Photo credit: Steve Williams
Precipitation, manifested by rain, freezing rain, sleet or ice pellets, snowfall, and hail, is an environmental factor influencing plant growth. Water is essential to all life and it is needed for healthy plant development. Water enters a plant's stem and travels up to its leaves where photosynthesis takes place. Photosynthesis is the process by which plants manufacture food in the form of sugar. Without water plant cells become damaged and plants fail to grow as they become deprived of nutrients. Too much water, however, injures plants, compacts soil, and leads to erosion. Root loss occurs when excess water reduces oxygen in the soil. A plant cannot grow without healthy roots. Extreme summer rain can leach nitrogen out of the soil; nitrogen is vital for photosynthesis. Snow provides moisture and protects plants from fluctuations in temperature, but heavy snow can harm trees when its weight breaks branches. Ice, hail, and deicing salts injure plants. As a side effect, deicing salts potentially lead to storm water pollution.
Air temperature influences all plant growth processes including photosynthesis, respiration, transpiration, breaking of seed dormancy, and seed germination. A high temperature generally causes plants to mature early, but extreme heat will slow growth. Hot weather will cause your cool-season vegetables, such as lettuce, to bolt. An excessively low temperature affects plant development leading to some plants becoming dormant to enable them to withstand the cold. After dormancy, they may require a chilling period before resuming growth in spring. Wide fluctuations in temperature can damage plants, especially in winter. With alternate freezing and thawing of the soil, shallow-rooted plants are likely to heave. Too hot or too cold temperatures may impede fruit set on your tomatoes and other vegetables and affect their flavor. Most gardeners have seen the damage caused by an unexpected frost. An indirect effect of a warm winter may be more insects in spring.
Humidity is water vapor in the air not necessarily caused by precipitation. When relative humidity levels are too high, or there is a lack of air circulation, a plant cannot make water evaporate or draw nutrients from the soil. One effect is a fungal disease such as powdery mildew.
Wind is an essential aid in the pollination process of some plants and grasses. It can, however, also disperse pathogens and noxious chemicals. Wind dries out wet plants, preventing mildew-type diseases. There is a problem, however, if the plant cannot replace the water fast enough. An example is when the leaves or needles of evergreens dry out in winter and they cannot restore the lost water because the ground is frozen. Strong winds can topple trees and other plants.
Light is a climatic factor that also affects plant growth and development. It is essential in photosynthesis and other important plant processes. Summer days with excessive rainclouds that block sunlight prevent plants from getting the food they need to grow, reproduce and survive.
How to Minimize Harmful Weather Effects
- Select native plants. Native plants often fare best as they adapt to local conditions.
- Choose plants that are more resistant to fungal disease and pests. This information will be on the label.
- Choose a diversity of plants as a hedge against new insect pests that appear when their ranges expand.
- Maintain space around your plants to create good air circulation.
- Make sure the plants you buy are suitable for your USDA hardiness zone.
- Keep your plants healthy, from correct planting to watering and feeding, to help them deal with stress.
- Make wise choices when buying trees and shrubs. Don’t choose trees with inherent weak wood or shallow roots such as willows (Salix spp.) Willows are fast growing but weak-wooded trees very susceptible to damage in storms. They lose branches or even topple over when stressed by wind, ice or snow.
- Water evergreens well before the ground freezes. Apply an anti-transpirant to evergreen shrubs and small trees to prevent winter injury through water loss.
- Wrap young trees to protect them from fluctuating temperatures.
- Mulch your perennial beds to help safeguard them from seesawing temperatures. Mulch can reduce summer temperatures by 20°F. Add a layer of shredded bark or wood chips. After Christmas, I use the branches from my Christmas tree as mulch.
- Cover plants with fabric for protection when frost is forecast.
- Create some raised beds. I find that raised beds provide better drainage than conventional beds during heavy rainstorms.
- Amend your soil with organic material to help with drainage.
- Don’t shovel snow containing de-icing salts onto plants.
- If necessary, plant a windbreak of one or more rows of trees or shrubs to provide shelter from the wind and to protect soil from erosion.
- Create a rain garden, a planted depression that soaks up rainwater runoff.