By Denise Seghesio Levine, U. C. Master Gardener of Napa County
Many years ago I read a garden book that explained that the key to growing healthy plants is growing healthy soil. Rather than watering and caring for just my vegetables, I learned I needed to care for and water the entire bed to keep all the living things in it thriving. It was a revelation to me, and my gardening efforts improved significantly when I put this new knowledge into practice.
Healthy soil is functioning soil. Functioning soil sustains biological diversity and microbial activity. It determines how productive and successful our efforts will be.
Healthy soil regulates the percolation of water, acts as a filter to buffer organic and inorganic materials, stores and cycles carbon, provides plant nutrients and keeps rooted plants stable and supported.
Did you know there are more living organisms in a teaspoon of healthy soil than there are people on earth? We have all had the experience of lifting a handful of rich, dark, humusy earth and feeling that it is indeed alive.
Our responsibility to keep it alive and thriving can be a little daunting, especially when half of the planet's soils are currently considered degraded. But protecting and improving soil health is really learning to protect and maintain suitable habitat for the soil food web.
What can you do? First, grow as many different species of plants as is practical in your garden. Look to nature for ideas on how to mix plants and take advantage of all the variety available.
Rotate annual vegetable and flower crops. Avoid planting vegetables from the same plant family (tomatoes and potatoes, for example) in the same spot each year. Rotating crops helps you avoid depleting some soil nutrients and also helps keep pests at bay by disrupting their reproductive cycles.
In Napa County, we are fortunate to have mild-enough winters that we can have something edible growing all year. If you have not yet attempted winter vegetable gardening, consider that growing vegetables in winter is good for your own health and for your soil.
When you are not growing vegetables, flowers or other plants, cover bare soil with cover crops or mulches. In winter, vegetation and mulches protect the ground from the effects of pounding rain, which can not only compact your soil but can also leach or wash away important nutrients. When soil aggregates remain intact, water, oxygen and nutrients can percolate down to nourish your soil, microorganisms and plants. Cover crops and mulches also provide habitat for those members of the soil food web that spend at least part of their time above ground.
One Natural Resources Conservation Service publication advises that if improving soil health is your goal, “you should not see the soil very often.”
In addition to keeping soil cool and moist, mulches such as compost, leaf mold or even straw (ideally, free of weed seeds) can also suppress weeds, especially early in the growing season. Your crops will have less competition when they are young and trying to get established.
To keep your soil healthy or to improve its tilth, disturb soil as little as possible and adopt no-till methods. Instead of uprooting spent plants, cut them at ground level and leave the root systems in the soil to decompose and create aeration paths and food for soil microorganisms.
If you are developing new beds or trying to revive tired, compacted soil, this is a great time of year to apply a few inches of compost or mulch. Perhaps visit the local bait shop for a container of live worms to introduce to your beds and let the winter rains begin your work for you.
Tilling or rototilling is traumatic for your soil. As far as the living organisms in your soil are concerned, the effect is the equivalent of an earthquake, hurricane, tornado and forest fire occurring simultaneously. Gently loosen soils with fork tools and avoiding turning and shoveling. These practices will go a long way toward maintaining the integrity of your soil.
Soil compaction can be a problem in winter. It happens when we walk on wet garden beds, especially when they are still recovering from rain. You have probably noted how hard paths get when walked on daily. Our local clay soil, inundated with water and then compacted by walking, driving, digging or tilling when the ground is wet, becomes hard as a brick. Fine for paths, not the best for growing vegetables and flowers.
Next workshop: “Sustainable Vegetable Growing” (Four-Part Series) on Sundays February 23, March 1, March 8 and March 15, from 2 p.m. to 4 p.m., at the University of California Cooperative Extension, 1710 Soscol Avenue, Napa. For more details & online registration go to Online registration (credit card only) or call 707-253-4221.
The UC Master Gardeners of Napa County are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website (http://napamg.ucanr.edu) or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.