When autumn arrives, several things can be done to prepare the garden for winter and the following growing season.
No Need to Clear-Cut the Perennial Garden
It is not necessary to clear-cut the perennial garden after the first freeze of the season. Leaving the leaves, stems, dried flowers, and seed heads of many perennials provides more interest through the winter months. Leaving the plant materials also provides an extra layer of protection for the crown and root system of the perennial. Plus, the dead stems and leaves collect fallen leaves, adding even more protection. Leaving the plant material in place and removing it in early spring instead of fall also helps provide food and protection to native pollinators, beneficial insects, and wildlife, such as birds.
While it is largely beneficial to leave the foliage in place through winter, removing plant material in the fall after it has naturally died back should be done for perennials with disease or insect pest issues during the summer. Additionally, those perennials that tend to be weedy or spread aggressively by seed benefit from late-season deadheading and clean-up to prevent them from being too weedy.
Consider a Blanket of Mulch
Leaving plant debris in place over the winter months can help shallow-rooted perennials that may frost heave. Frost heaving happens when the freeze-thaw cycle of the upper layer of soil works the crown and root system of the perennial plant out of the ground. If more protection is needed to prevent frost heaving, apply about four inches of mulch over the crown of the plant after the ground freezes, typically by late November in much of Iowa. Do not place the mulch on too early as it can slow plants from going dormant and make them more susceptible to damage from cold temperatures. Remove the excess mulch “blanket” in early spring as soon as the top layer thaws, typically around mid-March in much of Iowa.
Protect Marginally Hardy Perennials
Tender perennials can also be protected with cages placed around the plants and filled with straw or pine needles. Avoid using leaves as they tend to mat down over winter smothering the plants. As with extra mulch, place the protective layer late in the fall season and remove it in early spring. Do not use Styrofoam cones or domes as they can cause premature warming in the early spring bringing plants out of dormancy early and making them more susceptible to cold damage. Additionally, most plants will not fit under these cones without extensive pruning, and it is better to prune in spring rather than fall.
Good Clean-up is Important
Good fall clean-up is necessary in the vegetable garden removing all leaves, stems, fruit, and other plant parts after the first frost. Most edible plants grown in home vegetable gardens have serious disease and/or pest issues that can overwinter on plant debris, increasing its impact on crops in subsequent years. Removal and destruction of the diseased plant debris reduces the severity of many diseases in the next growing season. Removal of the plant debris also eliminates over-wintering sites for some insects and helps reduce insect populations.
Disposal of Debris
Composting the plant debris is a good option, assuming you have a compost pile that heats up to at least 140°F, which will kill most pathogens. Most home compost piles do not reach this temperature, but most municipal composting facilities do. Another option is burning, where legal.
Consider Tilling in Fall
Fall tillage provides several benefits. Fall is a good time to add amendments like well-rotted manure, leaves, compost, and disease-free garden waste. These amendments add organic matter and benefit the soil microorganisms and the overall soil health. Additionally, a fall-tilled garden dries out and warms up more quickly in spring, permitting earlier planting of cool-season crops.
Take Note of Where Each Vegetable Was Grown
Another way to prevent plant diseases next year is to take good notes in autumn of where in the garden each type of plant grew this year. Disease problems often increase when the same crop or crop in the same family is planted in the same area in successive years. For crop rotation to be effective, gardeners should not plant vegetables belonging to the same plant family in the same location for a minimum of three years. Selecting vegetable varieties that are resistant to specific diseases can also be helpful. Learn more about crop rotation in this article: Crop Rotation in the Vegetable Garden
Good Clean-up is Helpful
As with the vegetable garden, good fall clean-up is beneficial for containers and garden beds where annuals are grown to help prevent disease and pest issues and reduce unwanted reseeding of some annual species in future growing seasons.
Plant Cool-Season Annuals
Consider planting cool-season annuals to keep color and interest into the late fall season.
Decorate with Natural Materials for Interest Over Winter
Evergreen boughs, ornamental seed heads, decorative branches, and other materials can be arranged in annual beds, frost-proof containers, and window boxes to create interest all winter. Empty and store those containers that are not frost-proof to prevent cracking over winter.
Propagate Annuals Before Frost
By the end of the growing season, many of our annual plants in the garden are gorgeous to overgrowing! It is hard to watch these prized flowers die after the first frost. Fortunately, some annuals can be propagated from cuttings and brought indoors during the winter. This is a great way to extend their beauty inside and reduce the cost of annual flowers for next spring. Learn more about the process in this article: How to Propagate Annuals from Cuttings
Do Not Prune in Fall
While it may seem tempting, do not prune woody trees and shrubs in the fall. Pruning encourages new growth, and when done in the fall, the new growth that develops will not be well hardened off for winter leading to more potential for winter damage. The best time of year to prune is later winter and early spring (February through March in Iowa). Tender plants like roses or butterfly bushes will have dieback during the winter. During mild winters, that dieback will be less severe, so leaving all wood in place allows for more of the plant to potentially make it through the winter and for you to start with a larger plant the following spring. Wait until new growth begins to emerge in spring and prune these tender woody plants back to live tissue.
Learn more about all things pruning including tips, timing, tools, and techniques in this article: Your Complete Guide to Pruning Trees and Shrubs
Wrap Trunks of Young Trees
During the winter months, when food is scarce, rabbits and other rodents will chew and strip bark from woody plants. Protecting woody trees and shrubs, especially young plants, from browsing is important. Wrap young trees at least 36” up the trunk with tree wrap in late fall and remove the protection in spring. Adding tree wrap has the added benefit of protecting young trees from sun scald which can cause thin bark to split and crack on sunny winter days.
