How Hot Weather Effects Plants

Hot, dry summers are rough on plants, especially on non-native plants and those weak from improper care. Since many of our landscape plants aren't naturally adapted to heat, they need special attention and care.

High temperatures speed up the normal living process of plants to a maximum rate at and above 90 degrees F. This means that most plants can take temperatures up to 90 degrees F. fairly well. Anything above that—the hotter it gets, the more they suffer! Of course, less tolerant or weaker plants suffer even more. The longer high temperatures persist, the greater the injury to the plant.

Hot soils also hamper plant growth. Shallow-rooted and container plants are particularly affected by soil heat build-up. Deeper-growing roots penetrate to a level of better soil temperatures and moisture. Mulching the soil surfaces around plants and watering properly is a good idea to stabilize soil temperatures. The most obvious symptom of a plant’s heat exposure and hot soils is persistent afternoon wilting, followed by foliage burn.

Hot air, particularly hot, dry wind, causes too much moisture loss from the plant's foliage. Some evaporation from leaves is normal, but when vital moisture is being evaporated faster than the plant's ability to replace it, leaves dry out and wilt. To be drought-tolerant, plants must have roots able to absorb as much, or more, moisture from the soil and do it as fast, or faster, than the foliage loses it. First symptoms of hot air injury are drying and browning at the tips and edges of older leaves. Then, tender new tip growth wilts, soon followed by dieback. Rapid moisture loss can cause tender leaves to turn black. Evaporation cools foliage, but if it doesn't get water from the roots fast enough to provide the evaporative cooling effect, the foliage gets hot, tender growth wilts and older leaves sunburn.

Exposure to the intense sunlight of bright, cloudless, summer days can be too much for sensitive plants. Reflected light from walls and other surfaces can also add to the problem. Stunted plant growth and a yellow-white "burn" on the upper surface of older leaves are familiar symptoms of too much intense sunlight.

A good covering of leaves protects the tender bark of branches and stems from sunburn. If this shading is lost, or pruned off, the exposed tender bark will likely sunburn.

When some nutrients are reduced or limited, or their uptake inhibited, deficiency symptoms quickly appear. Such is the case with iron during hot weather growth. Wet soils, dry soils, not watering deep enough, salty or caliche soils, etc. will decrease the amount of iron plants can absorb from the soil. The yellow foliage symptoms of iron chlorosis appear as greenish-yellow leaves with dark veins. As iron deficiency becomes troublesome, the green color of leaves turns to yellow, then to white and finally brown as the tissue dies.

Using plants adapted to our hot climate is the best way to get vigorous plants with minimum care. Some plants just don't do well in the heat! They're difficult to maintain and expensive to replace. Plus, plants suffering the torment of harsh surroundings don't offer a pleasing appearance to any landscape. Native, heat-hardy or at least tolerant plants are the most practical choices for local landscapes.

Tolerant plants resist moisture loss from their foliage, and are more efficient feeders on limited soil moisture. They can better tolerate intense sunlight. Tropical plants lose water rapidly from their lush, tender foliage. To make matters worse, their less efficient rooting is often unable to replace foliage moisture as fast as it evaporates in the hot, dry summer air. Remember—plants give priority to new growth when moisture and nutrients are short, so older leaves are deprived. This is why older leaves show hot weather injury first.

The life span of non-adapted landscape plants is much shorter. As they reach maturity, they lose the natural advantage of youthful vigor and the hot climate takes its toll.

Plant conditioning is important. Just as athletes must condition for endurance, plants also can endure hot, dry weather better if properly conditioned. Plant during a season when roots can establish quickly so that they're ready to supply plant needs adequately by the time hot weather starts. Fall (September to December) is an ideal planting time for the Southwestern U.S.! Transplanting during hot weather can be an exhausting experience for plants and gardeners. Proper watering and fertilizing favors good vigorous growth and the plant will better endure and recover from hot weather stress.

Plant location is very important. Shaded locations cut summer stress for heat- and sunlight-sensitive plants. Eastern exposures or open areas are generally preferred for blooming plants. Southern or western exposures are subject to direct, intense sunlight, as well as reflected heat. Because walled areas of these hot exposures build up and hold additional heat, only very heat tolerant plants can survive in these locations. Also, consider draft and wind exposure when positioning plants whose foliage may be particularly subject to burn by hot, drying air movement.

Soils that permit deep water penetration down through normal rooting depths, yet retain good moisture and nutrient content, are also important. Such soils favor the deep, extensive root development required to maintain strong healthy growth during hot summers. Heavy caliche soils can be improved by the addition of liberal amounts of organic matter along with clean washed sand.

Irrigation IS A MUST in order to maintain good plant vigor during hot, dry summers. Proper watering year round to promote deep extensive rooting is the key to summer hardiness. Be particularly careful not to over-irrigate during cooler seasons. Too much water drowns roots needed to supply enough water and nutrients to the plant during its peak summer needs. Keep in mind that all water used by plants comes from the soil. It's the most important of plant foods.

