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Summer Plant Stress Inland & Desert
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Bulletin #TP2135
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Horticultural Observations for Healthier Landscapes |
Desert climates can be very hostile to most plants. The combination of extreme temperatures (hot or cold), low humidity, strong winds and poor soil means special precautions are needed to protect them. Understanding how summer stress affects your plants, and what you can do about it, will help you garden successfully. Here are the top four causes and cures.
WARNING: Don't prune sunburned foliage from tops of plants in summer. These damaged leaves provide protection for the rest of the leaves. Prune when the weather cools.
◊ IMPROPER PLANT SELECTION
◊ IMPROPER PLANT LOCATION
◊ Symptoms
◊ Causes
◊ Cures
◊ Symptoms
◊ Causes
◊ Cures
◊ Five Points for Good Shrub Watering
◊ IMPROPER FERTILIZATION
◊
Over & Under Fertilization Symptoms
◊ Causes ◊ Cures ◊ Pests ◊
preventing Summer PLANT Stress
in the future IMPROPER
PLANT SELECTION
When choosing a plant at the Nursery, keep in mind where you intend to plant it. Some plants do quite well in full sun, maybe even reflected sun. Other plants however do not! Then there are many plants, especially flowering plants that require quite a bit of direct sun. To provide these with too much shade will result in poor to no flowering. If it is a fruit tree, remember that flowers are required to produce fruit.
It should be noted that
the "plant care instructions" provided by the Grower (tag attached to the pot), are often not appropriate
for various Southwest Inland & Desert areas. If the Grower for the
plant is located in California, the growing conditions (full sun/shade,etc.) will
reflect that climate. The Sunset Western Gardens book is a great resource
for knowing where to plave a plant in YOUR growing area. Any Quality Plant Nursery
will have this book available for reference.
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IMPROPER PLANT LOCATION
Symptoms: Burned leaves, usually on one area (south/west facing) of the plant; discolored or cracked bark, often with oozing sap; sunken, papery areas in leaves; repeated lanky, soft growth which slowly dies.
Causes: Putting a plant in the wrong section of your landscape (micro-climate). Many plants are very sensitive to the exposure they receive during a hot summer. Some plants which are otherwise sun-loving may burn when placed by a light colored wall or reflective glass surface which faces south or west. This can also happen next to an area of paving or rock-filled landscape. Be careful of reflected sun from your pool! Also, a plant that has been in a shady area of a nursery, even though sun-hardy, may require a season (with leaf damage) in order to adjust to the sunny location.
Fruit trees and many
species of willow also have a problem with trunk sunburn, usually on the
southwest side of the trunk. Sunburned areas then ooze sap that can attract
ants, green beetles and borers. Conversely, sun-loving plants often fail to
grow well when given too much shade. Expect weak, droopy, pale growth that may
slowly shrivel and die.
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Cures: 1) Mulch the area around the plant. A good quality completely composted mulch will help cool the roots and preserve moisture. Usually a 1 to 2 inch layer will do the job. If the plant is surrounded by rock, consider using bark or mulch in a "ring" around the plant. The heat reflected from the rock adds significantly to plant stress.
2) Relocating the plant is a good idea, but during the stress of summer heat, the timing could be very bad. If the plant is not frost sensitive, transplant it during October. If it is frost tender, transplant it the following March, just after our last frost. But, what can you do for now?
3) Protect your plant. Just as you can shield plants from frost damage by covering them in the winter, you can provide some sort of temporary shade for the balance of summer. Draping nylon screening material over the plant will allow enough sunlight while protecting it against any more scorching. Do not cover with burlap during the summer.
You can protect the trunk
of sun sensitive tree with white latex, or Tree Paint.
Clean sap and debris from a sunburned trunk before painting. Many
plants increase in sun tolerance as they age and become established. It's
worth pampering them while they're young.
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IMPROPER WATERING
Symptoms: Wilting, scorched leaves with brown edges, new leaves yellowish to off-white with green veins, sudden death with a freeze-dried plant appearance.
Often a plant is in stress due to improper irrigation, and emitter placement. Too often, our watering practice is frequent (too many days a week) and short (less than 30 mins.) in time. Water Authority watering guides often recommends 4 minute watering; but this is ONLY for grass! Shrubs and trees are way different. Shallow watering produces shallow roots which are vulnerable to hot spells. Shallow watering also increases evaporation by 30 to 50%.
Over watering or under watering. These are opposite problems with much the same appearance. Which can be very tricky. The reason is simple. When under watered, the plant collapses from lack of water. When over watered, the water drives oxygen out of the soil, killing roots, keeping the plant from getting enough water and then causing it to collapse.
In desert climates, watering too often (and too shallow) is the number one cause of plant death. Most area soils are heavy, alkaline clays with layers of calcium carbonate (caliche) and poor drainage. When over watered, they become "bathtubs" full of salty water. High alkalinity, kept in constant solution by watering too often, causes nutrients to become unavailable to the plant, even if supplements are provided. The common result seen is "chlorosis"; often misdiagnosed as an iron deficiency. Plants forced to use this salty, alkaline water will dispose of the salts as far away from the roots as possible. This causes the tips of the leaves to burn and become brown and crispy with the salts sometimes visible on the leaf surface.
