Plant Palette

Plant Palette

Plants & the Weather

Photo of Jennifer Schultz Nelson

Jennifer Schultz Nelson
Extension Educator, Horticulture

The Master Gardener Help Desk at the Extension office is always busy this time of year. Calls come in year round, but spring and summer are always the busiest months. It's not unusual to see the same problem show up again and again depending on the time of year. For example, Japanese Beetle questions typically begin in late June, and Asian Lady Beetle questions usually start in the fall as the weather turns cool, and again in the early spring as the weather warms.

Some problems occur throughout the growing season and beyond. These can be tougher to pin down, and may have cumulative effects. Problems related to the weather fall into this category. The Help Desk receives numerous calls about plant problems that relate back to the weather. This year is no exception.

Clearly, controlling the weather is out of the question. But we can select plants that are well suited for a wide range of conditions, plant them properly, and keep them healthy.

Plant problems caused by weather conditions fall into the category of abiotic stress. Abiotic stress is defined as the negative impact of non-living factors on organisms in a specific environment.

The most common weather-related abiotic stressors include: extremely hot or cold temperatures, drought, flooding and high winds. Choice of plants and gardening practices can combat some of these stressors, but realize there are limitations. Listed below are some of the common problems resulting from extremes in the weather; there are others. If you have further questions, please don't hesitate to contact the Macon County Master Gardener Help Desk at (217) 877-6872.

  • Extreme Heat: Excessive heat, such as the extreme temperatures we've had in the last week accelerates water loss, and can cause irreversible damage. It is important to keep plants well watered during heat waves to prevent wilting and scorching of leaves, and loss of flowers and flower buds that result from a less than adequate water supply. Remember that each time a plant is allowed to dry to the point of wilting, damage occurs within the plant, even if most of the plant revives with watering. Water deeply to thoroughly saturate the root zone and mulch plants to conserve moisture. Mulch will also help keep the soil cool and the roots healthy.

High temperatures can also disrupt pollination which results in no fruit being set on fruit and vegetable crops. Ornamental plants may also exhibit reduced flower life span or flower bud drop during heat waves.

Tomatoes are particularly sensitive to nighttime temperatures when in flower. They will tend to drop their flowers if temperatures stay above 76F at night. No flowers= no fruit. Pollen has a shortened life span in extremely high temperatures. If pollination does not occur before the cells die, then no fruit will be produced.

  • Extreme Cold: Cold at the wrong point in a plant's life cycle can disrupt the plant for an entire growing season or kill it altogether. Extended periods below freezing after plants have budded out in the spring are a recipe for disaster. Established plants can often recover from late-season frosts and freezes, but new plants often do not. Using sheets or other methods of covering plants for protection are useful for capturing the day's heat overnight, but will do little to help a plant withstand an extended freezing period after budding out.
  • Drought: Excessively dry periods or drought often go hand-in-hand with extremely high temperatures. Drought during pollination of fruit and vegetable crops may result in poor fruit set due to reduced life span of the pollen grains. The same advice for excessive heat holds true for drought: water thoroughly and use mulch to conserve moisture.

The drought condition that few of us pay attention to is drought due to lack of winter moisture. Lack of winter moisture can have long term ill effects on our landscape, particularly trees and shrubs. Watering trees and shrubs before the ground freezes in the fall is advisable, especially if we do not receive adequate rains. Evergreens will lose moisture through their needles all winter, so a little extra TLC in the fall is a great idea. Fall watering is especially important for plantings less than two years old which don't have the extensive root system of a more established plant.

Watering with a soaker hose or drip irrigation system is much more efficient than an overhead sprinkler. In a drip irrigation system, over 90% of the water flowing actually reaches the plants. Compare this to a traditional overhead lawn sprinkler, and only 50 to 70% of the water flowing through it actually reaches the plants. The rest is lost to evaporation.

  • Flooding/Excessive Rain: For many plants, completely saturated, waterlogged soil will kill their roots if they are kept in these conditions for extended periods of time. Well-drained soil will allow some level of excess water due to rain to drain away from plants.

Flooding presents a tougher issue—in the case of standing water around plants, it may or may not be possible to remove the water after a flood event. If an area seems prone to flooding, it would be wise to renovate the area with added drainage tiles or pipes to carry the water away from the plants' roots. Adding height via raised beds or berms may also prove helpful in eliminating excess water pooling. Or better yet, use plants that can tolerate "wet feet" or saturated soils in flood prone areas.

  • High Winds: Excessive wind can dry out or shred leaves and even destroy tender new plantings, no matter what time of year. Winds accelerate water loss in plants, often resulting in plants with a wilted, dried or scorched appearance. Protect new plantings with some type of windbreak until established. Consider using anti-dessicant sprays or horticultural oil to protect vulnerable plantings during the winter months.

Repeated abiotic stresses can weaken plants over time. A plant that has suffered through a year of drought for example, will be less likely to survive a harsh winter than a plant that enters the winter without drought stress. Abiotic stresses weaken plants and make it easier for biotic stressors like insects, bacteria, and fungi to cause damage and disease. Give plants under weather-related stress extra water and fertilizer to help them recover. Do what is reasonably possible to improve the plant's environment—improve drainage, provide windbreak, mulch properly, etc.

Ultimately, choosing plants that can tolerate harsh conditions is often the best solution to recurring problems. For example, parts of our property seem to be extremely windy nearly all the time. My husband and I chose plants that can stand up to the wind. There was no sense in choosing delicate plants for these areas. Once again, the "right plant for the right place" rule of thumb stands true.

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