Converting to Desert Landscapes Can Damage Existing Trees

Q. We removed half of our lawn with a 15 year old Chilean Mesquite in the middle which has done very well up to this point. Besides water from the lawn it had its own water supply located near the trunk. During grass removal, roots were chopped and six small plants with drip emitters in the rock mulch surrounding the tree. Will the tree be okay now that the front half sits in rock with only the plant emitters providing water.

A. The short answer is it will not. You need to supply more water to this tree or it will begin to drop its leaves and the branches will begin to die back.

Mesquite roots growing deep for water.

            Now the long answer. Chilean Mesquite is among a group of plants, called phreatophytes, which have the potential to develop a very deep root system when growing in the wild along arroyos. In the case of mesquite, 200 feet or more. This is if the tree is in the right location together with deep, infrequent rains that help establish roots to that depth. Arroyos, or desert gullies, concentrate rainwater in one location pushing water to great depths with the roots of these plants not far behind.

            Phreatophytes like mesquite when grown with water that is applied frequently grow rapidly, vigorously with a very dense canopy. In many home situations, trees do not develop deep roots because the water supplied to them, such as your lawn, is applied only to the surface few inches.

            During 15 years of growth, the vast majority of roots will grow in a “mesh” 12 to 18 inches just below the lawn. The six irrigated plants planted under the canopy will help somewhat but not enough. Removal of tree roots also reduces generally speaking, most trees can lose as much as 50% of their roots and still recover provided they get adequate amounts of water.

            My hunch is your mesquite will start dropping leaves at the onset of hot weather and you will see limb death in the canopy. The roots will try to reestablish themselves wherever they can find water but the canopy will die back because of root loss and inadequate amounts of water.

Tree dieback after converting from lawn to desert or rock landscape.

            What should you do? During this hot weather you should put a hose out there and irrigate the rock beneath the tree about once a week during hot weather. This is a stopgap measure.

            You might consider installing a “bubbler and basin” around the tree in the future to provide more water. Use an irrigation valve previously for the lawn for the water source to bubblers. An irrigation bubbler is installed 2 feet from the trunk. If this basin is quite large, two bubblers located in this basin might be needed to fill it. Each time you irrigate, fill the basin.

Mesquite blown over because shallow rooted due to lawn and flower bed

            It is important that the basin constructed is level and wide enough to lie on top of about half of the area under the canopy of the tree. A level basin, or berm, is built around the trunk approximately 3 to 4 inches high of the tree with the trunk at its center.

            The bubbler is a type of emitter that pushes out usually 1 to 2 gallons a minute. Drip emitters emit gallons in hours, not minutes, so this is a large amount of water applied in one spot in a very short. Of time. This is why the basin or berm is needed.

            If the tree is on a slope, then install the basin around the trees so that it is level. The water from the bubbler must flood the basin and be contained by the basin for it to work well. This may take 10 to 15 minutes with bubblers and anywhere from 20 to 30 gallons every time the tree is watered.

            In midsummer when it's hot this, watering might be once a week to every 10 days or so for desert trees like mesquite. Adjusting how often you water and how much is applied each time will determine how fast the tree grows and how dense the canopy is.

            If you begin to irrigate less often, but apply more water each time, you will slowly encourage the roots of desert trees like mesquite to grow deeper.

Don't Bet on Good Fruit from Rootstock Suckers

Q. I had an old peach tree of about 30 years die. We cut it down and had it removed. Last year several suckers sprouted from below the ground. They have different leaves so I know it is not peach. What are they? Should I leave them alone and allow them to grow?

A. Having a 30 year old peach tree is quite an accomplishment! They are normally a short-lived tree as far as fruit trees go. Peach is hit very hard by borers and may start to decline around 12 to 15 years of age. A 20 year old tree is really getting up there in age.

Rootstock on apricot

            When you purchase a peach tree from a nursery it is grafted (budded) onto a different tree called the rootstock. Basically, there are two different trees joined together; one is grown for its fruit and the other is grown for its roots.

            Frequently, the tree selected for its roots does not produce particularly good fruit. That is not the reason it was selected. It was selected because its roots had some particular quality that was desirable for the entire tree.

            Remove these suckers from the base of the tree. They will grow but the fruit produced will be low quality compared to the peaches that you enjoyed for so many years.

