Fall Garden Care For Native Plants

By Laura Lovett, Gardening with Natives Committee Chair

Cooler temperatures are a cue to native gardeners to undertake fall garden projects. With modest effort now, we can keep plants healthy and attractive for the coming year. We may think of spring and summer as the growing season. However, in California, the arrival of consistent rain starts the growth cycle for many plants. Rather than being a dormant time, these native plants are putting on growth over the winter. Other plants take a needed rest until spring warmth returns. Gardeners can take advantage of these habits to tackle some essential fall chores.

Mulch. Mulch helps hold moisture in the soil, decomposes into useful nutrients and provides a home for insects that overwinter. Leave the accumulated leaf litter in place unless it is quite deep but keep it away from the base of tree trunks and crowns of plants. Shredded leaves, wood chips, bark products, and other organic mulches such as mushroom compost and grape seed mulch add nutrients and improve the soil structure as they decompose. If using purchased mulch, be sure it does not include invasive weeds and seeds. Avoid mulch from eucalyptus, bay and walnut as these plants are allelopathic—they produce chemicals that inhibit the germination of other species under their canopy.

Cut Back Grasses. Most grasses can be categorized as either cool-season or warm-season grasses. Cool-season grasses thrive in the cooler temperatures of spring and fall and begin growing in late winter to early spring. They will then flower and set seed in the spring to early summer, going dormant in summer. If you did not trim them down when they went dormant for fire safety reasons, now is the time to trim, rake or cut back grasses like California fescue, tufted hairgrass (Deschampsia sp.), melica and stipa sp., and deergrass. Deergrass can be cut back now, or as late as January just before it puts out new growth. Fall is ideal for dividing or planting cool season grasses either from seed or plugs.

Divide Plants. Dig up and divide iris and heucheras. Iris are ready for division when little pink or white roots appear at the edge of the fan of leaves. Soak the soil well before digging up and prepare to replant right away. It is important to keep the tubers and roots from drying out. Divide blue-eyed grass, hummingbird sage, Romneya, bleeding heart, wild ginger, sedges and rushes now also. Hold off dividing stream orchids (Epipactis sp.) until late December when they have died back to the ground and are clearly entering their winter dormancy.

Cut Down Milkweed. Asclepias or milkweed is the host plant for Monarch butterfly caterpillars. The caterpillars eat the milkweed after they hatch, ingesting the sticky sap that provides protection from prey. By fall, the adult Monarchs should be making their way to the coast to overwinter. If they find healthy milkweed plants in gardens, they may be tempted to lay eggs which will not survive, nor will the female make it through the winter. In order to encourage them to go into hibernation, all species of milkweed should be cut to the ground by early November.

Plant Cool Season Grasses and Wildflowers. If you are planning to fill in a patch of your garden with a wildflower seed mix, or a cool-season grass and flower mix, start the prep for it now. Once the area you want to plant is clear, soak it well and leave the weed seeds to germinate. Hoe these up and do a second round of soaking and hoeing if possible—the more the better.

The most common mistake people make when preparing to start from seed is that the soil they are sowing into is too loose and fluffy and the seeds drift down too far to grow to the surface. When preparing a seed bed, the soil medium needs to be densely packed so that the seeds, especially tiny ones, stay close to the surface. Mix the seeds with river sand (not playbox or beach sand, which contain salts) before spreading it. This allows you to see where you have sown the seed. Once sown, walk all over the space to make sure there is good seed-to-soil contact, then water in your seeds with a fine spray.

Hungry birds will be happy to help themselves to the food feast you have just spread. One option for protecting the seeds and new seedlings is to lay some light branches over the whole area. Alternatively, cover it with very light row-cover fabric pinned down with staples. Place some stakes or branches underneath to make sure the cover is up off the ground, so seedlings have room to sprout beneath it.

More tips: if using multiple single species and not a mix, spread each one in a drift rather than scattering them widely, and mark the drift with labeled irrigation flags. This will create clusters of color and make bees very happy to have so much nectar in one spot. Fill small 4” pots with starting mix, add a single species seed to the pot, label and water it. When these sprout, you will have a sample of what the early shoots and leaves look like for each species to guide you as you pull out the weeds that will also sprout. Keep the seeded area damp but not soggy.

Annuals were designed by nature to sprout and start growing quickly, so they will appear soon after planting. Perennials can be much trickier. Some wait years to germinate or need special conditions like charcoal, scaring of the seed coat, or long soaking to sprout. The best candidates to grow from seed are those that reseed once established, such as Blue Flax, Woolly Sunflower, Pearly Everlasting and Yarrow. For perennials that are trickier about conditions, starting them in small pots is probably the best way to control conditions and see what you have growing—or not.

Shrubs that produce berries often germinate best when the berries are very ripe. Soak the berries in water for about a week until they rot; then clean and plant. Coffeeberry and toyon both germinate successfully from seed.

Plant Bulbs. Fall is the perfect time to add native bulbs to your garden beds. Bulbs come up with the winter rains, flower in spring, then disappear in summer. They need this period of summer dryness and dormancy in order to complete their growth cycle. If watered during the summer, the combination of heat and water will kill many of them, so be sure to plant them with other species that get no summer water.

Plant in late fall, right after the first rain, placing each bulb 3-6” deep, root end pointing down. Shallow plantings often do not survive. Locate them in full or part sun. Do not amend the soil or locate them in extensively cultivated beds; they need to be undisturbed. You may need to label their location, so you don’t inadvertently plant something else in that spot. If gophers are a problem, protect the bulbs by planting them in cages; also guard against snails and slugs. New bulbs will have a hard time competing with well-established grasses. Grow them in containers for a year or two, following the same watering schedule as in-ground, until they are bigger and more established and can be planted out.

Prune. Sharpen your shears! For this major fall task, see handout on Pruning Tips for the Fall Garden.

All photos by Laura Lovett.