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
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
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
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
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