Do’s and don’ts for gardening after heavy rains

January brought a deluge of storms to Sonoma County, driven by a series of dramatic atmospheric rivers. As the month draws to a close, Santa Rosa has registered some 11 inches of rain for the month.

But that doesn’t tell the whole story. In the 23 days between Dec. 26 and Jan. 17, many areas of the county were hammered. Guerneville had 30.21 inches of rain, and nearly 24 inches fell in Cloverdale and Healdsburg.

All that water helped the region rebound from three years of drought, filling reservoirs but also flooding roads and fields and felling trees.

Heavy rains can raise a host of concerns for homeowners. The Sonoma County Master Gardeners have compiled a smart list of things we should and should not be doing in our still soggy landscapes, from watching out for certain critters to giving special care to flood- and water-damaged plants. They also have tips for checking trees for future risks. Falling trees can be dangerous, damage property and even prove deadly.

Mimi Enright, program coordinator for the Sonoma County Master Gardeners, said the blast of back-to-back atmospheric rivers and years of drought are a reminder of the need for better storm water management.

“We need to be thinking about how we manage our storm water more moving forward because of climate change,” she said. “We’re going to have periods of intense rainfall but we’re also going to have periods of intense drought.”

6 do’s

Do check for snails and slugs. These critters thrive in moist environments. You’ll often see them on sidewalks and driveways after it rains. Their feeding makes irregular holes on leaves and flowers, and they leave behind a slimy trail. Pesticide sprays and dusts are not effective under really wet conditions, so don’t bother using them. Instead, pick off the snails by hand or trap them with a wooden board trap (go to bit.ly/3we4msQ to see how).

Do remove weeds and unwanted plants. It’s much easier to pull weeds and remove unwanted plants when the ground is wet. Use this time to your advantage by catching up with any winter annual weeds like oxalis, nutsedge and groundsel. Be on the lookout for more in the coming weeks.

Do dump standing water. As the weather warms, areas with standing water become breeding zones for mosquitoes. This wet winter already favors a big mosquito season, so do your part to reduce mosquito habitat around your home. Dump out standing water in flowerpots, saucers, wheelbarrows and buckets, and clean clogged storm drains and gutters. Find more information at bit.ly/3D01Jie.

Do keep conserving water. During the fall and winter months, do what you can to use less water. Over-irrigating your plants during this time can lead to root rot and other waterborne pathogens. Turn off or adjust your irrigation schedule to reflect the increase in rainfall. You might buy a rain sensor for your sprinkler system to avoid irrigating while it’s raining.

Do be on the lookout for ants, cockroaches and earwigs. These pests may invite themselves into your home during flooding or heavy rains. Seal any cracks or openings in your house to block them from entering. Use weather stripping and door sweeps, and place sticky traps near entryways. Keep food tightly sealed and your environment clutter-free to prevent these pests from getting established indoors.

Do remove mushrooms. Wet weather encourages the growth of above-ground fruiting bodies of fungi. Mushrooms aren’t harmful to your garden or lawn, but you may want to remove them to prevent children and pets from eating them. See more information on mushrooms at bit.ly/3GSgPHO.

5 don’ts

Don’t fertilize your garden, lawn or outdoor potted plants. Any fertilizer you apply now likely will be washed off the ground or rapidly leached from the soil and into our waterways. Wait until the winter storms have passed and there is a stretch of time between days with rain.

Don’t use pesticides (sprays, dusts or drenches). Like fertilizers, these products are more likely to only contaminate waterways than control pests. Rainfall quickly washes away pesticides applied to foliage as sprays. Those applied to the soil as a systemic drench likely won’t be taken up by the plant in waterlogged soils. Instead, they’ll become runoff. Pesticide dusts need to stay dry to be effective, so now is not the time to use them outdoors, either.

Don’t prune plants. Unless you need to remove damaged limbs or branches after the recent windstorms, avoid pruning plants under wet conditions. Pruning at this time can make plants vulnerable to pathogens and easily spread disease from one plant to another. Apricot, cherry and olive trees should never be pruned during cool, wet conditions.

