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With the cooler weather, gardening tasks may be slowing down some, but there are still plenty of things to do in the garden and landscape in the fall and winter months. Here are a few things to think about as you head into the next planting season. Follow the list to reduce future pest problems and have healthier plants.

Cleaning up

• Pull out annual plants that have reached the end of their growing season, such as tomatoes, squashes, and peppers.
• Remove and clean up old fruit and nuts in and under trees to avoid harboring pests and diseases.
• Remove fallen leaves from beneath deciduous fruit trees and roses.
• After cleaning up, add leaves dropped during fall to a compost pile. Turn and keep the compost pile moist.
• Apply organic mulch where thin or soil is bare beneath trees and shrubs. See our website for more information about mulching. 

Pruning

• Prune deciduous trees and shrubs such as apple, crape myrtle, pear, rose, spirea, and stone fruits.
• Make cuts properly to encourage good form and structure.
• Remove dead, diseased, and borer-infested wood.
• Not all pests and host plants should be pruned in the fall. Certain pest-infested wood, such as damage from shothole borers, and plants such as apricot and cherry should be pruned during the summer. 

Planting

• Fall is a good time to plant bare root deciduous trees, shrubs, and vines, such as caneberries, fruit and nut trees, grapes, and roses.
• Plant California natives now so they can establish before the summer.
• When you add new plants to your garden, select species and cultivars that are well-adapted to the local site.

Adjusting irrigation

• The weather has turned wetter and cooler, so adjust watering schedules since plants won't need as much water.
• Check your irrigation systems for leaks and broken emitters and do any maintenance.
• You might want to upgrade the irrigation system to improve its water efficiency.
• If it's not raining, water plants as needed to keep root zones moist, but not soggy.
• Prepare for rainfall by improving drainage. The goal is to prevent water ponding around trunks and foundations.
• Install downspout diverters to direct runoff into landscape soils, but avoid waterlogging of soil.

Monitoring for pests

• Look for Asian citrus psyllid on your citrus trees and if you find it in a new location, report it to your local county agricultural commissioner.
• Also monitor for damage and pests such as brown rot, leafminer, root rots, and snails on citrus trees.
• Check for leaf curl or shot hole on apricot, nectarine, peach, and plum trees.

Lawn care

• All types of lawns are actively growing during the fall months. Fertilizer applied at this time will help ensure that turfgrass is vigorous enough to outcompete weeds and resist other potential pest problems. Visit our website for more information about correct fertilization of established lawns, including when to fertilize in your region.
• Practice weed management for annual cool-season weeds. It's also not too early to consider management for weeds that emerge in springtime.

For more information, see the Seasonal Landscape IPM Checklist.

[Original article published in the Fall 2021 issue of the Home & Garden Pest Newsletter]

 [From the UC IPM blog Pests in the Urban Landscape] 

Citrus trees need care throughout the year, including cultural practices to keep trees healthy and pest management. During the fall season, several pests can attack citrus trees in many California regions. 

Brown Rot

Monitor for this disease by checking for damaged fruit on your tree, as well as fruit in storage. Sometimes affected fruit develops a pungent odor and can ruin fruit held in storage. See the UC IPM web page on Brown Rot to learn more.

Citrus Leafminer

If you see what look like small “tunnels” on your citrus tree leaves, your tree might have citrus leafminer. The adult stage of this pest is a small, light colored moth; the larval stage feeds and develops inside the leaves of young citrus and other closely related plants.

Citrus leafminer rarely causes problems for mature trees, however, it can seriously damage very young trees. Read the UC IPM Pest Notes: Citrus Leafminer for recommendations for prevention or management.

Snails and Slugs

Snails and slugs are attracted to citrus trees and can feed on foliage and fruit. A good sign that these pests are the perpetrators of tree damage are the silvery trails of slime along the ground or on tree leaves, or even see the snails or slugs themselves. For management tips, read the UC IPM Pest Notes: Snails and Slugs.

Asian Citrus Psyllid and Huanglongbing

You may have heard of the Asian citrus psyllid (ACP) and the deadly disease huanglongbing (also called citrus greening) that has been featured in the news. This disease doesn't pose a threat to humans or animals, but is deadly to citrus trees. Once a tree develops huanglongbing, there is no cure, so for this disease prevention is key.

Stopping this serious citrus pest will require everyone's help. To learn more about the psyllid and the disease, as well as what you can do, visit the UC IPM Pest Notes: Asian Citrus Psyllid and Huanglongbing Disease.

UC IPM Web Site

For information on managing other citrus pests in the garden, see the UC IPM webpage on Pests in Gardens and Landscapes: Citrus.

