As nighttime temperatures cool and we pick the last of our summer crops, it is time to prepare the garden for winter and next spring. Many activities done now can make your late winter and spring gardening easier and your garden more beautiful and productive.
Cleaning up and mulching: These are important steps for vegetable beds. Remove tired summer vegetable plants and clean up debris and weeds to reduce insect, pest and weed issues in the spring. Insects can hide in plant parts and debris, and disease-causing fungi and bacteria can survive in the soil over the winter. Come spring, they emerge or become active and attack new plants or tender spring growth.
Once you've cleaned up, add a layer of clean mulch to beds and around perennial plants. Mulching can help prevent diseases and will feed your soil. It also retains soil warmth and moisture and protects soil from compacting during heavy rain. Mulching with organic materials, such as compost or wood chips, will feed soil microbes and fungi, improving soil structure and health.
If you use tree leaves for mulch, move them to an area with unrelated plants. For example, use oak leaves around fruit trees, shrubs, or flowers. This practice will help disrupt some disease and insect life cycles. For information on the pros and cons of various organic mulches, see “Improving Soil with Organic Mulches,” one of many Healthy Garden Tips available from UC Master Gardeners of Napa County.
Plant a cover crop: Now is a good time to sow a cover crop to improve and retain your soil. To add nutrients, use legumes such as clovers or beans. To improve soil structure, use deep-rooted plants such as mustards or radishes. To minimize erosion, use a combination of cover crops, including some grasses. Seed mixes can be found at local nurseries.
If planted now, your cover crop will grow through the winter. Cut it down a few weeks before your planned planting time in spring. If possible, leave the debris on the soil surface to break down, further benefiting the soil as a green manure and mulch.
Keeping soil covered with plants or mulch over the winter helps prevent erosion and improves water penetration. Living roots feed all the microbes, fungi, worms, and insects that live in our soil, keeping it healthy. Here's a good summary of California cover crops from Audubon California.
Fall pruning: Deadheading (removing dead blossoms) can encourage some plants to keep blooming into the fall and will make the garden look neater. You may want to leave some seedheads for visual interest and color and as a food source for birds. I usually leave Cosmos seedheads and enjoy watching tiny birds sway on them while eating the seeds. Cosmos do self-seed readily, but if they come up where I don't want them, I can always transplant them.
Fall is a good time to prune many winter-dormant plants and those that bloom in late spring through summer. Start by removing dead and diseased wood, stems, branches, and leaves. Put diseased trimmings in the municipal compost bins, not your home compost. The municipal composting process gets hot enough to kill diseases; your own compost pile likely does not.
Not all plants should be pruned in the fall. Some prefer pruning in spring or summer or not at all, so check references before doing major pruning. Last winter I failed to cut back my pineapple sage and shrubby perennials. They stayed green all winter but looked ugly by spring, and it was then too late to prune. Lesson learned.
Warm-season grasses grow and flower in warm weather and turn brown in winter. They can be trimmed back to 2 inches in fall or spring, although you may want to leave them alone if they have colorful seedheads that provide winter interest or attract birds. Cool-season grasses grow mainly in the spring and fall when temperatures are below 75?F. They stay green all summer but don't grow much in hot weather. Prune these grasses in early spring, but do not remove more than two-thirds.
For guidance on pruning ornamental shrubs and trees, one of my favorite references is American Horticulture Society Pruning & Training by Christopher Brickell and David Joyce. This book includes details about when and how to prune, along with clear diagrams and general information on techniques. For a guide to pruning California native plants, including native grasses, visit the Theodore Payne Foundation website. Look under “Fall Garden Guide” for details on maintenance and care.
For any pruning or gardening activities, be sure to wear good gloves, gauntlets, or sleeves to protect your hands and arms. Wear eye protection and make sure your tools are sharp. Clean all your tools after you use them to keep them sharp and ready for their next chore.
To learn more, attend the Napa County Master Gardeners “Fall Garden Clean-up” workshop on Saturday, October 6 (details below).
Workshop: Join UC Master Gardeners of Napa County for a workshop on “Fall Garden Clean-up” on Saturday, October 26, at Las Flores Learning Garden, 4300 Linda Vista Avenue, Napa. Learn how we put the various garden plots to bed for the winter. There will be hands-on activities so you can learn how to implement these techniques in your own garden. Register here.
Library Talk: Join UC Master Gardeners of Napa County for a talk on “How to Improve Water Retention in our Landscapes,” on Thursday, November 7, at 7 pm via Zoom. Learn some water catchment/retention approaches that you can use in your own yard to “Slow It, Spread It and Sink It.” Register to receive the Zoom link.
Help Desk: The Master Gardener Help Desk is available to answer your garden questions on Mondays and Fridays from 10 am until 1 pm at the University of California Cooperative Extension Office, 1710 Soscol Avenue, Suite 4, Napa. Or send your questions to mastergardeners@countyofnapa.org. Include your name, address, phone number and a brief description.