gardening, growing vegetables into the weather-extreme party of the year is as much about learning as it is about the growing. If you’re going to do this, you might as well do it the best you can. [Is that a song or a quote?]
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Getting vegetables through winter is almost always a combination of plant selection as well as several growing and protection strategies. There’s rarely one silver bullet.
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JUST IN CASE…
For those of you who are exhausted or not interested or …? … and a vegetable garden through fall (and winter) is not on your schedule but you do have a designated plot (especially raised beds), there is something you should do.
The most important thing is to cover the ground. To protect and encourage the soil life, to help retain and/or build structure, and, should you live where the ground actually freezes, to minimize heaving.
The best way to do that is to sow a cover crop. Visit your favorite on-line seed company or your local farm-and-feed store to find out which species or combination of species is right for your area and your needs. Sow it late summer or earliest fall. Let it grow, let it die (if that’s what it’s meant to do) in winter and then leave it, or let it grow into spring and then chop it down before planting your next spring crop(s). Do NOT “dig/till it in.”
At the minimum, if you do not want to invest time in cover cropping (although it really doesn’t take that much time overall), put down a thick mulch of coarse, partially composted organic matter.
Come spring, you will be on your way to your best vaggie garden ever.
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“Among famous traitors of history, one might mention the weather.” ~~ Ilka Chase (actress, radio host, novelist)
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© Copyright Joe Seals, 2025