Advice During the Heat of Summer

Q. Can you give some tips to on how to survive this latest bout of heat? Is it simply too hot right now for plants? Is shade cloth the answer?

A. It has been hot these past few weeks and very stressful for many landscape plants. There has been a combination of high temperatures, intense sunlight, very low humidity and windy conditions. Just like us, healthy plants have the best tolerance to the extremes of heat and cold. But water and fertilizer can be a killer if too much is applied.

            Shade cloth is helpful in some situations but it is usually for vegetables. Use shade cloth to manage the intensity of sunlight and reduce sunburn on tender vegetables. Shade cloth providing somewhere between 30 to 50% shade is used with these plants. Otherwise, rely on leaves of plants to provide their own filtered light.

Avoid watering trees, shrubs or any plants that are woody every day. Try to give these plants at least one day of rest, without irrigation, between waterings. Some landscape plants have roots that suffocate easily if the soil contains too much water. These plants seem to “die overnight” when watered daily or the soil remains wet.

Mulch helps. Mulch of any kind, whether it is rock or wood chips, applied to the surface of the soil helps cool it, preserves soil moisture and helps battle weeds. Rock mulch applied to the surface of the soil is best for desert species of plants. Woodchip mulch is best for non-desert species of plants. A surface layer of mulch can add one or two extra days between irrigations.

A wet sponge drips water because it can hold no more.
A sponge is moist after it has been squeezed.

Water just before the heat. Make sure plants enter the heat of the day with their roots surrounded by moist soil. There is a difference between “wet” and “moist”. This is particularly true of plants grown in containers. These soils dry out faster than soils in the landscape. Plus containers warm their soils faster compared to landscape soils. Wet or moist soils warm up slower than drier soils.

             

Water lawns early in the morning. Apply lawn irrigations as close to sunup as possible but when still dark. Windspeed is usually slowest at these times. Never put a lawn “to bed” wet. Give the leaves a chance to dry off before it gets dark. This helps avoid lawn diseases.

            

Fertilizer can be applied now. You can apply fertilizers this time year but use half the recommended rate and apply it when temperatures are cool, during the mornings or evenings. Make sure dry fertilizers are rinsed into the soil immediately after they are applied. Lifertilizers can be sprayed on leaves but only during morning when temperatures are cool.

             
Some pruning can be done now. Light pruning can be done anytime during the growing season. Never use anything bigger than a hand pruner this time of year. Use saws and loppers only during late fall winter and early spring. Don’t remove too much. Always leave some growth to shade the trunk, stems and branches.

Water Bermuda Grass Sod Once Daily but Thoroughly

Q. When laying hybrid Bermudagrass sod, does it make sense to water two or three times on hot days?
 

A. Freshly laid bermudagrass sod should be watered once a day. Make sure the soil beneath the sod is wet and not just the sod itself. Bermudagrass is a very fast grower and loves the heat when it's roots are in wet soil and there is plenty of nitrogen fertilizer.. Avoid sprinkling the sod just enough to wet it. It needs more water than that.

This was tall fescue sod laid in the middle of summer on very hot, dry soil. The hot dry soil burned the roots of the sod causing dead patches like a disease. Fescue sod is hard to establish during the heat. Bermudagrass and other warm season grasses like St. Augustine or zoysia should be laid during the early heat of summer..

            Water and nitrogen. Bermudagrass sod needs water and nitrogen fertilizer so that its roots can “knit” into the soil beneath it. When watering, make sure enough is applied to wet the soil several inches beneath it. As you begin mowing, increase the amount of water applied and try to water every other day during the heat. This forces its roots to grow deeper and the grass will become more drought tolerant.

            Hopefully a phosphorus fertilizer was applied to the soil before laying the sod. If not, then apply one now. Use a single application of 16-20-0 at a rate of 2 to 3 lbs of fertilizer per 1000 square feet and water it in immediately after application. 

            Applying nitrogen fertilizer frequently. Apply nitrogen fertilizers once a month during establishment. Apply 21-0-0 at 3 lbs per 1000 square feet. Once the lawn is established in about 3 months, reduce fertilizer applications to three or four times per growing season.

Yellowing Leaves Can Mean a Lack of Water

Q. Our Acacia and other trees in our neighborhood in Mesquite, Nevada, have leaves that are turning yellow. Is this from all the heat we’ve had or too much watering? 

This is citrus but leaf yellowing accompanied by scorching of the edges is usually a good indicator the plant is not getting enough water. The solution is not to water more often but to give it more water when you do water.Scorching and yellowing of the leaves can also mean some salt problems. Salt problems can happen when plants aren't getting enough water. Flush the soil around the plant with high volumes of water a couple of times.

