December is a dreary month for many outdoor gardeners — time to huddle indoors, devour the seed catalogs and dream of spring. Of course there are a few devoted and well-organized souls who do not allow the cold season to dampen their passion. They keep the garden fever going throughout the darker days.

In our local gardening group, one of these winter heroines is Barbara Miller. Barbara bubbles with enthusiasm for all things organic, alive and growing. During the summer, her 4000 square feet garden overflows with every imaginable vegetable, enough to supply many neighbors as well as a local gourmet restaurant. The secret of all that fertility is mulch – lots of mulch.

For most of us, mulch means a layer of protective material a couple of inches deep. That is small potatoes for Barbara. Throughout the growing season she is always on the lookout for organic material to add to her garden beds and paths. Barbara is not too fussy. Sawdust and shavings from wood shops, spent hay and straw from the roadside or local farms, coffee grounds from coffee stores, grass clippings from the neighbor’s yards, even pine needles — all and everything is scavenged for her garden.

Barbara is a proponent of the “no-dig” school of organic gardening. Even when sowing seeds, she turns over only a few inches of soil and loosens it a little to allow the seeds to germinate. Planting vegetable starts is even simpler: she pushes aside the mulch, digs a hole and pops in the plant. Every seedling is surrounded and protected by layers of organic matter, growing deeper as the plant develops. After ten years of mulching with little or no soil disturbance, Barbara has generated over 12 inches of moist crumbly dark humus: all she needs to grow amazing amounts of organic produce.

After the fall harvest, as the garden is cleared, Barbara gets to work on her winter project – maxi mulching. From October onward, her mulch scavenging really takes off. Barbara puts a sign out on her street asking people to donate their plastic bags of dry leaves. Last year, over 600 bags of leaves were left outside her door. She takes the plastic bags and tightly packs and layers them on specific parts of her garden, without emptying the contents. As Barbara puts it, “When I say mulch, I mean layers of bags two or more feet deep.” By November, her garden begins to look a bit like a municipal dump.

She pays particular attention to all her roots crops planted in late spring – potatoes, rutabaga, turnips, carrots, celeriac, parsnips and beets. When the plant leaves die back, she covers the roots with the insulating bags. The ground does not freeze. Instead, the bags creates a virtual root cellar in which the damp soil keeps the roots crisp and fresh; the moderate cold makes sure the veggies taste sweet. To harvest her winter carrots for example, she digs through the snow, lifts her bags and pulls the roots straight out of the soft ground.

Her tender perennials are treated in a similar manner. Some she insulates where they grow. Others she moves from their summer home and buries in the ground on the north side of her garden shed, covered with her favorite leaf bags. The bags do double duty, protecting the plants from cold but also making sure the soil and roots do not dry out in Colorado’s winter sun and wind.

I asked Barbara what happens to all those bags of maxi mulch: “In February or March,” she informed me, “I open up the bags and spread the leaf mulch all over the garden. So it doesn’t blow away in the wind, I cover it with hay. That helps it compact down.” What happens next is one of nature’s miracles. In short order, the worms pull the leaves down into the ground, chew them up and create another layer of fertile leaf mold. By summer the leaves are all gone.

One question springs to mind about the effects of maxi mulching: does preventing soil from freezing foster more soil borne diseases? When I asked Barbara, she said she had never thought about it. In her vigorously growing garden, disease is not a problem. This may be because her soil ecology is so extraordinarily healthy.

As Barbara says, “When I lift the bags of mulch in the depths of winter, the earthworms are writhing under there.” Massive colonies of worms are a clear sign the soil food web is vibrant and whole. Keeping the soil cool but not frozen may generate a more consistent growth of microbial life. Many soil bacteria are vulnerable to freezing and take time to regenerate as the soil warms up in the spring. Barbara’s mulching protects these colonies and give her a jump-start to the growing season.

Talking to Barbara makes me rethink my meager mulching program. I am going to keep an eye out for free organic matter, start scavenging for more bags of leaves and pile that maxi mulch on deep for the winter. I am sure my soil will be grateful.