            

Select the Right Plants to Grow With Palms

Q.  I have had this palm for 10 years. Every time I add additional water with a hose or bucket I lose more fronds. Every year I cut higher on the palm to get rid of dead fronds. I drove a metal stake down 18 inches but did not pick up any visible moisture in 3 different places.  Any ideas on how I can go about this from a more scientific method?

Canary Island date palm with aptenia planted at its base

A. I did not see a whole lot wrong with your palm in the picture you sent to me. It is pretty normal for the fronds to begin to brown out and start to die once they drop below horizontal.

            In our climate it is also pretty common to have some tip burn on the leaves along the fronds, particularly as they get older and drop close or below horizontal.

            I did notice you have Aptenia, hearts and flowers, growing at the base of the palm. This plant is not complementary to a palm that has deeper roots. Aptenia has shallow roots so it is watered frequently with a small amount of water. Palms must be watered more deeply and less often.

            If you are going to plant something at the base of a palm, plant something with deeper roots that has a similar watering requirement. Replant at the base of the palm with something more deep-rooted that can give you some color.

            Select a woody perennial that give you season-long color in that spot or an evergreen with a deep root and a similar requirement for water.

Hibiscus Grows Differently in the Desert

Q. My hibiscus plant, transplanted from a pot to my outdoor flower bed, is blooming like it should. But the leaves are not getting any bigger than 1 - 1½" long and ¾" wide. The new leaves also only get to that size. I water and fertilize if with Miracle Grow regularly, but that does not help. Any suggestions?

A. The appearance of plants will be different when grown in different climate zones. I am now on my farm in the Philippines where we have Roselle hibiscus (commonly called Red Zinger) growing. I checked the size of the leaves in response to your email. I normally don’t pay much attention to leaf size just flower production.

Roselle growing on our Family Farm in the Philippines

            The leaves of our Roselle vary in size from the narrowest at about 3 to 4 inches in length and about 2 inches wide to the largest being 6 to 8 inches long and 4 to 5 inches wide. The largest leaves are growing in partial shade. The smaller leaves are growing in full sun.

Tropical hibiscus growing in the Philippines in a tropical climate.

            Appearance can also be impacted by your management practices. Let's cover a few of these.

            Climate and microclimates. Plants grown under high light intensities have a different appearance than plants grown under lower light intensities. The principal differences are in leaf size, color and thickness.

            Leaves growing under higher light intensities, provided they are getting enough water and nutrients, will be dark green, smaller, thicker or tougher and develop a thick waxy coating on the leaf surface.

            The same plant growing under lower light intensities will have larger and thinner leaves with a waxy coating that is not as thick. If light intensities get extremely high then we will see leaf discoloration, yellowing or bronzing, on some plants because the light intensity is actually damaging the leaves.

Red hibiscus growing in rock mulch in Las Vegas

            If the same plant does not receive enough light then the plant will become “leggy” with large distances between the leaves and thin stems that will not support its own weight. The plant will become "floppy".

            Our job as a manager of this plant is to find a good location in our landscape that provides the right microclimate which provides enough light for flowering and an appearance close to what we expect.

            Because we are in a desert, Hibiscus will not look similar to those grown in semi tropical or tropical climates but we can approach that look if we are careful where we plant it.

            Soil. Organic matter such as compost mixed into the soil at the time of planting and applied annually to the soil surface surrounding the plant will encourage larger and healthier leaves. I have seen this numerous times on a number of plants particularly in parts of the plants that are shaded such as lower leaves.

Red hibiscus growing in rock mulch in Las Vegas showing signs of leaf drop, leaf yellowing and branch dieback.

            Fertilizer. Fertilizer will influence the kind of growth. We know that phosphorus fertilizers are very important for flowering, fruiting, root development and production of oils in plants. If not enough phosphorus is present it will impact these types of growth.

            We do not need to apply phosphorus to a soil very often unless it is extremely sandy or growing in hydroponics.

            Nitrogen is different. Nitrogen is important for developing dark green color in leaves and stems and for "pushing" new growth. It is important in producing good leaf size and in the number of leaves and supporting stems produced.

            Nitrogen in soil available to plants also dissolves easily in water. Nitrogen is easily does not dissolve in water easily and is slowly released to plants.