A. This extended heat wave requires you to water more often. But water long enough to wet the soil deeply. Avoid watering daily, particularly trees and shrubs. It is not needed if you water deeply. It is better for the plants if you don't. Instead, increase the number of minutes so that you can avoid watering every day.

            Healthy plants can handle the heat. Leaf yellowing is not because of heat but because of either dry soils or soils that are continually wet. Continually wet soils can occur from daily watering. Watering desert adapted plants every day may cause their roots to “suffocate” from too much water.

            Watering less often, but with larger amounts of water, forces roots to grow deeper and harvest water from greater soil depths.

            Plants are lazy. Plants require more energy to harvest water from deep in the soil than from the surface of a soil. If water is applied to the surface every day, these lazy plant roots “slurp” up the surface water and hardly touch the deeper water, if there is any.

            If water can be found deep in the soil and the surface of the soil begins dry, tree roots will be forced to grow and harvest water from these deeper, wet soils. This deeper growth improves anchoring of the tree and reduces “blow over” during high winds.

            If you are going to make a mistake when overwatering, make the mistake of giving the plant too much water rather than watering daily.

Irrigating Big Pine Trees Requires Lots of Water

Q. What is the optimal watering and fertilizer schedule for desert pines? I started taking care of a large horse property two months ago. Many of the trees were in distress from lack of water and fertilizer. I've been watering about 5 gallons per tree per day and the trees have responded with new growth and color.

A. Five gallons of water per tree per day is not much. Watering this way forces tree roots to grow along the surface of the soil. It does nothing to encourage deeper growth. Deeper root growth is important to  prevent them from blowing over during high winds. It is also important for their tolerance to dry conditions.

            I understand they were in bad shape but with the amount of water you are giving them they will never become lush and dense. The density of most trees increases with increasing amounts of water. Tree density decreases with lesser amounts of water.

            Larger trees require more water. Smaller trees require less water. You can decrease their water use through selective pruning to control their size if their water use is a problem.

            It is difficult to estimate how much water they need. But the amount of water they will need in one year is roughly equivalent to the volume of water 4 feet deep under their canopies.

             

Let's do some math. Estimate the cubic feet, 4 feet deep, under the canopy.First calculate the area under the canopy. Use 3.14 x half of the diameter squared. If the diameter of the canopy is 20 feet, multiply 3.14 x 100 which is 314 square feet. Now multiply 314 x 4 to get the cubic feet of the area 4 feet deep. The cubic feet of water needed by EACH pine is 1256 cubic feet.

Multiply the cubic feet by 7.48 to estimate gallons of water. This will be about 9320 gallons of water consumed by each tree this size each year. About 2/3 of this water, or about 6100 gallons, will be used from May through October. The remaining 1/3, about 3100 gallons, will be used from November until May. 

Water less often but with more water. Depending on the soil you have, water once or twice each week during the summer months. Water less often than this during the fall, winter and spring months.Give each tree enough water so the water will drain at least 2 feet deep around the tree. It is very important to give these trees the same amount of water each time you irrigate them. A surface mulch of wood chips in these basins, at least 4 inches deep, would help these trees considerably.

 

You can't see it very well but there is a basin around this pine tree. I would make this basin deeper so that it will hold at least 2 to 3 inches of water. Large basins may require 2 bubblers or 2 rings of drip emitters around the tree.

            Trees of this size might be best irrigated using a basin around each tree trunk. The trees are watered by filling this basin. The basin should be constructed at least half the size of the trees canopy.It does not have to be round but should be located where you want most of the roots to grow. If these trees are close together, you could group 2 or 3 trees with a shared basin. Just make sure each of the basins are level.

The basin is also a convenient place to apply fertilizer or horse manure, in your case, once or twice a year.

Pine Trees Produce Sap When Healing

Q. One of the pine trees in my backyard has developed a split in the bark and is oozing some sap. The trees were planted about 10 -12 years ago and are now 12 -14 "in diameter. Is this something we should be concerned about?

None of these pictures are from the reader but it is easy to see that pine trees, when they are injured, produce an abundance of sap.

A. If the trees appear otherwise healthy, most likely not. When pine trees have wounds, it is normal for them to “leak” sap. It is their way of healing from wounds.When you do see sap from pine trees it is an indication that there was damage done.

            Make sure the tree is getting enough water. Also, make sure it is not watered too often.Having adequate water speeds the recovery from wounds. The trees canopy is a quick way to know if your pine tree is receiving enough water. Dense canopies with lots of new growth is a good indicator enough water is being applied.

            Water these trees deeply but infrequently. In other words, give them big drinks of water and then hold off as long as you can before the next irrigation. Deep irrigations 2 or 3 times a week should be enough.