Most people think about planting spring-flowering bulbs in the fall, but
often don’t think of planting the rest of the garden. There's more to plant in
fall than bulbs
– you can plant many perennials, grasses, trees and shrubs, and even some
annuals or vegetables in early fall! The fall planting season generally runs
from the beginning of August until the ground freezes.
Early fall is a great time to put plants in the garden. Air temperatures are cooler, reducing the stress on the plants, while soil temperatures are still warm, promoting root growth. The plant has plenty of time to build a healthy root system without having to also grow new leaves and flowers. Roots will continue growing until the ground is completely frozen. You just have to sure to plant in time to give those roots enough time to really get established before the ground freezes. Rainfall may be more abundant at this time of year and generally there are fewer insect and disease problems.
You can also stretch your gardening budget with fall planting. Many nurseries and garden centers offer good sales to reduce their inventory before winter. As long as the plants have been well cared for during the summer these are just as good as the ones you'd buy in the spring. Be sure to inspect the roots of these sale plants to make sure they're healthy.
Fall planting requires no more special preparation than any other time of year, but soil preparation is still important. Dig in compost and any elements recommended in your soil test report before planting. (If you have not done a soil test, do it before preparing the soil.) Mulch to suppress weeds, keep the soil moist and help prevent frost heaving. Add mulch for moisture retention and weed control after planting. For winter protection, wait until the ground freezes to place the mulch over the plants. Keep watering the new plants until the ground freezes, unless rainfall is adequate.
Spring-flowering bulbs must be planted in the fall because they need a period
of chilling in order to bloom. Tulips, daffodils, hyacinths and crocus are
popular and commonly available, but don't forget some of the "minor"
bulbs such as Chionodoxa (glory of the snow), Galanthus (snowdrops),
Muscari (grape hyacinth), and Scilla (including Siberian squill
and wood hyacinths). [See Bulb.com
for more information on planting and much more.] Fall is also the time to
fertilize and divide bulbs.
The fall is an ideal time to plant new perennials, as well as divide and
transplant those that are overgrown or need to be moved. Many plants
actually perform better when planted in the fall, especially spring blooming
perennials. Peonies, all of the true lilies, like Asiatic and Oriental
hybrids, garden phlox, coral bells (Heuchera) and poppies should be
divided in the fall.
Now is the time to give container-grown perennials a permanent spot in the garden. You can also add instant color to flowerbeds with chrysanthemums that are readily available in bloom this time of year. Be sure to select a spot where they will receive full sunlight and space them 12 to 14 inches apart.
Fall is the best time to reseed cool-season lawns in our area. Lawns sown in the
fall do better because as they grow quickly in the warm soil and cool air, but
they don't have to compete with the coarse annual weed grasses which only
germinate in spring and summer. The perennial grasses in a high-quality turf
seed mix have a chance to really get established. In the spring the thick growth
will shade weeds seeds enough to reduce or prevent germination.
As the weather turns cooler, cool-season flowers start to come on strong.
Replace spent summer annuals with traditional fall plants such as pansies and
ornamental cabbage and kale. Other annuals that will continue going even after a
light frost include snapdragons (I've even had these survive the winter in my
yard to bloom the following spring), petunias, and alyssum.
Pansies are normally grown as annuals, but they're really biennials or perennials. They will reseed themselves and may even survive Wisconsin winters to bloom a second year if protected by consistent snow cover or mulch. Plants that survive should be in good bloom by mid-May and continue into mid-summer. Fall plantings in University of Minnesota trials generally have been more uniform in growth and bloom, have had slightly smaller plant sizes, and have had slightly larger flowers than spring planted ones. Pansies are becoming more popular, and transplants are now available in some garden centers (Home Depot had them in Madison recently).
Most deciduous trees and shrubs can be planted in the fall. (There are a few
exceptions: birch, willow and swamp red maple trees are not good candidates for
fall planting because they do not produce any root growth this time of year.) As
these woody plants begin to go dormant, their roots are still growing vigorously
and plants can quickly get established under the ideal growing conditions of
fall. Plant before mid-October, however, to allow roots time to
re-establish before cold weather.
Fall planting of evergreens is more of a risk because they lose moisture from the leaves and needles they hold through the winter. You may want to delay the planting of evergreens until spring.
Add three to four inches of mulch over the roots to help keep the soil from drying out and to prevent large changes in temperature. Watering fall-planted trees and shrubs during dry periods will greatly increase winter survival.
Just like with annuals, the cooler temperatures of fall are great for cool
season crops such as broccoli, cabbage, lettuce, spinach and Swiss chard, and
root crops like kohlrabi, radish, turnips, beets and carrots. The flavor of
fall-grown vegetables is often better than spring-grown ones because they won't
bolt and become bitter in the cool temperatures. 
Check the seed package for the
number of days to maturity to determine when to plant so you will be able to
harvest your vegetables before the weather gets too cold. Or, use season
extenders such as floating row covers or cold frames to keep the plants growing
late into the season.
Garlic generally produces best when planted in the fall fro harvest the following year. Trials at the University of Saskatchewan showed yield of fall planted garlic doubles that of a spring planted crop! Garlic can be planted any time between late August and early October, but earlier is better. To plant garlic, separate garlic bulbs into individual cloves and plant the biggest cloves. The larger the clove planted the larger the resulting plant and bulb will be. Place the cloves about 3 inches apart at a depth of 2-4 inches. Winter protection, such as a minimum of 6 inches of snow or straw mulch may be used to enhance survival.
If you don't plan to put in a fall crop of vegetables, you might try plating a cover crop, or green manure crop, to jumpstart your garden next spring. Cover crops are sown in planting beds and tilled into the soil to add nutrients. See Cover Crop Fundamentals, an Ohio State University Extension Fact Sheet, for more on what and how to plant cover crops.
– Susan Mahr, University of Wisconsin
