In Iowa, spring weather is often erratic. Below-freezing temperatures in April and May can follow unseasonably warm weather in late March and early April. The cold spring temperatures can affect plants in gardens and home landscapes. The good news is that cold temperatures shouldn't affect most plants in the long term.
How to manage cold temperatures and the damage they can cause to trees, shrubs, fruit trees, spring bulbs, perennials, vegetables, and other plants is provided below.
Fruit Trees | Small Fruit | Trees & Shrubs | Conifers | Perennials & Spring Bulbs | Vegetables | Annuals | Lawns | Additional Resources
Fruit Trees
Freezing temperatures do not harm dormant plants, but they can damage new spring growth, especially flowers. As flower buds swell, they become increasingly vulnerable, with the greatest susceptibility just before, during, and after bloom. The extent of damage depends on the plant species, stage of development, and how cold it gets.
Colder temperatures, longer cold spells, and more advanced blooms increase the likelihood of frost or freeze injury. If flowers are damaged, this year’s fruit crop may be reduced, though the trees themselves are unlikely to be seriously harmed.
There are no practical ways for home gardeners to prevent freeze damage on fruit trees. While commercial growers may use wind machines or irrigation for frost protection, these methods are not feasible for home landscapes. Trees are too large to cover or mulch, and applying fertilizer or extra irrigation will not help. The best approach is to wait and see how the tree responds and then provide good, consistent care afterward to minimize additional stress.
Species Affected
Apricots and peaches are more prone to damage from a spring freeze as they bloom earlier than apples and pears. Colder temperatures will cause more extensive damage. For example, at petal drop on apples, a temperature of 28°F will kill approximately 10% of the developing fruit, while a temperature of 25°F will kill approximately 90% of the developing fruit.
Details on the temperatures that cause damage to fruit trees at different stages of development can be found in this article from Michigan State University: Spring Freeze Damage Thresholds for Tree Fruit (PDF).
Small Fruit
Strawberries
For best yields, strawberry plantings are mulched in the fall to protect plants from cold temperatures. Before flowers open (tight bud stage), buds can tolerate temperatures as low as 20°F; once blossoms are open, damage occurs at about 30°F.
If plantings are uncovered too early in March, flower buds are likely to be damaged or killed, resulting in reduced summer yields. Plantings protected with a straw mulch experience far less flower bud loss.
Raspberries
Yields of summer-bearing red, purple, and black raspberries may be reduced by below-freezing temperatures in April or May. Cold injury can cause stem dieback, reducing flower formation.
Although flowers usually open after the risk of frost has passed, open blooms can be damaged by temperatures just below freezing in the odd year of a late freeze.
Fall-bearing raspberries pruned to the ground in late winter are not affected, as they fruit on the current year’s growth.
Grapes
Grapes are vulnerable to late spring frosts once buds or shoots begin to develop. Swollen buds can be damaged below 26°F; plants at bud burst are injured at about 28°F. When one leaf has emerged, damage occurs at 28–29°F, and with two unfolded leaves, injury occurs at 29–32°F.
Cold-damaged buds or shoots may recover, but if temperatures are low enough, they can be killed. When an entire shoot dies, secondary shoots usually emerge from its base within 10–14 days. Because grape flowers form on new growth, freeze events rarely reduce fruit production, though fruit set may be delayed if new shoots must replace damaged ones.
Blueberries
Freezing temperatures can damage new emerging growth on blueberries. After a frost or freeze event, inspect stems for injury. After shrubs leaf out, remove any dead stems.
Flowers can also be damaged. For blueberries, damage is seen at 15–20°F at bud swell; 18–23°F when flower clusters are still tight; 25–26°F when flowers are still closed but full-size; and 27°F for open blossoms.
Gooseberries & Currants
Gooseberries and currants are cold-hardy plants, but the early growth and developing flowers can be damaged when temperatures drop below 28-32°F. New leaves and stems will grow to replace those damaged by freezing temperatures. Fruit set will likely be reduced if flowers are present during a freezing event.
Woody Trees & Shrubs
The extent of plant damage is dependent on several factors. These factors include temperature, plant species, exposure, and stage of plant growth.
Damage to Flowers & Flower Buds
Cold temperatures most noticeably affect early‑blooming trees and shrubs, such as magnolias and forsythias. Freezing conditions can destroy open flowers, turning them brown, limp, and mushy. Early spring cold can also damage or kill unopened buds on later‑blooming woody plants like crabapples and lilacs.
When flowers or buds are damaged, plants may bloom poorly or not at all that season, but their long‑term health is not affected. While the loss of blooms is disappointing, normal flowering should return next year if severe cold does not recur.
There are no practical ways for home gardeners to prevent freeze damage: trees and shrubs are too large to cover or mulch, and fertilizer or extra irrigation will not help. The best approach is to wait and observe how plants respond, then provide consistent, good care afterward to reduce additional stress.
Species Impacted
Because they bloom early, species such as magnolia, forsythia, rhododendrons, and azaleas often lose flowers during late‑season frosts and freezes. When temperatures drop well below freezing (28-26°F), or buds are close to opening, late spring frosts or freezes can also damage flower buds on crabapple, ornamental cherry, and lilac.
In contrast, some species, such as cornelian cherry dogwood and vernal witch hazel, are very hardy, and their flowers often survive even when covered with snow or ice.
Cold Temperatures Can Damage Newly Emerged Leaves
Newly emerged foliage is highly vulnerable to freezing temperatures. Freeze damage (below 32°F) can cause leaves to shrivel, turn brown or black, become limp, and eventually drop.
Home gardeners can’t prevent freeze damage to foliage, but most trees and shrubs rebound within weeks by producing new growth. Healthy, established plants are rarely seriously affected. Proper care, especially watering during dry periods, helps recovery, particularly for trees and shrubs planted within the last 3–5 years. In rare cases, branch tips may die; prune them only after they are confirmed dry and brittle. Fertilizer is not recommended for recovery from cold damage.
Species Impacted
Damage appears to be most severe on Japanese maple (Acer palmatum), northern catalpa (Catalpa speciosa), hackberry (Celtis occidentalis), katsuratree (Cercidiphyllum japonicum), yellowwood (Cladrastis kentukea), smokebush (Cotinus spp.) ginkgo (Ginkgo biloba), hydrangeas (Hydrangea spp.), magnolias (Magnolia spp.), oaks (Quercus spp.), and black locust (Robinia pseudoacacia).
On the other hand, most maples (Acer spp.), birches (Betula spp.), green ash (Fraxinus pennsylvanica), honeylocust (Gleditsia triacanthos), lilacs (Syringa spp.), lindens (Tilia spp.), and viburnums (Viburnum spp.) often experience little or no damage.
Conifers & Evergreens
Cold damage to conifers and evergreens is rare and usually occurs only when late April or early May freezes occur, as new growth is forming. When injury happens, it affects only the newly emerging shoots.
Symptoms include curling, wilting, and dieback of new shoot tips, sometimes only on the windward side. Damage typically appears immediately but can develop later as browning and wilting of new growth. Cold injury is often mistaken for herbicide drift, but herbicides damage older growth and new tissue.
Damaged shoot tips often die, though death may not be obvious for 2–3 weeks. Repeated frost injury over several years can cause plants to become stunted or bushy. While plants are not killed by shoot tip loss, they may appear misshapen as new shoots replace lost branch tips by late June or July. Dead shoots may persist until late fall or the following spring and can be pruned back to a live bud or side branch.
Perennials and Spring Bulbs
Spring Bulbs (Tulips, Daffodils, etc.)
Tulips, daffodils, and other spring‑flowering bulbs typically emerge in Iowa in March or early April, though mild winters can trigger early growth, most often on the south and west sides of buildings where reflected sunlight and warm soil increase temperatures.
While early foliage is undesirable, it rarely requires protection. Tulip and daffodil foliage is cold‑tolerant, and if winter conditions return, growth simply slows. Snow cover provides especially effective insulation from extreme cold.
Cold damage is more likely later in spring when plants are fully emerged and in bud or bloom. Flowers can tolerate light freezes (32-28°F) and light snow, but temperatures below 25-28°F may damage or destroy blooms on early varieties. Fully emerged foliage may also be injured, turning white and collapsing.
No immediate action is needed after cold damage. Leave foliage intact until it turns completely brown so the remaining healthy tissue can store energy for next year’s bloom. Even if foliage is damaged, plants may still flower if buds are unharmed.
Perennials
Most newly emerged perennial growth tolerates light freezes (28-32°F), including early‑emerging plants like bleeding heart, daylily, catmint, and columbine. In most cases, early leaf growth is unharmed by cold, but freeze damage can occur if temperatures drop below 25-28°F, causing leaves to turn white or brown or to collapse.
Damage severity depends on temperature, plant species, exposure duration, and growth stage. Unseasonably warm early‑spring weather can promote lush growth in perennials such as hostas, ferns, astilbes, and pig squeak, making them more vulnerable to cold injury. Perennials planted within the last year face the greatest risk of serious damage.
Most established perennials recover from freeze injury. Lightly damaged plants continue growing, and injury is often hidden by new growth or can be trimmed out. Severely damaged plants typically send up new growth from roots and crowns within weeks, though they may remain smaller than usual during summer. Good care, such as weekly watering during dry periods in spring and summer, supports recovery.
