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Mulch? In the winter? You betcha.
Mulches — particularly organic ones — are gardening stars. But when mulches are touted, we usually hear about benefits that are specific to the growing season. Mulches, Wikipedia tells us, “retain moisture in the soil [which is particularly helpful during droughts], suppress weeds, keep the soil cool, and make the garden bed look more attractive.” Right. So what’s the point of mulching in the winter? There are actually five very worthwhile reasons to spread some mulch before the snow flies.
1. Extending the Growing Season
Mulching before the ground freezes helps keep the soil warmer, which prolongs your growing season. This is especially valuable for cool-weather root crops. When mulched, veggies like beets, parsnips, carrots, kohlrabi, radishes and turnips can survive hard frosts.
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You can certainly fork up all your root vegetables before any frost, but it pays to leave them in the ground. These vegetables increase their sugar production as a natural response to the cold. Since sugar freezes at a lower temperature than water, the sugars act as a kind of natural antifreeze. As might be expected, the sugars also increase the sweetness and flavor of these vegetables, making a late harvest extremely worth your while. However, a word of caution: If you live in a cold zone where the ground freezes through, you should fork up your root vegetables before a serious cold spell. Otherwise, you’ll need a pickaxe out there!
2. Protecting Perennials
When I think about mulching perennials for the winter, my mind goes to flowers. But, of course, there are perennial herbs and vegetables, too. Artichokes, asparagus, horseradish, rhubarb and sunchokes would appreciate a toasty layer of mulch, as would any herbs that function as perennials in your hardiness zone. And don’t forget about your berries, especially the low-growing strawberries.
3. Minimizing Frost Heave Damage
While mulch protects perennials against extreme weather, it can also prevent root damage caused by frost heave. As unprotected soil goes through freeze/thaw cycles, it expands when its moisture freezes. This expansion can push the soil upwards and may push plant roots up at the same time. If the exposed root freezes, it can be damaged. Mulch moderates soil temperature so that the freeze/thaw cycles aren’t as marked or as frequent, minimizing heave.
4. Improving the soil
Any type of mulch can help protect soil from the heavy winter rains and excessive snowmelt that can cause soil erosion and compaction. And, of course, organic mulches improve the soil by releasing nutrients and organic matter as they break down. This is true regardless of whether the mulch is applied in late fall or during the growing season.
That said, certain types of mulches are more beneficial to both soil and plants if they’re applied in late fall or winter. As this article points out, woody mulches (wood chips, bark, or sawdust) need nitrogen in order to break down. When applied in the summer, woody mulches can tie up the soil’s nitrogen resources as they decompose, making that nitrogen unavailable to plants in the area. But if woody mulch is applied in late fall or winter, it will begin breaking down before plants need the soil’s nitrogen resources.
5. Suppressing weeds
One of the best things about mulch is its ability to suppress weeds. It may seem pointless to apply mulch in the winter for weed control. But come spring, that mulch will be covering the last season’s weed seeds, preventing them from sprouting.
Choosing Winter Mulch
The nifty thing about mulching for winter is that there’s plenty of free mulch for the taking. Leaves, of course, are naturally abundant at this time of year, but you can use other yard and garden debris too including grass clippings, pine needles, evergreen branches and boughs, and pulled vegetable plants that are destined for the compost bin. As an added benefit, garden debris provides a cozy habitat for crickets, which enjoy chowing down on weed seeds.
In addition to free mulches in your own yard, check with stores and businesses that use straw bales for fall decor. Once the cardboard turkey and maple leaf displays get the heave-ho, the straw bales will need to go somewhere, too. Why not pop them into your garden instead of into the trash? (Be wary of hay bales, though, which contain more weed seeds than straw bales.)
Applying Winter Mulch
As stated above, applying mulch before the ground freezes can extend your growing season and contribute to better tasting root vegetables. On the flip side, applying winter mulch before winter is here to stay can attract nesting rodents. When you apply winter mulch in your own garden comes down to personal choice. Consider what type of mulch you’re applying and what your primary reason is for mulching. If you mainly want to extend the growing season, then it makes sense to mulch before the ground freezes. But if you’re mulching to suppress weed growth in the spring, then waiting for the ground to freeze is the better option.
Once you actually start mulching, aim for a depth of about 6-12 inches. If you live in a blustery, wintry zone and you’re using lightweight mulch like shredded leaves or straw, it’s a good idea to cover that mulch to prevent it from blowing away. Use an old bed sheet or, if you use them, a fabric row cover, and anchor that fabric with bricks, logs, or ground staples.
Have you ever used mulch during winter? What advice would you add? Share it in the section below:
