We’ve had just about every kind of weather imaginable in recent weeks – from record-breaking highs to bone-chilling lows, hail storms, snow showers, thunder and drenching rain. There’s not much we can do about the weather, but many gardeners wonder if there is something they can do to help their plants – especially spring-flowering ornamental trees and shrubs and fruit trees.

In general, the further along flowers are in their development, the more susceptible they are to freeze injury. Many flower buds are at risk of injury when temperatures drop down to 30 degrees F. or below. The amount of injury depends on just how cold it gets, how long it stays that cold and how open the flower buds are. It is not unusual for subfreezing temperatures to occur as late as early May in Pacific and Grays Harbor counties. Many gardeners hold off setting out tender bedding plants until after Mother’s Day to avoid potential frost damage.

Home gardeners can minimize plant damage from cold temperatures by simply covering small plantings with plastic tarps or blankets. Although they provide a limited amount of protection at sub-freezing temperatures, even a degree or two can make a difference. In addition to covering tender plants with a protective covering, turning on the sprinklers will also prevent cold injury to plant foliage and blossoms.

This is how it works. When water changes from a liquid to a solid state (ice), a tremendous amount of energy is released. This energy is called the “heat of fusion” and is equal to 1200 BTUs per gallon. Sprinkling when air temperatures are below or approaching 32 degrees F. is sometimes called “icing” and utilizes the heat of fusion to provide cold protection for plants. Heat is released as long as water is freezing. This prevents plant temperatures from dropping below 32 degrees F. It’s important to emphasize this fact because the temperature that plants freeze is usually below 32 degrees due to dissolved solutes in the plant sap.

The key to successful use of sprinkling is to apply enough water to cover the plant surface so ice forms and heat is being continuously released. The sprinklers should be turned on when the temperature drops to 32 degrees and left on until temperatures increase above 32 degrees. According to meteorologists, the coldest temperatures are usually reached in the morning just prior to daylight.

Do April showers bring May flowers? Unfortunately, the impact of April’s showers on May flowers isn’t always positive. Too much rain while the plants are blossoming and new leaves emerging provides an ideal environment for fungus diseases resulting in blighted flowers and premature leaf-drop. In fact, moisture is paramount for the development and rapid spread of some of our most common plant diseases including brown rot, blossom blight on cherries, apple scab, and dogwood anthracnose.

Gardeners can help minimize plant disease development through the application of protectant fungicides. Protectants are applied to healthy plants to prevent fungal spores from germinating or penetrating host tissue. They must be applied before the fungal spore has a chance to infect the plant. New plant tissue that develops after application is unprotected. Protectants are usually not effective once the fungus is within plant tissues. Examples of protectants include mancozeb, coppers and chlorothalonil.

Chlorothalonil – sold under the trade names of Bravo 500*, Daconil 2787*, Fung-onil*, and Ortho Multi-Purpose Fungicide* – is a good general-purpose fungicide registered for use on vegetables, fruit and many ornamentals including shade trees. It is one of the longer-lasting fungicides so you do not have to apply it as often.

Another option for those who prefer to use an organic fungicide is Sulfur, sold under the trade names of Safer’s Garden Fungicide*, Sulfur Plant Fungicide* and many other names with the word sulfur in them. It is active against powdery mildews, some rusts, leaf blights, and fruit rot. It is labeled for use on fruit, beans and many ornamentals.

Captan is one of the best all-around, general-purpose fungicides to control a huge variety of plant diseases, but is not very good against powdery mildews and rusts. It can be used as a spray, dust, and dip or seed treatment and is labeled for use on ornamentals, lawns, vegetables and fruit.

Triforine, commonly sold under the trade names of Funginex* and Rose Pride Funginex*, is a systemic fungicide used to control powdery mildew, rusts and some leaf spots or blights. It is labeled for use on ornamental plants.

* Sometimes it is necessary to use trade names for educational purposes. No promotion of specific products is implied or intended.