"How long and how often to water" depends upon how long the soil retains moisture and how fast that moisture is being used. A proper balance of moisture and air in the soil is necessary for roots to breathe and do their job. Irrigate to maintain favorable, not abundant soil moisture. Water long enough during each irrigation to allow moisture to penetrate completely through the plant rooting area, but no more often than necessary to prevent foliage wilt! Following this rule, and you'll automatically adjust to the age and type of plant as well as to the differences in seasonal requirements. Deep, penetrating irrigations each time also keep soil salts washed downward out of the root area. A drip irrigation system is THE MOST effective, efficient method of watering.

Fertilizing during hot weather should be done with caution, if at all. Increased living processes of plants during hot weather use up nutrient reserves faster. However, rapid uptake of fertilizers by summer-active roots could result in fertilizer burn. Increase the fertilization frequency, but decrease the amount applied each time. Fall fertilization helps plants recover from summer exhaustion. Spring fertilization encourages strong growth to better withstand summer stress.

Organic mulches spread over soil surfaces under plants provide a practical insulation against summer heat. Mulch shades the soil and keeps it cooler. It also reduces soil moisture evaporation, therefore cutting the build-up of salt at soil surfaces. But remember, mulches retain soil moisture longer. Continue to water deeply each time, but not as often!

Pest control is very important during hot summers. Any injury or loss of foliage would be more harmful to plants during hot weather. So watch for pests and control them before severe damage is done. Apply sprays during mornings or evenings.

So, regardless of how long and/or hot the summer will be, there IS a right way and a wrong way to insure that your plants thrive and survive.

Ugliness of Fruit Produced in Hot Weather
Virus, Bitterness and Temperature

If the "beauty is only skin deep" philosophy is true, then logically, it should follow that ugly is only skin deep too. If you can accept the fact that ugly is only skin deep, and that ugly and flavor are not necessarily culinary partners, then eating the malformed, odd-colored garden produce that shows up at this time of the year should not present a major problem. Regardless of what people say, most of us eat with our eyes—if something doesn't look right, most of us will think it doesn't taste right.

The bounty of the spring growing season has peaked and gardeners are now harvesting the final products of plants which have completed their life cycle. Most of the popular vegetable plants such as tomato, pepper, eggplant, beans, etc. are annuals, which means they have a relatively short-duration production cycle compared to perennial plants. As plants begin to senesce or grow old, the "fruits of their labor" begin to diminish in quality and quantity. Add to this aging process the onslaught of summer temperatures and it seems like “vegetables-from-another-world” become a reality in your own backyard.

One of the first complaints is "biting vegetables". You take one bite out of a seemingly normal cucumber or eggplant, and the quinine bitterness of that beast will take 6 bites out of your taste buds! You may have been harvesting normal, sweet fruit from these plants all spring and then suddenly bitterness dominates. Any stress on an eggplant or cucumber plant such as high temperatures, low moisture, low fertility or foliage disease can contribute to bitterness. Bitterness is associated with fruit harvested late in the season from unhealthy, poor-yielding plants. Once a plant produces bitter fruit, remove it from the garden because all subsequent fruit will be affected in a similar manner.

What about ugly vegetables? Much of the unsightliness of vegetables is also a function of plant age and temperature. Cucumber and squash plants often begin producing misshapen and gourd-like fruit. This is caused mainly by poor pollination and/or plant stress. Improper pollination caused by the pollen being killed by hot temperatures can cause misshapen fruit. Moisture stress during development can also misshape fruit. Some pollination did occur or the fruit would not be present but incomplete pollination resulted in the abnormal fruit shape.

Folks "eat with their eyes" and some of the psychedelic vegetable colors have gotten a few squeamish people abstaining from the table. Green tomato fruit have numerous spots about ½ inch in diameter with concentric, circular markings. On ripe fruit, these markings are alternate bands of red and yellow. Some gardeners think they have produced pinto tomatoes. This colorful fruit is actually symptomatic of the virus that was contracted by the plant. The virus is called tomato spotted wilt virus (TSWV) and is spread from plant to plant by tiny insects named thrips. It is too late now to cure the problem; the fruit is perfectly safe to eat. The overall productiveness of the infected plants will be diminished. This is similar to, but not the same, virus which affects squash. Squash plants that once produced yellow fruit start to produce green, or often yellow and green, fruit. They may also have been affected by squash mosaic virus or cucumber mosaic virus. This virus is transmitted to your plants by insects that have been feeding on other virus-infected squash plants or perhaps some wild plant.

Do not confuse the symptoms of virus with the resulting effect produced by congregations of ravenous suckers called stinkbugs (so named because of the foul odor experienced when squeezed). After the fruit-suck-party has occurred, a large area of the fruit (tomato, pepper, peach, plum, pear, etc.) becomes yellow where the sucking damage has taken place. Sucking damage combined with hotter weather make the skin of tomatoes unusually tough at this time of the year.

The obvious answer to insure delightful looking as well as wonderful tasting, vine ripe servings for those who indeed believe that beauty is only skin deep and consequently, ugly is only skin deep too, is to peel the produce. My old mama used to peel tomatoes for her baby boy, but my wife decided the peeling was nutritious and a good source of natural roughage. Maybe my old mama didn't want her baby choking on those fruit skins or didn't want those tough skins getting under her dentures. I don't know who is right but I do know that my old mama NEVER put an ugly plate of tomatoes on the table, even during the summer months.