The Autumn Equinox signals a time of change in the seasons. The weather becomes cooler, the days shorter, skies turn a softer blue with occasional clouds, summer vegetable gardens are finishing up, and deciduous trees change colors and drop their leaves. By mid-November our neighborhoods and gardens will be littered with fallen leaves.

People often rake their leaves and put them out to be picked up as trash. I have always preferred to leave the leaves for my garden.

If you take a walk in a forest, you'll see leaf layers several inches deep around trees and bushes. Fallen leaves have a complex relationship with trees and nature, providing many benefits which can be reproduced to some extent in our gardens.

Natural Mulch

Leaf litter prevents rainwater and wind from carrying the soil's nutrients away. Water trickling through the leaf layer carries essential nutrients such as carbon, phosphorus, nitrogen, and other inorganic compounds, thus replenishing the soil.

Fallen leaves have the same weed suppression and moisture retention properties of shredded wood mulch—and they're free! Where mulch is desired as a decorative element, what could be more seasonally appropriate than a pile of brightly colored fall leaves? This natural mulch also provides insulating winter cover from cold temperatures for roots, seeds, and bulbs.

A Web of Life in Leaf Litter

Leaf litter isn't just free fertilizer and mulch. It provides food and shelter for a wide variety of living things including spiders, snails, worms, beetles, millipedes, mites, toads, frogs and more—these in turn support mammals, birds, reptiles, and amphibians that rely on these creatures for food.

Detritivores (organisms that eat dead or decaying plants or animals) break up and excrete leaf litter. Fungi and bacteria then take over and complete the recycling process converting these smaller pieces into nutrients which then sustain neighboring plants. They in turn help support biodiversity by becoming food themselves.

Some creatures use leaf litter and other dead vegetation to insulate themselves from winter's chill, while others, such as earthworms, feed on the litter, breaking it into smaller pieces.

Numerous bird species such as robins and towhees forage in the leaf layer searching for insects and other invertebrates to eat. 

Raking up leaves and putting them in the trash could have the unintended consequence of removing some of next year's garden butterflies and moths, many of which are pollinators. Most butterflies and moths overwinter in the landscape as an egg, caterpillar, chrysalis, or adult. In all but the warmest climates, they often use leaf litter for winter cover. Fritillaries and wooly bear caterpillars will tuck themselves into a pile of leaves for protection from cold weather and predators. Some Hairstreaks lay their eggs on fallen oak leaves, which become the first food of the caterpillars when they emerge. Swallowtail butterflies disguise their cocoons and chrysalises as dried leaves, blending in with the “real” leaves.

Bumble bees also rely on leaf litter for protection. At the end of summer, mated queen bumble bees burrow an inch or two into the earth to hibernate for winter. An extra thick layer of leaves is welcome protection from the elements.

All of which makes leaf litter an integral part of a complex web of life.

What You Can Do

Leaving the leaves where they are is ideal but isn't always practical for gardeners. If you have lawn, you can mulch the leaves with your mower, rake them up, and place them back in the garden around trees, shrubs, and plants. Spreading some of the chopped leaves around on your lawn will also nourish it. If possible, leave some leaves undisturbed in planters since shredded leaves will not provide the same cover as leaving them whole, and you may be destroying eggs, caterpillars, chrysalis, and other micro-creatures along with the chopped leaves.

Composting leaves is a terrific way to recycle and create a nutrient-rich garden soil amendment at the same time. Some gardeners opt for shredding their fall leaves for use in compost piles. Like people who mulch their lawn leaves with a mower, consider leaving some leaves undisturbed in garden beds and lawn edges. If space allows, you could create a leaf pile, allowing it to break down naturally, or add the leaves gradually to your compost pile over time. Such efforts will keep leaf litter critters safe and allow you to benefit from the rich garden gift that falls from the trees above.

While it is ideal to “leave the leaves” permanently—for the benefits mentioned above—if you do decide you need to clean your garden and remove the leaves in spring, try to wait until later in the season, so as to give the critters that have been protected by fallen leaves over the winter time to emerge and depart.

Some gardeners may be concerned that autumn leaves, matted down by rain or snow, could have a negative impact on their perennials. However, a thick layer of leaves provides additional insulation against chilly weather and protects newly planted perennials from frost which could damage tender roots and shoots. Anyone who has spotted fragile spring seedlings popping up in the woods knows that all but the most fragile of plants will erupt through the leaf litter in spring without trouble.

So, leave the leaves. While you can't perfectly emulate a forest, your garden will be healthier and more diversified, you'll help support a vast array of wildlife, and you'll reduce the strain on landfills. 

Denise Godbout-Avant has been a UCCE Stanislaus County Master Gardener since July 2020.