Stressors that Affect our Plants
Most of us have heard of the U.S. Department of Agriculture's Plant Hardiness Zone Map (Zones 1 thru 10) that
helps us determine whether plants will winter over in our part of the country; but AHS, or the American
Horticulture Society, has developed a heat map to help us determine which plants can tolerate the type of
heat our plants may have to deal with.
To learn more about the AHS Heat Map, click here AHS
Heat Map
Often plants exhibit problems that are automatically attributed to insects or disease when in fact the
real problem is in the plant's environment. A plant problem that is not caused by a living organism
is called an abiotic injury. This type injury may be caused by drought, excess water, exposure to low light or
extremely sunny conditions or possibly poor soil conditions. Selecting plants suited to your location can
save you money and aggravation.
Drought: Leaves curl and plants wilt when the roots are unable to supply sufficient moisture to
stems and leaves. Often we see our plants wilted in the late afternoon; wilting for short periods of time
will not harm your plants. The plant's survival mechanisms kick in when moisture is evaporating from leaves
faster than the roots can replenish moisture; however, over a prolonged period of time, drought will cause
serious damage such as yellowing, leaf scorch, browning, leaf drop or stunted growth. Extended periods of
drought will also inhibit flower formation.
Excess Water: Usually caused by overwatering or poorly drained soils, excess water reduces oxygen
in the soil which damages fine roots and renders the plant unable to take up water. Plants will exhibit the
same symptoms as plants under drought stress; i.e., wilting or yellowing of lower and inner leaves. If excess
watering continues, plants may begin to show scorch, leaf drop and/or plant death. So to avoid this problem,
where needed, select plants tolerant of moist soils or adjust your watering practicies and allow the soil to
dry between watering.
Insufficient Sunlight: If plants require full sun, you will want to make sure they have full sun
for at least part of the day. Sun-loving plants growing in partial shade are unable to produce as much growth
as those living in full sun due to reduced photosynthesis. They will begin to exhibit elongated spindly growth
with fewer side shoots and thin, pale colored or yellow leaves. The leaves will oftentimes be larger and thinner
than leaves of the same species growing in full sun. This allows more surface area for photosynthesis.
Excess Sunlight: When a shade-loving plant is planted in full sun, leaf scorch or sunburn will appear.
Strong sun and heat causes the breakdown of chlorophyll in the leaf and damage appears as pale, bleached or
faded areas. These will eventually become brown and brittle. Symptoms will be more severe if the strong
sun is combined with dry soil conditions. Most shade-loving plants will tolerate morning sun as long as
moisture levels are maintained; but be sure to avoid planting shade-loving plants in locations exposed to
strong mid-day sun.
What's that old saying? Location, location, location. I guess that holds true for plants too.
Below is a listing of plants proven to do well in hanging baskets in a southern garden with summertime heat and humidity.
Abutilon 'Apricot' has large dark green maple shaped leaves with orange bell flowers. Pinching will
promote branching.
Cuphea 'Dynamite' has fine textured foliage and tiny, bright orange tubular flowers with black
and white variegation on the tips of the flowers resembling ashes on the end of a cigar. The plants are
self-branching and therefore do not need pinching.
Evolvulus 'Blue Daze' has green pubescent foliage with striking blue flowers. Pinching will promote
branching but delay flowering. Flowers profusely in a sunny environment.
Helichrysum 'Golden Beauty' is a strawflower that produces many long-lasting, mustard colored
flowers but is unlike strawflowers in that it has a low-growing, spreading habit. Relatively heat and drought
tolerant but the plant needs to be cut back and deadheaded regularly to look neat through the summer.
Pentas 'Starburst' thrives in heat and drought blooming all summer. This cultivar is more compact
and ideal for hanging baskets. Pinching will delay flowering but increase vegetative growth and thus the
number of flowers.
Purslane 'Apricot' has succulent green foliage with papery bright orange flowers. Flowers open
around 10 a.m. and close in the afternoon.
Scaevola 'New Wonder' has lobed green foliage with purple fan-shaped flowers.
Streptocarpella 'Concord Blue' is an excellent plant for hanging baskets. The plants produce
abundant flowers throughout the summer. Pinching does not improve branching. Hummingbirds are attracted
to the flowers.
Tibouchina 'Spanish Shaw' has purplish bronze foliage cascading over the basket and bright pink
flowers with yellow stamens. Tibouchina is a self-branching plant, so pinching is not necessary. Each flower
only lasts one day, so there is never a full set of flowers covering the plant; however, this plant can certainly be
appreciated for its unique foliage and lush growth.
Verbena 'Trailing Katie' is a traditional large-leafed verbena with pastel pink flower clusters.
This plant will continue to bloom throughout the summer as long as spider mites are controlled.