Install Fencing to Prevent Animal Damage
Place cages or stakes around young trees to prevent browsing and antler rubbing from deer. Stakes and fencing must be at least four feet tall to prevent antler rubbing. Cages around shrubs can also prevent damage from rabbits and rodents. Use rebar posts and 36” tall chicken wire pinned to the ground when needed. Make sure fencing is at least three feet tall, as animals can get over shorter fencing if there is deep snow cover.
Manage Fallen Leaves
A thick layer of leaves left on the lawn will damage and possibly destroy the turfgrass plants leaving behind patchy areas of dead grass that are unsightly and more prone to weeds. Leaves can be collected by raking, blowing, or using the collection bag on a mower and then removed from the lawn and added to a compost pile or sent to a composting facility. Gardeners can also manage leaves on the lawn by mowing. Chopping the leaves up with a mulching mower can help return organic matter to the soil, benefitting the lawn, and for most people, it is easier than raking and removing. The leaves must be chopped into pieces small enough to fall down between the blades of grass. When finished, very little leaf debris should be visible. Mowing is best done when the layer of leaves is thin and dry, so mow often throughout the fall. If the leaf layer is thick, mow over an area more than once.
Many Lawn Tasks are Best Done in the Fall
While we often think of fall as the time to start wrapping things up, many of the most important tasks for growing healthy lawns, like fertilization, seeding, and weed control, are best done in late summer and early fall.
Learn more about what you can do in the fall to promote healthy lawns in this article: Fall Tips to Ensure a Healthy Green Yard in the Spring
Fertilize the Lawn
Fall is also an excellent time to fertilize the lawn. Even though the turfgrass foliage stops growing in the late fall, the roots continue to absorb and utilize nutrients. An application of fertilizer in late October or early November helps promote root growth and early green-up the following spring. Apply 1 pound of actual nitrogen per 1,000 square feet. Learn more about fertilization in this article: Lawn Fertilization
Seeding the Lawn
Late summer/fall is the best time to start new lawns from seed. In Iowa, sow grass seed in late August through September. More information about seeding lawns can be found in this article: Seeding a New Lawn
Apply Weed Control
Fall is the best time for broadleaf weed control using herbicides. Applying herbicides in late September through early November allows the herbicide to be pulled into the root systems more effectively, especially if applied after the first frost of the fall. Learn more about weed control in home lawns in this article: Weed Control in Home Lawns
Aerate the Lawn
Aerification helps reduce compaction, thatch, and promotes better growth of the turfgrass. In Iowa, September or April are the best times to core aerate lawns in Iowa. Most lawns will only need aerification once a year. Learn more about aeration in this article: Core Aeration for Lawns
Bring Houseplants Back Indoors
Many of our houseplants enjoy a “summer vacation,” spending the warm summer months outside in a full or part-shade location. When nighttime temperatures start to dip consistently to around 50°F in the fall, it’s time to bring houseplants back indoors. In much of Iowa, this is typically in mid to late September.
Before bringing houseplants inside, check for insects. Once inside, keep plants isolated from other houseplants for 3 to 4 weeks. Typically, if there is going to be an issue with common indoor plant pests, it will be evident after about a month indoors. Inspect often and carefully and address any issues as soon as they are noticed.
The change in environmental conditions from outside to inside can be quite stark. Place plants brought back inside in bright indirect light. Provide supplemental light if conditions are too dim indoors. Learn more in this article: Moving Indoor Plants Outside for the Summer
Adjust Watering and Fertilizing Practices
Light for indoor plants reduces throughout the fall due to shorter days and the lower angle and intensity of the sun. This change in light conditions, along with the lower temperatures and humidity we see indoors going into the winter months, means houseplants are growing less. With less growth comes less need for fertilizer. Reduce fertilization frequency over the fall months. The change in light, humidity, temperature, and growth rate also means that watering needs may change. Check plants regularly, but only water when the soil is dry to the touch. Learn more in this article: How to Care for Houseplants
Pot Spring Bulbs for Forcing Indoors Over the Winter
Spring-flowering bulbs that can be forced indoors include tulips, daffodils, hyacinths, and crocuses. To enjoy spring-flowering bulbs in winter, gardeners must begin the forcing process in late summer or early fall.
Begin by partially filling the container (pot) with potting soil. Then place the bulbs on the soil surface. Adjust the soil level until the tops of the bulbs are even with or slightly below the rim of the container. Place additional potting soil around the bulbs. Allow the tops (noses of the bulbs) to stick above the potting soil. After potting, water each container thoroughly.
In order to bloom, spring-flowering bulbs must be exposed to temperatures of 40 to 45°F for 12 to 16 weeks. Possible storage sites include the refrigerator, root cellar, or an outdoor trench. During cold storage, water the bulbs regularly and keep them in complete darkness.
Once the cold requirement has been met, begin to remove the potted bulbs from cold storage. Remove pots from storage and place them in a cool (50 to 60°F) location that receives low to medium light. After 4 or 5 days, move the plants to a warmer (60 to 70°F) area that receives bright light. Keep the potting soil evenly moist during the forcing period. Flowering should occur in 3 to 4 weeks.
More detailed information on forcing spring bulbs can be found in this article: How to Force Spring-Flowering Bulbs Indoors
More information about other common tasks in the fall can be found at these links.