Don’t worry about tiny piles of soil. Earthworm activity increases in rainy weather, so if you see small piles of soil on top of landscape beds or the lawn, don’t worry — it’s just the earthworms coming out to get some air. As they do, they help aerate the soil. Earthworms deposit castings when they ingest soil and leaf tissue. When they emerge from the soil surface, they remove fecal matter. Castings are rich in nutrients and organic matter and benefit turf grass plants.

Don’t compact your soil. Avoid driving or excessive walking on soft ground, and keep heavy machinery off wet soils. Compacted soils make lawns, trees and shrubs more susceptible to disease, drought and insects by preventing oxygen and water from reaching plant roots.

Caring for flood- and water-damaged plants

• Remove any debris, such as mud and silt, that may have shifted and accumulated on your plants.
• If the soil is waterlogged, improve drainage by digging ditches or furrows to redirect water away from plants.
• Check the soil for compaction and loosen it with a garden fork. This helps improve drainage and makes it easier for water and nutrients to reach plant roots.
• To reduce additional compaction, wait until the soil dries out before you work with it. Avoid walking on waterlogged soil, which can cause compaction and more root damage. Stay off a boggy lawn!
• Inspect your plants for damage to roots, leaves and stems. Remove any damaged parts and prune back your plants to healthy growth, if necessary.
• Remove contaminated material. Assume any garden produce touched by floodwaters may be contaminated, and discard it. While the risk of contamination is low in residential areas, runoff from septic systems, pastures or industrial areas can carry potentially harmful microbes and chemicals.
• Closely monitor your plants for signs of stress, such as wilting or discoloration. Address any issues as soon as possible.
• Once dry, start to water your plants gently and gradually to help them acclimate to the new soil conditions.

Precautions for flooded gardens

• Discard any produce touched by floodwaters above or below ground.
• Wash and sanitize any produce that was in the ground during the flood but was left untouched.
• Wait at least 60 days before replanting.
• Wear gloves and closed-toe shoes, wash your hands thoroughly and mulch the garden and paths to control dust that may contain contaminants.

Did you lose a tree?

Trees still standing after rainstorms can be a hazard, especially if they’re at risk for falling. Here are signs your trees might have been weakened by storms and excessive rain.

Leaning: A recent change in a tree’s vertical axis or exposed roots around its base are signs the tree is in the process of falling and can fall over completely at any time. Take swift action to either correct the lean or remove the tree. Remember that some trees naturally do not grow vertically. If there hasn’t been a change in the angle of lean, this is not a problem.

Multiple trunks: As the trunks push away from each other, some become weakly attached and prone to splitting apart, causing them to fall. Inspect each trunk at its point of origin.

Weakly attached branches: Trees with many branches arising from the same point on the trunk tend to be weak and potentially hazardous. If one branch breaks, the others are more likely to fail. Inspect branches bigger than 3 inches in diameter at their point of attachment.

Cavities and other evidence of decay: Mushrooms and conks — bracket-like growths on tree bark or exposed roots — indicate root rot or wood decay. As the decay progresses, the wood weakens and failure is more likely. The location and size of these defects is important. Cavities or decay at the point where branches meet or at the base of the trunk are a concern. If the defect is large and at one of these structural spots, the tree is more likely to fail.

Trunk and branch cracks: Cracks confined to the bark are not usually a problem. Deeper cracks into the wood indicate the tree has become structurally weakened. If you see a crack greater than 3 inches deep, it likely extends into the wood.

Broken branches: Remove any broken branches that remain attached to the tree as soon as possible.

Dead wood: Branches that have died eventually will fall off, and the larger ones can cause damage. Remove any dead wood immediately.

Master Gardeners Helen Bates, Patricia Decker, Karen Felker, Clio Tarazi and Debbie Westrick contributed to this story. The UC Master Gardener Program of Sonoma County (sonomamg.ucanr.edu) provides environmentally sustainable, science-based horticultural information to Sonoma County home gardeners.