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Thursday, September 20, 2018

Rx for Plants with Heat Stress

   Even though we have had the hottest June and July on record, you can help your plants stay healthy by understanding a few pointers.

What is plant heat stress, how do you know your plant is stressed, and what do you do when your plants have been affected? Plants are just like people when it comes to heat stress; they have to have a certain amount of water to keep the system operating. During times of intense heat, evapotranspiration is accelerated. Evapotranspiration is the amount of water a plant takes up through the roots and releases through the underside of the leaf along with oxygen. Plants in distress show wilt, the leaves may look brownish and crisp around the edges, the plant may begin dropping leaves to shut down the evapotranspiration, branches will begin to die back, blooming stops and they pre-maturely drop the blossoms.

Stress Relief Amendments

There are several steps you can take to keep your plants healthy during our intense summer heat: deep watering, soil acidification, mulching, and use of stress relief amendments called Perk or Big Plants. The object is to keep the plant healthy, watered and the root zone as cool as possible.

Deep watering and maintaining soil that water can penetrate is key to a plant’s survival during extreme temperatures. This year even desert plants are showing tremendous stress, because of the temperatures and also because of the low rainfall this year. (As this goes to print, we are having some heavy rains in some areas of the Valley. This rainwater will help the plants). Make sure that the soil is loose enough for the water to penetrate and soak the root zone of your plants. Test your soil compaction using a long screwdriver to penetrate the soil. If the screwdriver goes in easy you have good water penetration, if it doesn’t press in easily, acidification is necessary and probably a longer duration of watering. Acidify the soil with Disper-Sul or First Step, a granular soil acidifier or if you have a severe case of soil compaction you can also use liquid palm food which is a liquid soil acidifier with micronutrients that was designed for palm trees but is also effective on other ornamental plants.

Watering Schedule

At the present time we’ve run tests and find that operating your drip system three times per week for an hour and a half each time has kept the soil profile moist enough for the survival of most plants. Plants that start turning yellow is a sign of over-watering. Then you should back the duration of the watering down to perhaps an hour and a quarter three times per week. If, on the other hand, the outer edges of the leaf start turning brown and crisp it’s a sign of under watering and high alkalinity in the soil that causes salt burn on the leaf margins. Soils will vary with their ability to accept water. If too much water is standing around an hour after you stop running your drip system, reduce the watering duration by 15 minutes. If the plants show signs of stress before the next watering time, then increase the watering duration.

Organic mulch laid on the surface of the soil also helps to insulate the soil and lower the soil temperature around the root zone. An inch and a half layer of mulch should be sufficient. For new plantings in rock areas, move granite away from the small plants to lower the temperature around the plant stem and increase its chances of survival.

Two soil amendments that have shown useful in treating heat stressed plants are Perk and a product called Big Plants. Perk is a granular product that contains humic acid and micronutrients including potassium. Locally, it is used extensively for ball fields after heavy use because of its ability to rejuvenate the cellular structure of the grass after heavy pounding by the players. It will also rejuvenate the cell structure of heat stressed plants like shrubs and flowers. Big Plants is a liquid culture of beneficial microbes, hormones and nutrients for plants. This product increases the microbial action in the soil around the roots allowing the plant to take up nutrients and moisture at a faster rate. It is extremely effective and is also great for houseplants.

Extra Care Saves $$$

The cost of the treatments is small in comparison to the appearance of your landscape. It can also save a lot if you do not have to remove dead plants and replace them. In addition to the labor and cost of new plants, the cost to remove and dispose of a tree with a six- to 10-inch trunk that is 15 feet and taller will usually run well over $300. Your investment in the Rx prescribed will reap financial benefits.

Fortunately, summer will end and the temperatures will drop. Until then, keep an eye on your plants and an eye towards a cool fall

August Gardening Calendar

Lawns & Grasses:
· Continue mowing regularly.
· Water every three days moistening soil to a depth of 10 inches.
· Fertilize with nitrogen and iron and acidify with Disper-Sul.

· Fertilize citrus trees again this month & water well.
· Harvest lemons as needed; they will hold for months on the tree without deterioration.
· Do not prune citrus trees to avoid sunburn damage.

Vegetables & Herbs:
· In late August, plant beets, broccoli, Brussels sprouts, cabbage, carrots, cauliflower, kohlrabi, lettuce, snap beans and Swiss chard.
· Set out transplants of tomatoes and peppers.
· Divide mint, garlic chives & lemon grass.
· Cut back eggplant & pepper plants to encourage new growth.
· Continue to water well.
· Prepare vegetable garden for fall planting.

· Plant begonia, celosia, coreopsis, primrose and purslane.
· Continue to deadhead spent blooms.
· Fertilize container plants and newly-planted annuals.
· Continue to water twice a week.

· Continue to deadhead spent blooms.
· Continue to deep water once a week.

· Maintain watering twice a week.
· Continue to deadhead spent blooms.

Shrubs & Trees:
· Continue to deep water twice a week.
· Lightly fertilize shrubs with tree & shrub fertilizer.

· Start planning for fall gardens.
· Monitor all plants for signs of stress; use shade cloths to protect tender plants.
· Keep weeds continuously under control.


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