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10 Tips for Protecting Cool Season Vegetables

2019

updated 3/1/2024

Here are 10 Tips for protecting cool season vegetables from freezing temperatures.

Cool season vegetables: from the top, broccoli, leeks, ‘Red Russian’ kale, light green mustard greens, and collards.

Ready For Fall?

Throughout parts of the United States, and in chilly climates everywhere, gardeners are scrambling to save their tender plants. Most of us have brought in all the houseplants. More laissez-faire gardeners do nothing special to extend the season, beyond harvesting the last of the cherry tomatoes and clearing out the frosted vines.

And there are those of us who strive to keep cool season vegetables growing even in winter. And we’ll plant more of them! Soon I’ll transplant ‘Monstrueux de Viroflay’ spinach seedlings into pots, to grow on the deck through the winter. This French heirloom spinach has huge leaves with a milder flavor. It has lower levels of oxalates, so those who have been advised to avoid eating spinach might be able to eat this variety. Ask your doctor.

In early October, I planted 2 dozen onion sets (for green onions) in a 12″ pot on the deck. Green onions are ready for harvest, in mild weather, only a few weeks after planting the sets. To preserve them in the cold, I’ll cover them with plastic sheeting (Tip #2). Green and bunching onions grow more slowly in cold weather.

I planted more sets every couple of weeks and will soon plant the remaining bulbs before they dry up. A favorite bunching onion called ‘Nabechan’ has straight sides. Not having a bulb at the bottom makes it easier to harvest. Sets are not available for bunching onions, though, so they must be started from seeds.

Where There’s a Will, There’s a Way

The USDA plant hardiness zone map.

Potted cool season vegetables will grow under a plastic covering in cold weather. To extend the season, strings of miniature incandescent Christmas lights (Tip #6) will raise the temperature to more comfortable levels. Later in this article, I will list all 10 Tips for protecting crops in winter.

Starting with the simplest ideas and progressing to the more advanced methods, find the level you’re most comfortable with this season. Your budget, your USDA plant hardiness zone (photo, above), and the types of crops themselves must factor into your decision.

As you gain confidence and become more motivated to keep the garden producing, you might decide to try the next level. Cost savings realized by growing your own fresh food might justify the expense of new materials.

It’s only through experimentation, by taking a chance, that you might discover all the opportunities—and the limits—of gardening challenges. This is how green thumbs are cultivated.

If you’ve never grown cool season vegetables, several articles at The Farm In My Yard provide detailed information to get you started. For a greater understanding of any issue, enter the term in the search bar or click it in the tag cloud.

The Advantage of This Latitude

I’ve been growing greens in winter for decades, for my customers and for my family. Fortunately for us, living in the southeast doesn’t present as difficult a winter hardship as would living in Montreal, Montana, or Scotland. But there are options for just about every climate.

There’s no substitute for stepping outside and collecting a green onion, a mild mustard leaf, and some kale and spinach for our Sunday morning omelet. We pick what we need when we need it.

Succession Planting: Warm, Then Cool Season Vegetables

Because our favorite greens love cool weather, they grow in the garden after the tomatoes, peppers, and cucumbers have been harvested. So, with some planning, you can schedule a succession of crops. When one crop finishes up, new transplants or seeds are ready to take its place. Now, that’s an efficient use of space!

Cool season vegetables and greens replace summer tomatoes and peppers. Plastic protects plants on very cold nights and the netting deters deer.

Radishes, beets, spinach, and other fast-growing plants can be sown directly into the garden in late summer to early autumn. After they’ve been harvested, there might be time for another quick fall crop.

Certain greens and root vegetables have a shorter window of time during which they retain the best quality. So don’t let them linger in the garden. On the other hand, some cool season vegetables can be harvested over many months of growing! That’s at a time when there are fewer weeds, fewer bugs, and less drought to worry about.

