Gardens need rain, but too much rainfall can cross the line. Excessive downpours or extended periods of wetness can be harmful to garden and landscape plants.

Drought is such a common gardening threat that it gets a lot of attention. Far less attention is paid, though, to what happens when too much rain comes down. Plants that wash away or that rot in soggy soil are the most immediate and obvious problems. But a handful of more subtle, lingering, and long-term problems also can follow excess wetness.

Injured Plant Roots From Excess Rain

Too much water can damage or kill plant roots. Some plants can survive soggy soil for a short time, while others decline quickly.

Plants That Struggle in Wet Soil

These plants have very little tolerance for soggy conditions and may die after only a day or two of standing water:

• Lavender (Lavandula spp.)
• Wormwood or artemisia (Artemisia spp.)
• Lamb’s ears (Stachys byzantina)
• Carnations and other dianthus (Dianthus spp.)

These plants naturally prefer dry conditions and are more drought-tolerant than moisture-tolerant.

Plants That May Survive — But Still Suffer Damage

Some plants tolerate wet soil better, but their roots can still rot:

• Daylilies (Hemerocallis spp.)
• Many iris varieties (Iris spp.)
• Lilyturf and mondo grass (Liriope spp. and Ophiopogon spp.)

Even if the plant survives, root damage can weaken it and make it more vulnerable to:

• Extreme summer heat
• Winter cold
• Future drought stress

Damage May Take Time to Appear

Root injury is not always immediate. Plants may seem fine for weeks or months before symptoms appear.

Watch for:

• Browning leaves or needles
• Slow or weak growth
• Sudden decline later in the season
• Branch dieback

The long-term outcome depends on:

• The type of plant
• How long the roots stayed waterlogged
• Weather conditions during recovery

Evergreens Are Especially Vulnerable

Most needled evergreens are highly sensitive to saturated soil. However, they often stay green long after roots are damaged.

Like a cut Christmas tree that stays green indoors for weeks, an evergreen may not show signs of decline until months after the root system has been injured.

The most obvious and short-term effect of too much rain is the rotting of plant roots in soggy soil. George Weigel

What to do:

There’s not much gardeners can do about partial root damage, so follow these steps to avoid soggy root damage:

• Select plants tolerant of wet conditions in wet areas.
• Improve drainage by working compost into the soil at planting time, or creating raised beds.
• Avoid walking on soggy garden soil (that compacts it and makes it even more prone to future flooding).
• Remove excess mulch from around plant stems and tree trunks after the soil drains (2” to 3” is optimal), and keep the soil moist during ensuing dry spells.

Plant Disease Problems After Heavy Rain

Too much rain creates the perfect environment for fungal diseases. Warm, wet conditions can cause:

• Leaf spotting and streaking
• Browning or yellowing leaves
• Premature leaf drop
• Wilted or collapsed plants

The good news: many plants recover on their own, even if they look unhealthy for a while.

Don’t Assume the Plant Is Dead

Trees, shrubs, and perennials may:

• Drop leaves early
• Turn yellow or brown
• Die back to the ground

In many cases, plants will send out new growth next spring. Wait before removing them.

Clean Up Diseased Leaves

To reduce problems next year:

1. Rake up fallen leaves and plant debris
2. Throw them in the trash — not the compost pile
3. Remove as much diseased material as possible

This helps eliminate fungal spores that can re-infect plants later.

When to Take Further Action

If damage seems severe or keeps spreading:

• Identify the specific disease
• Contact your local Cooperative Extension office for help
• Consider fungicides or other treatments if recommended

Not every disease requires treatment, but early diagnosis can prevent bigger problems.

Slime mold often grows in wet mulch. George Weigel

Lawn Molds and Mushrooms After Heavy Rain

Lawns usually recover well after flooding or extended wet weather, but excess moisture can trigger fungal growth and other problems.

Common Lawn Problems in Wet Conditions

Too much moisture may lead to:

• Rust diseases
• Mildew
• Other lawn fungi
• Mushrooms and mold growth

In most cases, these issues are cosmetic and do not require treatment unless the damage becomes severe.

Mushrooms and Slime Mold

Wet lawns and mulch beds often produce unusual growths after heavy rain.

Lawn Mushrooms

Many mushrooms that appear in lawns are harmless, but some can be poisonous.

Remove mushrooms if:

• You are unsure what type they are
• Pets may eat them
• Young children are nearby

Slime Mold

Mulched garden beds may develop slime mold, a blob-like growth that:

• Starts yellow or orange
• Turns black over time

Slime mold is harmless to people and pets. If desired, it can simply be raked away.

Yellow Leaves After Excess Rain

Yellowing leaves are not always caused by disease. In many cases, plants temporarily lose access to nutrients after prolonged wet weather.

Why Leaves Turn Yellow

Soggy soil reduces oxygen levels underground. This can suffocate beneficial microorganisms that help break down nutrients for plant roots.

As a result, plants may develop:

• Yellow leaves
• Pale or faded color
• Weak growth

How to Help Plants Recover

This problem often corrects itself as the soil dries out.

If plants stay pale after the rain ends, consider applying fertilizer — especially products containing:

• Nitrogen
• Iron

These nutrients are often the most effective at restoring healthy green growth.

Leaning Trees After Heavy Rain

A tree that suddenly starts leaning after storms or flooding can be a serious safety hazard.

Why Trees Lean

Excess rain can weaken root systems by:

• Rotting roots in saturated soil
• Softening the ground around the tree
• Adding extra weight from wet leaves and wind

When roots lose support, the tree may begin to tilt.

What to Do

For Large Trees

• Contact a certified arborist or tree professional immediately
• Stay away from the tree until it is inspected
• Leaning trees can fall without warning

For Small Trees

Small, non-hazardous trees may be saved by:

1. Gently pushing the tree upright
2. Staking it securely
3. Leaving supports in place for up to one year

Soil Erosion and Soil Movement

Heavy rain and flooding can wash soil and mulch away from where they belong.

Watch for Exposed Roots

Erosion may uncover tree and shrub roots. Exposed roots can quickly dry out and die.

If you notice exposed roots:

• Cover them with soil or mulch as soon as possible
• Replace any washed-away material if needed

Watch for Soil Piling Up

Floodwater and runoff can also move soil and mulch into harmful locations.

This becomes a problem when soil or mulch piles up:

• Against tree trunks
• Deeply over root systems

Why Excess Mulch or Soil Is Dangerous

Too much material around roots can reduce oxygen levels and damage plants.

Potential problems include:

• Rotting bark on trunks
• Suffocated roots
• Decline caused by roots being buried too deeply

Adding more than 3 inches of soil or mulch over roots can create the same problems as planting a tree too deep.

Moderate the force of water running out down spouts by installing a stone bed or a splash block at the base. George Weigel

Lessons learned:

Heavy rains give good clues to help you make changes and avoid trouble in the future.

• Look for depressions where water stood for days and level it out with additional soil.
• Look where excess, unwanted water flowed, and correct it by adding drain pipes, dry streambeds, or swales to redirect it to a more desirable area.
• Consider adding a rain garden to capture and drain runoff instead of letting it wash away. These can be most attractive and environmentally friendly.
• For downspouts that blew soil or mulch out into the yard, mitigate the force by adding a bed of stones or a splash block at the bottom.
• For areas with poor drainage, make note to build raised beds before planting there or plant only plants that can withstand periodic “wet feet”.