Vegetables
Perennial Vegetables
Asparagus
Asparagus may be distorted or curled when exposed to temperatures between 28 and 32°F, but it is still edible. When temperatures dip below 28°F, spears can be severely damaged or destroyed by cold temperatures, and should be cut off and discarded. New spears will emerge to replace lost ones, but yields may be smaller this year.
Rhubarb
Temperatures between 28 and 32°F usually cause little or no damage. A hard freeze (below 28nd 32°F) is typically required to cause serious damage. Rhubarb damaged by freezing temperatures will have black, shriveled leaves and soft, limp leaf stalks. After freezing temperatures, some gardeners are concerned about rhubarb's edibility. It's safe to harvest rhubarb if the plants show no signs of damage 2 or 3 days after the freeze event. Damaged rhubarb (blackened foliage and limp stalks) should be pulled and discarded. New stalks that emerge after the freeze are safe to harvest.
Cool Season Vegetables
Cool-season vegetables will tolerate temperatures below freezing down to 28-26°F with little or no damage. Very hardy cool-season vegetables like spinach, beets, collards, kale, carrots, cabbage, and Brussels sprouts typically sustain only minor damage (if any) when temperatures drop below 28-26°F and easily recover. Other cool-season crops, such as radish, lettuce, chard, and onion, will sustain minor damage when temperatures drop below freezing (32°F) but will readily recover within 7 to 14 days.
Any plants that see significant damage or death will need to be replanted.
Cold Temperatures Can Cause Poor Head Development on Broccoli and Cauliflower
Broccoli and cauliflower that survive cold temperatures often need to be replaced, even if the damage is not extensive, because they are unlikely to form usable heads. Exposure to prolonged cold temperatures below 50°F causes broccoli, and cauliflower plants to form heads prematurely (referred to as "buttoning"). Plants that button do not form usable heads.
Warm-Season Vegetables
Potatoes
Freezing temperatures (below 32°F) will damage potato shoots. Symptoms may vary from blackening of the leaf margins (minor damage) to death of all aboveground growth (severe damage). Fortunately, severely damaged potatoes will send up new growth within 10 to 14 days. There is no need to replant the potatoes.
Other Warm-Season Vegetables
Warm‑season vegetable transplants, such as tomatoes and peppers, and seeds of crops like green beans should not be planted until frost danger has passed. These plants do not tolerate freezing temperatures (below 32°F) and can be damaged by frost, which may occur at temperatures below 36°F. Properly hardened vegetables are better adapted to cool conditions and more likely to survive a frost or light freeze with only minor damage.
Cold‑damaged plants may develop brown or black leaves or leaf edges, wilt, become limp and collapse, or die. Plants with minor damage typically recover within a few weeks, but warm‑season vegetables with significant damage should be replanted.
Annuals
Be Sure to Harden Annuals Before Placing Them Outside
Any annuals planted outdoors should be properly hardened to acclimate them to cooler temperatures. Those hardened annuals are more likely to survive a frost or a light freeze with little to no damage than those that are not hardened.
Frost Damage & How to Manage It
Damage to annuals from cold temperatures includes brown or black leaves or leaf edges, portions of the leaves turning white, wilting, tip die-back, plant collapse, and death.
Annual transplants set out before the danger of frost has passed in the first part of May are likely to be damaged by frost or freezing temperatures. Impatiens, petunias, marigolds, wax begonias, and other warm-season annuals that have suffered significant damage will need to be replanted. Those with light damage (brown leaf edges) should recover in 7 to 14 days.
Cool Season Annuals are Less Likely to Be Damaged
Cool-season annuals are plants that prefer cool temperatures and grow best in spring or fall. They include species like pansy, sweet alyssum, snapdragons, ornamental cabbage, and many others. These species tolerate a light frost, often surviving down to 28°F or sometimes even 25°F with little damage to flowers or leaves. Most cool-season annuals will see no damage during a late-season frost or freeze, and those that do see light damage will recover over the next 7 to 14 days. Plants that suffer significant damage will need to be replanted.
Lawns & Turfgrass
Cool-season turf grown across Iowa, including Kentucky bluegrass, perennial ryegrass, and fescues, is very tolerant of cold temperatures. After a frost or freeze, the turf may temporarily stop growing, but little or no damage will occur. Growth will resume with the return of warmer temperatures.
Related Information
- Frost Dates in Iowa
- How to Protect Plants from Frost and Freeze
- Protecting Trees and Shrubs in Winter
- How to Care for Newly Planted Trees through Winter
- Winter Damage on Trees
- How to Prevent Ice and Snow Damage on Trees and Shrubs
- Using Deicing Salts in the Home Landscape
- Overwintering Unplanted Trees, Shrubs and Perennials