Protecting root and stem crops with a thick, insulating blanket of winter mulch is the easiest – and cheapest – way to stretch your homegrown harvest into January and February. You don’t need to buy or build any structures like cold frames or mini hoop tunnels, and you can typically source your mulching material for free by using chopped leaves or straw. It’s a technique I talk about in my books, The Year-Round Vegetable Gardener and Growing Under Cover: Techniques for a More Productive, Weather-Resistant, Pest-Free Vegetable Garden.
Why use a winter mulch?
Each autumn, we gather about forty bags of leaves from our property. Before they’re raked and bagged, we run over the leaves with the lawn mower to shred them into small pieces. Whole leaves tend to mat together, while shredded leaves form a light, fluffy mulch. Of course, shredded leaves also make an excellent soil amendment and any extra leaves can be dug into your garden beds to improve the soil. I’m also lucky enough to be the recipient of about twenty bags of additional leaves from my dog-free neighbours – which are then put to good use in my winter garden and leaf compost bin. Don’t be shy about gathering leaves from your friends and family as there are so many ways to use them in the garden. (Check out this excellent article from Jessica)
Straw is also a great mulching material, but it can cost up to $10 per bale, depending on where you live. But, if you promise not to tell anyone, I’ll share a little secret. In late October and November as supermarkets, hardware stores, and homeowners clean up their exterior autumn and halloween decor, they often have straw bales to discard. Keep your eyes open and a tarp in your trunk for unexpected bales. I’m usually lucky enough to source around a dozen bales of straw each autumn – for free!
How to apply a winter mulch in the vegetable garden
Winter mulch is best applied before the ground freezes. This will allow easy harvesting throughout late fall and winter.
- Mulch. After you have gathered your materials, add a one-foot thick blanket of mulch to garden beds where there are still root vegetables like carrots, beets, parsnips, and celeriac, as well as stem crops like leeks and kohlrabi. This layer of insulation will ensure the soil doesn’t freeze deeply and the crops remain harvestable throughout the winter. This technique is best for gardeners in zones 4 to 7. Those in colder zones should top mulched beds with a mini hoop tunnel to help further insulate the crops and prevent deep soil freezing.
- Cover. Cover the mulched beds with a length of row cover or an old bed sheet. This holds the shredded leaves or straw in place and prevents them from blowing away during winter storms.
- Secure. Weigh the cover down with a few rocks or logs, or use garden staples. Insert the staples directly through the fabric and into the soil to anchor the fabric in place.
- Mark. If you live in a snowbelt – like me – use bamboo stakes to mark your beds. It can be awfully difficult to find the right spot in mid-winter when there is a foot or more of snow covering the garden and you’re wandering around looking for your carrots! (Trust me on this one.)
Bonus tip – Cold-tolerant leafy crops like kale and spinach can also be protected with a simple mantle of evergreen boughs. Kale will remain harvestable in most regions throughout winter and spinach that is seeded late in the season will overwinter as baby plants beneath the boughs. Remove the branches once the weather is reliably above 40 F (4 C) in early spring.
Top crops to winter mulch:
- Carrots. Carrots grow best in light, stone-free soil of average fertility. In late autumn before the ground freezes, cover your carrot beds with at least a foot of shredded leaves or straw. For the best flavor, pick a super-sweet variety like ‘Ya-ya’, ‘Napoli’ or ‘Autumn King’.
- Parsnips. Like carrots, parsnips will need an deep layer of shredded leaves or straw for winter harvesting. Delicious garden parsnips don’t reach their full potential until they have been touched by several hard frosts, so don’t be too eager to harvest. Personally, I don’t even dig the first root until Christmas and we continue to harvest them into early spring.
- Celeriac. Because celery is an essential aromatic in so many dishes, I like to keep a homegrown source handy. For six months of the year, we have the fresh stalks of garden celery, a 2 to 3-foot tall plant that can also be mulched in autumn to blanch the stems and extend the harvest by about a month. The other half of the year, we have celeriac, also known as celery root to supply us with a bumper crop of knobby, brown roots from November through March.
- Kale. Kale is the superstar of the winter garden! It’s extremely hardy, easy to grow, incredibly nutritious and boasts a flavor that improves dramatically with the arrival of the cold weather. We grow many varieties of kale, but our favourites include ‘Lacinato’ (also called dinosaur), ‘Winterbor’ and ‘Red Russian’. It can be winter protected in a high cold frame, mini hoop tunnel or with a mulch-like straw. For compact cultivars, simply cover with your insulating material. Tall kale plants can be surrounded by wooden stakes that are wrapped in burlap to create a ‘tent’, which is then filled with leaves or straw.
- Kohlrabi. An odd-looking veggie, kohlrabi is under appreciated by many gardeners. It is easy to grow, has crisp apple-shaped stems and boasts a mild broccoli or radish-like flavor. We plant it in late August for an early winter harvest, mulching the kohlrabi bed with straw in mid-autumn. The rounded stems won’t last all winter, but we eat them well into January – or at least until we run out!
Do you use a winter mulch in your garden to extend the harvest?
I’m not growing any root crops currently, but I use straw on the herbs (Love the stuff.)
How cold can the root crops take it before they get freeze-dried or turn to mush…or is there no limit on min. temp?
Hi Alan.. straw is a great insulator! I often use it on herbs, celery and even big kale plants. There is a cold limit, but I’m in zone 5 and have no issue winter harvesting root crops all winter. Certain root crops – carrots, parsnips, beets, for example – are more cold tolerant than others, like radishes, so I recommend concentrating on those. The earth protects them quite well and the additional layer of straw mulch keeps the soil from freezing for easier harvest, as well as providing further insulation. Crops like celeriac that are above ground need to be well mulched as they are prone to freezing damage and then – as you mentioned – can become mush.
We followed this advice one winter with mixed results due to the weather. There was a thaw in Jan. with rain followed by freezing temperatures again. The old bed sheet covering the thick layer of mulch froze to the ground and mulch. It ripped when I wanted to pull it up to harvest. Mother Nature has a way of thwarting ones plans.
Judy Fulton says
Be careful of straw contaminated with herbicides. I opted for certified organic because I was warned that contaminated straw can put a garden bed out of commission for years.