If the weather is still warm for the first round of seeds, look for varieties of cool season vegetables that are more heat tolerant. Some catalogs indicate the preferred soil temperature for each crop, or you can get that information from your agricultural extension office. Soil temperature can be lowered by irrigating during hot weather. Additionally, frames covered with knitted shade cloth, made from black polyethylene (available from Johnny’s Selected Seeds and others), provide consistent shade until the weather cools. That bit of shade can make the difference between seeds germinating in August or having to wait until late September to sow them.

Here in zone 7b (average lowest winter temperatures 5° to 10°F), we enjoy productive edible crops and herbs in the garden year-round…with some protection in winter, of course. But we’ve also grown them in colder Maryland winters.

Because I’ve been “advised” by the HOA to stop growing vegetables in the garden (photo, above), they’re now in pots (photo, below) on the fenced deck. (Note to self: next move, no HOA!) Young ‘Aspabroc’ miniature broccoli plants grow in a 20″ pot, where a tomato grew during in the summer. Italian parsley lasts all winter, and sharp-tipped pine cones discourage squirrels.

***Update***: In October, 2021, after my mother passed away, I moved to a small town in northern North Carolina. More property, more nature, woods in the back (where a bobcat and I came face-to-face!), no traffic, gorgeous topography, great friends, just a couple of degrees cooler than Charlotte, and no HOA to tell me what I must or can’t do on my property. 3/1/2024

‘Aspabroc’ miniature broccoli and parsley.

Peas…Yummy!

Peas grow best in the garden’s “shoulder seasons”. That’s when temperatures can be cool to warm, and when frost is no surprise. So, before the end of tomato and pepper season, you can sow a pack of pea seeds next to a trellis and begin harvesting two months later.

Edible podded snap peas and snow peas are absolutely delicious. Many are eaten on the spot. And because they grow vertically, the vines take up little square footage. During the shoulder seasons, in moderate climates, they don’t normally require a protective covering.

Peas growing next to the house, a warmer microclimate.

If you have facilities that can accommodate pea vines, such as a lean-to or a cool greenhouse (Tips #9, #10), this crop can be grown as the temperatures dip lower during the winter months. But there is a point below which the vines will be killed in unheated structures.

Last autumn’s loosely covered pea vines (photo, right) made it just fine through the mild winter and started bearing pods in late winter.

Look for disease resistant varieties when growing any vegetables or greens under cover. Plants are more susceptible to diseases when grown in humid conditions.

Gather Information

Get to know each crop, and how much cold it can tolerate with or without protection from freezing weather. I’ve researched calendars for scheduling vegetables in this zone and have found some of them, compared to my own experience, to be overly conservative. They restrict sowing and transplanting to a narrower period of the calendar than I’m willing to gamble with.

Gardening in a warmer microclimate offers more protection than growing plants out in the open. Planting against a sunny south-facing wall or in a protected corner out of the wind provides opportunities to extend the season.

bees and butterflies feed on nectar in winter

‘Red Russian’ kale in bud.

Kale, collards, spinach, Brussels sprouts, mustard spinach, arugula, leeks, and green onions can tolerate the coldest conditions, within reason. I cover the crops when temperatures dip below the mid 20’s. Even if they’re not covered, they will survive. But I want the plants to continue providing premium quality greens. If not stressed by very low temperatures all day and night, these crops will grow if daytime temperatures rise into the mid 40’s.

Cauliflower and ‘Bright Lights’ Swiss chard need to be covered earlier than other greens. Frost normally won’t kill the plants. But repeated freezing will damage the foliage, halting growth until warmer temperatures (or the protective coverings) return.

These crops and other cool season vegetables won’t need protection if grown farther south. Again, cold tolerance is variety specific, so try new cultivars now and then and see which ones work best for you. For example, ‘Green Magic’ broccoli does well when planted in early spring and again in early autumn. This variety needs a warmer temperature when forming its head. On the other hand, ‘Arcadia’ broccoli can mature in very cold weather, so this is the one I plant later in autumn. Another benefit is ‘Arcadia’s bumper crop of side shoots; in Charlotte, they produced for months.

