This page is my attempt to get you maritime gardeners interested in growing winter vegetables! C'mon; it's fun, easy, and good for you!


Why have a winter vegetable garden?

I tend to think that a trip down the produce aisle in winter will let you answer this yourself. But I'll tell you why I do it.

As is the case with summer vegetables, fresh from-the-garden produce simply tastes better than its supermarket counterpart. Because it is harvested closer to the time it is consumed, it is higher in vitamins (this is probably even more true in winter than in summer, since so much of the commercially available winter produce is grown in the southern hemisphere). The eating quality is often remarkably higher: For instance, many vegetables store more sugars when they are exposed to cold temperatures. Also, a lot of winter vegetables are poor shippers; so if you want quality leeks or kale you have no choice but to grow them yourself. In addition, you know what has, and hasn't, been sprayed all over your own plants!

All of the above is true. But, for me, the bottom line is simply this: I enjoy it! There is something incredibly satisfying about pulling a delicious carrot out of January's mucky soil, or cutting fresh Brussels sprouts when the snow is on the ground. I suppose, in the end, it is my way of thumbing my nose at Old Man Winter.


Sowing vegetables for Fall, Winter, and Spring harvest

Some quick notes: I garden in Sumner, Washington, in the USA. Sumner is roughly parallel with Tacoma (47 degrees north latitude), and experiences the same strong maritime influences as most locations west of the Cascade mountains. Being about 15 miles from Puget Sound, though, my experience has been that my garden's daytime high temperatures are a few degrees higher, and my nighttime temps a few degrees colder, than in many locations closer to Puget Sound.

Our winter weather is rainy the vast majority of the time. The mean low temperature from late December to early January is a bit over 33F, with an average daytime high of about 48F. When we do get frost, usually the nighttime temperature only dips to between 25F and 30F. About once a winter, though, we will have a short period where we'll get down to between 10F-20F (which makes us USDA zone 8).

Plant Sowing date Hardy to Notes
Arugula August 15-September 15 15F/-9C Holds up reasonably well to rain
Beets Best in July 1-10, will work if sown until the 20th 20F/-7C Can go colder with mulch
Broccoli fall/winter Anytime in June 25F/-4C (?) Rain will probably kill it before the frost does
overwintered July 15-August 1 10F/-12C these are the biennial sprouting broccolis
Brussels Sprouts May 15 0F/-16C Seriously, these taste nothing like the store-bought ones
Cabbage (for winter) June 1 5F/-14C (hardiest varieties) I haven't grown the spring cabbages like First Early Market, so I really don't know the timing
Carrots July 1-15th 15F/-9C With mulch, these can be depended on to overwinter. An August 1st sowing still give useable, but smaller, roots. With carrots there seems to be big differences that are just related to how particular varieties grow as the days get shorter.
Cauliflower fall/winter June 1-30 25F/-4C (?) Rain and slugs tend to do mine in before the cold does
overwintered July 15-August 1 5F/-15C Takes soggy soil somewhat better than sprouting broccoli
Chard Up until early August 20F/-7C Even if the plant dies back, often the crown survives to regrow in the Spring
Claytonia/Miner's Lettuce August 10-25 At least 11F/-12C Fast growing, compact, does well under cover
Corn Salad/Mache August 20-September 1 At least 8F/-13C Seems to thrive unprotected in our rainy wet winters
Cress, Garden (Upland) By late August At least 15F/-9C Biennial plants can be started as early as late spring
Escarole/Endive August 1-10 Reportedly 5F/-15C Good cloche candidate, since wetness is more of a problem than cold. Bitterness decreases with frost, and varies from variety to variety.
Favas September,October 10F/-12C I sow in late September. I've gotten away with sowing them in November; they will grow a little even in winter, during any spells when temps are above freezing!
Kale July 1-15 At least 8F/-13C Needs no protection
Kohlrabi July 10-20 15F/-9C Can go lower with mulch or under cover
Garlic September,October At least 8F/-13C I plant in late September. Basically, if the ground isn't frozen, you can put them in.
Leeks April-Early May At least 8F/-13C Big differences between varieties in terms of hardiness and bolting date. This entry reflects my experiences with Durabel.
Lettuce August 1-10 24F/-4C Another good cloche candidate
Minutina August 10-25 ~ 15F/-10C Unusual, almost succulent leaves
Mustard July 15-August 10 15F/-9C Hardiness is variable, depending on variety
Onions Most types August 10 0F/-18C Most overwintered onions dry down in June. Waterlogged winter soils can be a problem for all overwintered onions
Walla Walla sweet September 1-15 Reportedly -10F/-24C Walla Wallas dry down in July.
Scallions June-September At least 10F/-12C This applies to Allium cepa types of scallions. A. fistulosum types are much hardier and non-bulbing, but also are less tender and hotter in flavor.
Parsnip June 15 - July 1 At least 8F/-13C It's fun trying to keep these seeds damp until they sprout!
Radicchio July 15 Reportedly 5F/-15C Leaf types are easier and more reliable. Don't dawdle in sowing this one!
Radishes Through September Uncertain Various rots and soil dwellers spoil mine by midwinter, even though the plants are still alive
Spinach August 1-15 At least 8F/-13C Under a cloche they can be depended on to overwinter

These dates are what has worked for me in my garden. If you live in a milder microclimate than mine, or live further south, a later sowing date will be appropriate for many of these. For example, people down in Oregon tend to sow winter crops later than I do, because they have a slightly longer season (and more daylight after the equinox). A good practice the first couple years is to make multiple sowings, 7-10 days apart, to help give you a feel for the proper timing at your location, which can be important in terms of final plant size. In addition, some of these plants are photoperiodic, and will bolt to seed if sown too early.

