Top 10 Tips for Growing Vegetables in Winter

Are you a dedicated vegetable gardener?  If so, I know you thrive on growing plants. Do you marvel at tiny seeds sprouting and growing into vegetables? Nothing is better for the soul or our stomachs!

20 years ago, I embarked on the journey of winter growing. I wanted to extend our harvest seasons and to have vegetables over the winter. I wanted to have early spring crops. I wanted—nature laughed!

So, here are some tips and strategies based on what I have learned (and continue to learn) about growing in the winter months. Winter is a challenge for us here in Delaware, because our days are shorter, and the night-time temperatures are below freezing.

Look for cold-hardy varieties that can handle the level of protection that you can provide. Adjust your expectations of how quickly things will grow. Supplemental heat makes a huge difference, but you have to evaluate the cost of heating compared to what you get out of it.

Remember, patience is key! As you already know, every growing area has its own micro-climate and ecosystem, so what works in one place may not grow in another. We struggle with our clay soil and add compost on a regular basis. You may have a different kind of soil with different needs.

Here are 10 tips and strategies for successful winter gardening:

1. Light — as much as possible! Anything with a flower needs at least 10 hours of daylight in order to flower, pollinate, and produce. However, plants that do not flower can get by on 4-6 hours of daylight.  Good thing, because the winter months are often cloudy, and the light is often diffused for much of the day.

In Delaware, where we are, we lose our 10-hour mark on November 15, and go back above 10 hours on January 26. Google knows the answer to your 10-hour marks.

So, what grows in lower light levels? Lettuce, arugula, chard, collards, kale, mustard greens, mizuna, spinach…you get the idea. The leafy greens. Plus, you can grow beets, carrots, radishes, carrots, daikon, turnips.  They grow in the dark, underground, but need light to feed the top growth.

2. Wind protection — Winter winds are ferocious on plants! Some sort of protection is necessary, keeping in mind that you want to let in as much light as possible.  You can build a cold frame, cover with row cover, build a lean-to, use container pots in a sun room in your house, build a mini-greenhouse with glass walls and roof.

Anything with glass or greenhouse plastic will amplify any sunlight and help warm the plants up during the day. Night-time temperatures, though, can get pretty cold. Each unheated layer that you give the plants gives you about 4 degrees of protection. If it goes down to 20, you will have 24 degrees inside your area, without supplemental heat.  If you add a row cover over your plants plus the outer cover, you have 8 degrees of protection.

3. Growing time without heat — This is a tough one. Basically, you need to have your plants at close to maturity before you go to fewer than 10 hours of daylight (which usually coincides with cold nights and cooler days). Your plants will sit there and not grow very much until you get above that magic 10-hour mark (which coincides with better daytime temperatures and slightly higher night time temperatures). You will be able to harvest from your plants, but they will not be growing very much to replace what has been harvested until early March.

4. Growing in a lean-to or mini greenhouse. I get it, I do. The temptation to put in lots of shelves and pack that space with seedlings and plants is overwhelming.  Especially if you are putting a little heat in there to promote growth. However, plants on lower shelves get less light than those on upper shelves. Consider rotating the plants on the shelves to give them access to light.  Container pots that can be staggered in their stacking are a great way to use your vertical space and still provide adequate light.

If you have a structure up against a house wall, it gets the benefit of residual heat from the house. Have the structure so that you are south facing for maximum sun exposure.

It’s hard to believe, but you also need to keep in mind venting on sunny days, as it can get too warm too quickly in a little house. You will get a build-up of condensation, which drips on the plants and can cause mold. A fan, or a way to crack a door or window, is helpful to keep the air circulating and bring some fresh air into the house.

5. Where do those aphids come from? You have seen them appear all of a sudden on house plants or in a greenhouse. They are a complete nuisance in a closed setting. Proper air circulation and venting help a lot in keeping aphids out of your plants. Inspect your leaves regularly and wash off promptly. We use a peppermint solution which helps if those pesky critters show up. We also have fans which run 24/7 in our tunnels.

6. Growing times — Even with heat, everything takes a little longer. About 25-40% longer. Without heat, it takes about 3x longer. If you are working without added heat, plan to start seeds in early August to early September, so that plants are at maturity by mid-November. You can then harvest from the plants while they sit there. Depending on the weather, of course, the plants will start growing again in late February and early March.  

Winter growing is definitely a more relaxed pace. EXCEPT—late spring, when we get those freak warm days! It shoots up to 85 degrees on April 10, and the cilantro says, seed time, and bolts.

7. What grows best in the winter — cold hardy plants! Many of the herbs, leafy greens, root crops, some of the brassicas. Here is a partial list; depending on your particular circumstances, you will add or subtract from the list.

Parsley, cilantro, sorrel, romaine, green or red leaf lettuce, kale, chard, collards, mizuna, mustard greens, sprouting broccoli and cauliflower, spinach, beets, carrots, radishes, daikon, turnips, rutabagas, scallions, Brussels sprouts, cabbage.

8. Days to maturity — In general, we look for plants that are relatively quick growing—under 55 days. For the plants which take longer, start them in July or August or early September, so that they are close to maturity or at full maturity by early November. For example, Hakurei is a small turnip with 38 days to maturity and Purple Top White Globe turnip is 50 days to maturity. Keep in mind you need to add 20% more days—so 45 days for Hakurei and 60 days for Purple Top-- to maturity, as everything just grows more slowly.  As long as the ground does not freeze, either one is fine.  Brussel sprouts, on the other hand, take 110 days! These you need to start early—June 1, or earlier-- so they have time to mature by early November. Many of the brassicas are cold hardy, but have huge leaves, so they take up a lot of space.

9. You have time to harvest — If you cannot get to a crop today—or even this week—it’s ok. The plants hold steady, unlike the summertime where plants can be over-mature in less than 24 hours! So, beets and carrots can sit in the ground until you are ready, and lettuce can wait for a week or so. It’s definitely a more relaxed schedule. One of the great benefits of winter growing!

10. Heat — Heat is a game changer. You go from plants sitting there from November through February to continuously growing (still slower than summer, but let’s be realistic). Night-time temperatures are key. If you can heat to 35, you keep the plants from going through the freeze-thaw cycle. Only a few plants keep growing at 35.  If you can heat to 45, then most of your cold-hardy plants will keep growing, just slowly. To get plants growing at close to May or September rates, you need night-time temperatures of 55. The cost of this is probably not worth it for the home gardener, depending on your heat source. It just means planning ahead so that you have crops to harvest.

High tunnels at Highland Orchards

Winter growing (Swiss chard)

Winter growing (scallions)

Has this given you lots of ideas? I hope so! It is so much fun to have plants growing in the middle of winter, when everywhere outside is dormant. There is the added bonus of being able to eat wonderful, fresh vegetables all year. Look at how much space you have to devote to a winter garden, and plot out what works for you. What will give you the most pleasure to harvest?

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