Over watering a lawn, or watering in the evening is likely to cause a fungus. This disease will leave your lawn with brown spots, potentially causing you to believe it needs even more water. (top)
Cures
Deep infrequent watering
produces deep roots that do not tend to dry out so quickly in the heat. Emitter
placement must be modified and expanded as the plant matures. Do not leave the emitters at
the base of the plant as it matures. The plant needs a root system that expands
just as the plant expands. Add more drippers, use dripperline. One or two
emitters at the base is ASKING FOR TROUBLE!
Five
Points for Good Shrub Watering 1) Water deeply and
infrequently, especially if you have clay or caliche soil. Deep, infrequent
water lets oxygen return to the soil, pushes salts away from the roots, allows
nutrient flow and encourages deep rooting. Run drip systems
for 60 to 90 minutes (not 10 minutes). This will push the water deep into
the soil. Use SLOW RATE (1 gph) drips. You will not be using excessive water.
Running your system 2 or three times a day for 5 or 10 minutes
does not allow water to penetrate deeply, is wasteful and
will cause you much trouble in the long run. Infrequent water is never "every
day".
Scheduling will depend on your soil, the plant and the temperatures for the
decision of "how often". Check Bulletin #TB1110
"Watering Considerations for Shrubs and Trees"
2) If you are lucky enough
to have very good drainage, you'll water more frequently than those with slow
draining soils. You may need to use a moisture meter to determine how often to
water. 3) If your trees and
shrubs are on the same irrigation cycle as your lawn, separate them if you possibly can.
Irrigation consultants can help you. 4) For bubbler systems
(flow rates in excess of 10 gph), run at least 10-15 minutes for good coverage. 5) A layer of surface
mulch helps tremendously by conserving moisture, cooling the soil and enriching
it. If you have salt buildup, shown by a white crust on the soil, flush the
area twice a year. Use an acidic product like Aluminum Sulphate to lower pH and improve
soil porosity.
(top) Lawns and flowerbeds generally
will need more frequent watering. These, by nature have shallow roots. If your
lawn has brown patches and a generally washed-out, unhealthy appearance, the
first step is to make sure your sprinkler system is working properly. Be sure
you water at the right time of day (never between hours of 7 PM and 2 AM).
Do not utilize high nitrogen
fertilizers during the summer. They promote plant growth, which adds to plant
stress. If the plant actually needs fertilizer use a low nitrogen organic product
(4-6-5 or equivalent)
These 5% nitrogen fertilizers will provide vital food for soil biology
and thus nutrients for your plants root system. The added some phosphorous for
flowers, potassium for heat stress, and avoid stimulating growth.
Over &
Under Fertilization Symptoms:
Over - Blackened or scorched leaves, excessive leaf drop,
general unhealthy appearance, even with proper watering. Too much fertilizer
can also cause overly lush, top-heavy growth leading to wind damage and
increased insect and fungus attack. Under - General yellowing of plant, especially on older
leaves; small, stunted leaves on tips of branches; weak, spindly growth; little
or no yield on fruit and vegetable plants. Causes: Too
much fertilizer; the wrong fertilizer; not enough fertilizer. Cures: It's
easy to over fertilize, especially in hot weather. On the other hand, plants
which are undernourished are unhealthy looking and prone to other summer ills
like windburn and chlorosis. Make sure you have the right fertilizer for your
plants at the right time of year and always follow package directions. A word
of advice--if you're not sure, it's better to use too little than too much,
especially in hot desert climates during summer. You can always add a little more, but you may
kill your plants if you apply too much. If plants show signs of over
fertilizing, deep-flood water the plant 2 times; one week apart to remove fertilizer
from the root zone and cross your fingers. Pay attention to what time
of year a specific fertilizer should be applied. Bag instructions should
specify if temperature is a consideration. Some fertilizers release their
nutrients much faster in hot weather. This increases potential for damage.
Other kinds won't release in cold weather at all. See Bulleting #TP2600, Fertilizer
Basics, for a description of fertilizer types. Wind Damage: Don't
plant brittle trees in high wind areas. Be sure to properly stake your trees.
Improperly staked trees can be damaged by breakage or rubbing bark against
stakes. When the hot dry wind blows, and blow it will, plants use more water.
Extra watering might help, especially on broad leafed and newly planted
specimens. Pests: Fungi
and insects can and do attack in hot weather. Proper and complete diagnosis of
the problem(s) is vital to an effective cure. Good troubleshooting will require
examining many aspects of the plant and its' care. A Certified Nursery Advisor can
help you. You may need to return to your yard to find all the answers. When all
the culprits are identified, treat with insecticides or fungicides as needed. preventing Summer PLANT Stress in the future Learn the needs and
tolerances of your plants. Don't be fooled by a grower labels. Do some
independant research. Each Spring, check out
your irrigation system. Read Star
Note #910 "Irrigation Tune Up." Help expand your plants root systems by
adding drips further away from the plants base. Use Mulch! Do proper
fertilization; a healthy plant can withstand much more heat stress than a
weakened plant. Grow fruit trees and
willows with low branches that shade the trunk. Paint exposed trunks of young
trees with a white, water-base paint. Additional reading: Plants
for Dry Climates, by Duffield & Jones is a good source;
the Sunset Western Garden Book is another.
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The GC-Pro-I Irrigation calculator
can make the complex job of scheduling - Easy.
(top)IMPROPER
FERTILIZATION
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Use of proper planting techniques helps a great deal. See StarNote 001, Planting
Guide, for some ideas on how to get your new plants off to the right
start.
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