You can get away with later plantings of non-"bulbing" (for lack of a better word) veggies; just don't thin as much. But root vegetables and kohlrabi need a certain amount of time to reach a useable state.

Note that I usually sow the seed directly into the garden. If you prefer to raise transplants, they should really be started two or three weeks earlier than I have listed. Transplanting, no matter how carefully done, shocks the plant. It is sometimes advantageous to raise transplants, though, either because your garden space is limited, or because you find it easier to manage the environment needed to assure good germination.


Cultural Considerations

Dampness

In the Maritime Pacific Northwest, many otherwise-hardy plants will not survive over the winter. Why? Because our consistently damp winter weather provides a haven for molds and fungi. Leafy greens are especially succeptible. Escarole, for example, can easily handle temperatures below 10F; but it rapidly will rot if kept constantly damp. The solution? Raised beds, combined when possible with cloches or a PVC hoophouse.

Raised beds can be elaborate affairs, framed with wood or plastic lumber specially manufactured for this purpose. In my garden, I followed this simple technique (which I borrowed from Steve Solomon): I first tilled the entire area. Then I marked where the paths would be, and shoveled a bit of the dirt from the areas marked as "paths" onto the areas selected to be "beds". Rake the beds smooth, and you're done! As long as you never step on the beds, and don't leave them bare through the winter, you probably won't have to remake them for many years.

Cloches are essentially plastic tents for your plants. They can be easily built from all sorts of materials. The ones I use are made with 1/2" PVC pipe and a 10'x20' sheet of 3-mil clear plastic. Simply cut the ends of the PVC at an angle (to make a point), bend it into a croquet-hoop, and push both ends into the ground. Place these hoops every 3-4 feet, oriented over your garden row or bed. Then, just lay the clear plastic over this framework. You've got a cloche! The plastic can be held in place by weighting down the sides (I use milk jugs filled with water); you can also buy "cloche clips" to hold the plastic onto the PVC pipe (or make your own using 3/4" poly pipe). Be sure to leave one end of your cloche open for ventilation.

PVC hoophouses are like a giant cloche. They are a bit more involved to build, but I think they're worth the effort. For one thing they allow better air circulation around your plants than cloches do. Also, since you can walk into a PVC hoophouse, harvesting during a downpour is a far more pleasant experience.

Mulch

Mulch accomplishes several purposes. It prevents soil compaction caused by constant winter rainfall. Also, it evens out the swings in soil temperature that can come in winter. This means, among other things, that you can still get access to your root vegetables, even when the unprotected ground of your garden is frozen. Mulch cuts the amount of light that reaches the soil, so winter weed growth is inhibited.

If you live where the soil regularly freezes, mulch is a necessity if you want to harvest winter vegetables. The temperature under the mulch will be higher than in free air, as long as you apply the mulch before your ground is frozen. In heavily-mulched winter gardens, some folks find it easier to access their vegetables if they lay a floating rowcover over the plant tops before they spread the mulch.

A good mulch will help trap layers of air above the ground, which increases the insulation value, yet still allows some air circulation. Many people choose straw for this reason. A problem with straw, though, is that it can contain lots of weed seeds. In the northeastern US, saltmarsh hay is often available. Leaves can also make a good mulch, but they tend to pack down in the constant winter rain (which decreases the insulation value). If you use leaves, you might want to lay a sheet of plastic over the top.

Mulch should be removed in late winter or early spring, both to allow the soil to warm, and to not deplete the nitrogen availability to your early spring plantings.


Cover Crops/Green Manures

Cover Crops are a very important part of proper garden management. Of course, having a winter garden complicates the planning involved! But it can be done, and is fairly straightforward once you develop a garden rotation scheme.

Due to the importance of this topic, I don't want to give it less than its due. So I'm going to recommend that you read an article I wrote on this subject, Cover Crops and Green Manures.


References

Hopefully this page has at least piqued your interest, and has provided enough information for you to get a winter vegetable garden going. If you're interested, you might also want to check out some of the many articles we have that talk about winter gardening. Also there are a number of good reference books on this subject:

Gardening Under Cover [affiliate link], by William Head. This books subtitle is "A Northwest Guide to Solar Greenhouses, Cold Frames, and Cloches", which says it better than I could.

Growing Vegetables West of the Cascades [affiliate link], by Steve Solomon. This is not strictly a book on winter gardening, but it is an invaluable reference for the year-round vegetable gardener.

Winter Gardening in the Maritime Northwest [affiliate link], by Binda Colebrook. This book has lots of useful information. Sometimes you have to wade through the flights of fancy (I get the impression Ms. Colebrook was a child of the 60s), but it's definitely a worthwhile, informative read.

Also, be sure to pick up a copy of the catalogs from Territorial Seed Company and Johnny's Selected Seeds. Not only are they the best seed sources for the specific varieties you'll need in your winter garden, but their catalog is full of good cultural information, year-round.


All contents © Travis Saling
This page was last updated December 8, 2013