For More Information

There is so much information online and in catalogs, books, and magazines. But, for local perspectives and information about other growing conditions, check with your agricultural extension office. And speak with helpful vendors at the neighborhood farmers’ market.

Garden clubs, botanical gardens, and garden centers selling seeds, supplies, and transplants sometimes offer classes covering various subjects. My “Cool Season Vegetables and Greens” presentations drew the most attendees. Many of my customers started with just one crop and then returned for more. A healthy addiction!

Keep Records

As you begin new garden projects, place labels with the plants, photograph progress, and take notes for future reference. Add some varieties you’ve never grown before to discover delightful new flavors. Observation of the varieties you’re growing in your garden is invaluable when planning future garden projects. There is no substitute for hands-on experience…and records of successes and failures!

Keeping detailed drawings of crop placement in the garden will help when considering crop rotation. Not growing plants from the same family in the same place every year helps decrease concentrations of pathogens and insects. But, because so many of the cool season vegetables are in the Brassicaceae family, it’s difficult to rotate these crops in our limited space.

Succession planting calls for sequential use of space, maximizing the amount of produce harvested through the seasons. It is especially important to prepare the soil before the fall or spring season, adding fresh compost, aged manure, or planting mix.

For optimal harvests, you’ll need to fertilize regularly as the plants grow. Instead of relying on memory, record the names of the products and when you applied them.

Have all underground utilities marked by your municipality before proceeding and keep a record of their locations. Call 8-1-1 to schedule an appointment.

Headings:

Page 1: Ready For Fall?, Where There’s a Will, There’s a Way (The Advantage Of This Latitude), and Succession Planting: Warm, Then Cool Season Vegetables (Peas, Yummy!, Gather Information)

Page 2: Seed or Transplant? (Seeds, Temperature, Transplants, More Favorites), Crops With Ornamental Edible Leaves (Tender Leaf Kales), Crops That Form Heads, Soil Fertility (The Importance of Microbes), Nutritional Benefits, and Ready For the 10 Tips?

Page 3: Tip #1: Move Tender Plants Indoors, Tip #2: “Quick! Cover Up!”, Tip #3: The Hot Water Bottle, Tip #4: Low Tunnels, Tip #5: Deal with the Wind, Tip #6: Add Christmas Lights, Tip #7: I’ll Have a Double

Page 4: Tip #8: A Simple Cold Frame For Cool Season Vegetables, Tip #9: A Lean-To, Tip #10: The Greenhouse, Finally!

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Soil Prep 101 For Your Vegetable Garden

Apr25

Cool season vegetables and greens.

Finding the Perfect Spot for Your Vegetable Garden

For the purpose of this post, I’ll assume that your vegetable garden will be flush with the surrounding lawn, rather than in a raised bed. However, sound horticultural principles apply to either method. Locate the garden where it gets lots of direct sunlight, and avoid low areas that collect water after heavy rain. Place it close to a source of water.

Now that you’ve found the perfect spot for your vegetable garden, you’re ready for Soil Prep 101. The types of crops you plant in any season are weather-dependent, so make sure weather patterns in your location suit the peppers, basil, kale, or cauliflower.

Although this article concentrates on preparing beds for vegetable gardens, the principles apply to other plants as well, including new shrub borders and flower gardens for pollinators. Page 2 of this article has tips for improving the soil’s tilth, or workability, for most garden projects.

Prerequisites for this class: “How to Prepare the Soil: An Introduction” and “Yes, But Is It Sunny In the Winter?”

Swiss chard in a raised vegetable garden

Swiss chard in a raised bed.

