Many creatures in the garden go to sleep in the winter–but not your soil. As autumn leaves start to fall and our Northern Hemisphere tilts away from the sun, it comes time to say goodbye to many annual vegetable friends and prepare the rest of the garden for major soil building. Thanks to plentiful rainfall during the cool season, the soil reaps many benefits: many amendments are more easily distributed, the soil particles aggregate in more loamy ways, earthworms keep churning and building the soil profile, and microbes digest detritus into gold. So before going inside for wintertime, harness the natural processes outside to grow your garden’s capacity for an awesome season next year. Follow these nine steps:
1. Love Your Leaves
Fallen leaves from deciduous trees are one of the greatest and least expensive resources out there for building soil. Since leaves should be raked from the lawn anyway to keep it happy, your need for leaves is a win-win for you and your turfgrass! Bolster your stash from pesticide-free parks, neighbors’ yards, cemeteries and more. You can either generously spread leaves several inches deep over fallow vegetable plots and ornamental beds, or hoard them in compost bins to let them break down into leaf mold—a rich and dark black compost you’ll want to use everywhere. Just steer clear from mulching with black walnut (Juglans nigra) or Tree of Heaven (Ailanthus altissima) leaves around annual plants, as they are considered “allelopathic” meaning their chemical constituents may interfere with future plant growth.
2. Harvest and Tend
A little maintenance at this time of year goes a long way for disease prevention. Spend time in your vegetable garden and harvest all remaining warm season crops (corn, beans, tomatoes, squash, etc.), leaving only winter squash to cure on the vine if the weather is not too damp or close to freezing. Try your hand at saving seeds to plant next year, though be sure to do your homework first. Seed to Seed by Suzanne Ashworth is a great resource to get you started. Any pest-infested or diseased vegetable foliage should go in the curbside yard waste bin. Same goes for diseased foliage, branches or fruit on perennial edible ornamental plants, including roses and fruit trees. The sooner you get this material out of the garden, the less time the disease will have to multiply and return next year! This is especially important if you’re hoping to reduce codling moth and apple maggot populations.
Avoid most pruning at this time of year, as the moisture can increase the likelihood of fungal or bacterial infection. Also, pruning can inspire new growth -- with frost approaching it’s best to steer clear and reduce the possibility of cold damage. Still, it’s a good time to remove dead or broken branches to prevent further injury by wind. Leave your ornamental grasses, less-weedy perennial flower seed heads and stalks that are still standing. This will provide valuable food, forage and habitat for wildlife during the winter—especially overwintering native bees who like to nest in stems and grasses.
Lastly, if you have semi-hardy or tender potted plants be sure to move them to a protected place, ideally next to the house under an eave and out of the wind. If frost or near-freezing temperatures are expected, be sure to water the soil to help your plants weather the cold more successfully. Some containers may also be damaged by cold. If you are worried about expensive ceramic pots, wrap them in recycled bubble wrap or towels to protect from frost. Protect empty pots by moving them into a garage or storing them upside down and off the ground.
3. Tuck in Your Turf
Before first frost, mow one last time for the season, lower than usual (down to 1”). Spread a ¼” - ½” layer of compost over the lawn, raking it lightly in, and overseed any bare areas. Usually a grass seed mix consisting of mostly fescue works best in our area.
4. Weeds Be Gone
Bare soil in the fall makes for fertile weed breeding ground. Beat the weeds to it by mulching generously in your ornamental beds with arborist chips or leaves. In your vegetable beds, consider using leaves or pesticide-free straw. Another option is to “chop and drop” any non-diseased foliage that you remove from the garden, chopping it into 3-6” pieces with your pruners and using it as a mulch. Cover crop (see below) is another living option to outcompete many weeds in vegetable beds while building soil.
5. Sweeten the Soil
October is an ideal time to test your soil to get an accurate reading of nitrogen, phosphorus, potassium and other macronutrient levels, as well as acidity and organic matter. All this will help you determine what to do to help your garden grow the way you need it to next year. King Conservation District offers five free soil tests per lifetime to residents of King County. If heavy metals are a concern, contact the Garden Hotline and we’ll match you with a lab that fits your needs.
If you already know your soil needs lime to bring its pH closer to neutral, fall is a great time to add it. Cool season rains will help activate or dissolve it and change the soil pH in time for plant growth next spring. Likewise, if you already know your soil texture profile is too clayey or sandy and needs compost, autumn is a great time to add it and get the soil particles aggregating to become more loamy. Top-dress with compost and mulch over the top with leaves and/or burlap bags to keep down weeds.
To prepare the soil, or even sod, for future garden beds, try your hand at sheet mulching. Cover the desired area with cardboard or layers of newspaper, cover that with a layer of compost, and top it off with leaves and/or burlap as mulch. Over the winter, worms and soil microbes will break down the material into a bed of soil for you to plant directly into in the spring!
6. Grow Your Own Fertilizer
Cover crops are select plants grown in a vegetable garden to help build soil tilth, keep out weeds, reduce soil and nutrient erosion, and create nitrogen and organic matter to feed your soil and future plantings. Over the winter this is especially helpful, as some cover crops are hardy to freezing temperatures and are happy to grow when not much else can. In the spring, when about a third of the cover crop is starting to flower, chop it down into 2-3” pieces and either dig it into the soil or leave it on top as a mulch. A few examples of winter cover crops: cereal rye, crimson clover, field peas, vetch, fava beans and spelt.
As a general rule, hold off on fertilizing until spring. As many plants go dormant for the winter and slow down their growth in cool weather, they do not take up fertilizer as readily. This, plus rain, can make for high levels of macronutrients accumulating in important waterways like Puget Sound. Save your money and keep those nutrients where you need them by waiting until the weather warms up in April or May to apply fertilizer.
7. Protect Your Watering Supplies
Water plus frost means ice, so take time to store your watering system properly to keep them in working order next year. Disconnect and flush irrigation supplies before the cold sets. For drip irrigation, this means removing the main assembly pieces (timer, filter, blackflow preventer, etc.) to bring inside, and draining and coiling all ¼” lines, securing them at the ends of your garden beds. The larger lines can be kept intact. Automatic irrigation systems like those with sprinklers need to be blown out at this time of year by yourself or an irrigation professional. All other garden and soaker hoses can be drained and stored. In case of heavy frosts, consider covering spigots with old towels or Styrofoam caps.
8. Tune Up Your Tools
Don’t let your trusty tools get rusty over the winter! Keep them in proper shape for a big season next year by cleaning off the soil, sharpening them if necessary, oiling hand tools and pruners and storing them in a dry place. For wood-handled tools, wet a rag with linseed oil and give them a good wipe. Be sure to dry your oil-soaked rags out in the open and soak in water before disposal, as linseed oil can combust in a closed container or if wadded up in a ball. Some gardeners choose to clean off their metal-bladed tools in a bucket of sand moistened with linseed oil—a handy resource to have in your tool shed to keep your shovels sleek year-round!
9. Write it Down
It is so easy to forget what we do in the garden from year to year. If you grew vegetables, make a map of what you planted in which bed so that you know where to rotate plant families next year. Note any problems such as plant diseases, pests and failure to thrive as well as successes. Keep track of what plant varieties did well and which ones did not so that you can remember what you might want to grow again in the future. If you planted new perennials that die back to ground, mark them or note them on a map so that you remember where you put them, especially if they are something that slugs and snails might like next spring.
To learn more about soil building or winterizing, contact the Garden Hotline at (206) 633-0224 or visit us at www.gardenhotline.org. You can also find us on Facebook, Twitter, Pinterest and YouTube.