Depending on your level of affinity for precise measurement, you can use either a measuring tape or simple paces to mark the dimensions of your garden. Gardeners who want to indulge in culinary experimentation by growing a wide variety of crops might regret not having made the vegetable garden large enough from the outset. Consider the possibility of expansion in the future.

How Much Sun Does the Vegetable Garden Need?

There is no substitute for sunlight. Without at least 6 hours of direct sun, the results will be disappointing. Anything less than that will reduce and delay the harvest.

Indirect, dappled, and filtered light don’t really count. In fact, during most of the growing season, fruiting plants perform so much better with 7 or 8 hours of sun, minimum! There are other types of crops that can be grown in less than full sun, including leafy greens (lettuce, arugula) and a few herbs (cilantro, parsley).

Layout

Tomato.

Someone out there is asking, “Do I run the rows (the long axes) east-to-west or south-to-north?” Good question! If your plans include growing several tomato plants and maybe some pole beans on a trellis, and you prefer one long plot that is accessible from both sides, I recommend east-to-west.

Long-term plants (tomatoes, peppers, etc.) will continue to get good sunlight all season. Spaced properly, they won’t cast as much shade on each other, especially as fall approaches and the sun sinks lower in the sky. But, if your garden receives sun all day, it won’t make much difference to main season crops.

Cool season crops, grown from fall through early spring, however, will get more sun when planted east-to-west. They’ll face the sun all day even though the days are short.

Taller plants should be planted on the north side of any plot (northern hemisphere), so they don’t shade smaller plants nearby. Some varieties of staked indeterminate tomatoes can grow 8′ tall!

lettuce basket, a portable vegetable garden

Lettuce growing in a basket.

On properties where spatial considerations are limited, do what you can to provide enough direct sun to those crops you can’t live without. Your crops might not be lined up in neat rows, but rather planted individually in a sunny corner over here and another by the back gate. Doesn’t matter. Do what works for you!

Container-grown crops, such as this lettuce basket (photo, above), can be moved around as conditions change.

Multiple Vegetable Garden Beds

With ample space, a series of garden beds can be laid out in a grid. When deciding where the plants will go, always keep in mind that you want to prevent tall plants from shading short plants, with few exceptions. Using straight pathways makes maneuvering the wheelbarrow and equipment easier.

Crops that prefer cooler, part-shade conditions as the weather warms can be planted between the taller plants or in the partial shade they cast. Those include late spring lettuces, arugula, cilantro, and spinach.

Savoy cabbage.

Having several plots allows for crop rotation, planting one family of plants in Plot A this year, in Plot B next year, and so on. This helps prevent the soil from being severely depleted of certain micronutrients and from allowing populations of insects and diseases to build up.

The nightshade family (Solanaceae: tomato, pepper, eggplant, potato), the cucurbits (Cucurbitaceae: cucumber, summer squash, zucchini, melon, pumpkin), and the brassicas (Brassicaceae: broccoli, cabbage, cauliflower, kale, Brussels sprouts) are groups of plants that benefit from being rotated every 4 or more years.

To clarify, one member of a family (tomato, for example) should not be planted where any member of that family (tomato, pepper, eggplant, potato) has grown in the past few years.

This is a good reason to keep a record describing where you plant each crop every year, as well as documenting successes and losses. Knowing the family names that crops belong to also helps with crop rotation.

Seed Or Transplant?

Don’t go overboard if this is your first attempt. You’re not obligated to germinate every pack of seeds you bought. There’s always next season. Most seeds will remain viable for a few years if kept dry and cool.

Starting out with young tomato, pepper, or slow-growing parsley transplants might be more practical than growing them from seed, even though it is more expensive. You’ll find them at garden centers, farmers’ markets, and local hardware stores, and the growers often have good suggestions for cultivation.

If you’re late getting the vegetable garden going, transplants will save you several weeks of growing time. You can always supplement with fast sprouting varieties of seeds, such as those mentioned in the next section.

Starting plants from seed is a welcome challenge to many and is a source of fascination for children—and for adults, too. Don’t laugh, but, for me, it’s a thrill when the catalogs start showing up in the mailbox. I would never discourage you from exploring this facet of gardening. And, of course, there are so many excellent varieties available from seed that never show up in retail stores as transplants.

Seedlings For Vegetable Gardens Need Sun

Seedlings of fruiting crops need at least 6-8 hours of direct sunlight for strong growth. Use clean pots, pasteurized seed starting mix, and a waterproof tray. Provide the proper temperature for germination.

If you don’t have very sunny windows or a greenhouse, consider starting seeds under shop lights with daylight tubes. I use 4′ long fixtures that hold 2 tubes each. Seedlings growing very close to the tubes—only a few inches away—grow strong stems and roots.

Lettuces, arugula, and other leafy greens tolerate fewer hours of sun, although they appreciate full sun during the cooler months.

Avoid starting seeds too early in the season. This could result in leggy, weak plants that might not perform up to par in the garden.

Broccoli ‘Happy Rich’ and Arugula ‘Astro’ seeded into cell packs (late winter, 2022).

Seeding Directly Into the Garden

Some crops grow easily from seed sown directly into the vegetable garden. Peas and beans, for example, and radishes, beets, and carrots are just a few species that can be planted right into prepared ground. Dinosaur kale, mustard spinach, mesclun, leaf lettuce mixes, zucchini, spinach, and cucumbers are more crops that can be directly seeded.

Read all the information on the packet, paying special attention to when to start and how deeply to sow the seeds. Although these crops germinate readily, gardeners must still watch out for pests, both above and below ground, and turns in the weather.

Spacing the Plants

It’s important to calculate how much square footage each of your plants requires, or at least to get a rough idea. On graph paper, map the proposed garden to scale. Use the plants’ spacing recommendations found on the label or the seed packet for the amount of space needed.

With a 1/4″ grid, each square can represent 6″ or 12″ of garden space. The diagram is optional, but it can help in future years when considering crop rotation.

It’s better to have more than enough room rather than not enough; plants don’t respond well to crowding. The seemingly large gaps between the major crops can be interplanted with “ephemerals”—those plants that grow quickly and are harvested before the majors achieve full size. Examples include radishes and lettuce between tomato plants, or green onions and beets between autumn-grown Brussels sprouts.

If It Looks Like This…

Clay soil shrinks as it dries, creating surface cracking.

Soil that dries as hard as a brick is impossible to work with. You can thoroughly water the area the day before or start digging a day or two after a good rain. Avoid digging or walking in the garden when the soil is wet. This compresses the soil, squeezing out tiny channels of air space that are critical for healthy root growth.

Sandy soil that drains too fast should be amended with copious amounts of organic matter. Bagged topsoil is also available, but quality varies widely. The tiny clay particles in clay loam help hold water and nutrients in the soil.

In a large vegetable garden, plan for pathways every 4′ or 5′, and restrict foot traffic to those areas. Use pavers, flagstones, pine bark, or even that old pile of bricks for the pathways. You can get very creative with stonework, and your garden can be the neighborhood show-stopper, but don’t lay out the stones until the end of the soil prep process.

Let’s begin! Please turn the page…

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Headings

Page 1: Finding the Perfect Spot for Your Vegetable Garden, How Much Sun Does the Vegetable Garden Need?, Layout, Multiple Vegetable Garden Beds, Seed Or Transplant? (Seedlings For Vegetable Gardens Need Sun, Seeding Directly Into the Garden), Spacing the Plants, and If It Looks Like This…

Page 2: Remove Sod, Tilth, Soil Prep (The First Dig: Loosen the Clay, The Second Dig: Add Drainage Materials, Organic Matter vs. “Organic”, The Third Dig: Add Organic Matter), Fertilizers, Rake Smooth and Pave, Agricultural Extension and Soil Tests (To Lime Or Not to Lime, and What is pH?)

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