            In your case you want to make sure that nitrogen is applied regularly through the growing season to maintain dark green color and "push" new growth. Combined with moderate amounts of shade, nitrogen will encourage more leaves and larger leaves.

            What should you do? Understand that if your hibiscus is in a very hot, bright location that this location will limit the plants ability to produce larger leaves. Moderate amounts of shade will encourage larger leaf development, particularly in a microclimate that gets morning sun but afternoon shade.

            Apply a 1 inch layer of compost and scratch it into the soil surrounding the plant as much as you can. When you’re done doing this, apply another 1 inch of compost to the soil surface and thoroughly wet the soil deeply. Apply a 1 inch layer of compost to the soil surface every year.

            Apply high nitrogen fertilizer at the beginning of the growing season. Apply a high phosphorus fertilizer after it is finished blooming. If you apply fertilizers at other times of the year, apply liquid fertilizers to the leaves.

            Do not apply any nitrogen fertilizers to the soil after August 1 if you are concerned about winter freezing damage. 

Texas Rangers Can Be Pruned Shorter

Q. Can I trim large Rangers so they are not so tall?

A. Yes you can and you can do it to this plant any time after the major bloom time or this winter. Texas Ranger can handle two different methods of pruning and one of those types will allow you to adjust the size of the plant more than the other method. Texas Ranger can be pruned into a hedge using a hedge shears or pruned into a single shrub.

Texas Ranger showing branches located at the base where pruning cuts can be made.

When any plant is getting too large the same general method of pruning is used to make it smaller. Some plants can rebound after severe pruning (like oleander) and others should be pruned with a more delicate touch.

To make it smaller.....First, identify one branch in the canopy which is too tall. With your eyes and hands follow this branch downward to a location where it joins another branch which is smaller. This location will be a "crotch" or "Y" where two branches are joined together.Make sure the remaining branch is growing in a favorable direction.

You will remove the taller branch by cutting just above crotch with a pruning shears that has been sharpened and sanitized. Make the cut so that the larger branch is removed and there is no remnant of that branch remaining.. The cut should be smooth with no remnant of a stump remaining. Find other branches that are to long or tall and cut them back using the same method. Vary the height of this cut above ground so that all the cuts are not at the same height.

In some cases, you may have to follow a branch a long distance close to the soil to find a favorable place to make a cut. You can remove branches at any of these locations.

If this is an older, large branch that is removed, it may leave a hole in the canopy. These holes will eventually fill with new growth from branches surrounding the hole. It will take a season for these holes to fill again so cut early enough in the season so the holes fill before winter. 

A much more dramatic but sometimes necessary method of pruning older plants is called renewal pruning. Here the shrub is cut nearly to the ground with new growth that will sucker from the cut stems.

The best time to make these pruning cuts are at the tail end of winter or very early spring before new growth starts.

Starting a Fall Vegetable Garden

Q. Could you help me get a fall garden going? Please send me a list of crops that grow in Las Vegas. I live in the northwest area off of Ann Road and Jones in Las Vegas

A. I posted a calendar for planting in the fall on my blog. Download a copy there but I will give you a rundown of the crops which are normally started this time of year in the eastern Mojave Desert.

            First, some background. There are two planting times each year. Plant cool season vegetables and herbs that withstand frost and cold during the late summer, fall, winter and spring months. Plant the warm season, winter-tender vegetables and herbs when danger of frost has passed and into the mid-summer months. Warm season crops die or perform poorly during cold or freezing weather.

            Even though it’s still hot now, this is the time of year to plant several fall and winter crops. Notice that I said many, not all. Exact planting dates vary with soil and air temperatures, the time plants require before they are ready to harvest as well as the quality of the end product.

            Cool season crops that require 60 or more days before harvesting will be just fine if planted now. It is too early to plant crops like radishes which are ready to harvest in 30 days.            

            Exact planting dates vary with your garden microclimate. Gardens located in warm microclimates have different planting dates from those gardens in cooler microclimates. If you are lucky enough to have a landscape with more than one microclimate, you can stagger your planting dates so that the same crops mature a few days or even a week or two apart.

            Plant gardens that face West or South later in the fall but earlier in the spring. Gardens facing east or north are planted in the reverse order.

            The following vegetables can be planted during September from seed or seed pieces for fall, winter and spring harvest: beets, broccoli, carrots, collards, endive, Irish potatoes, kale, kohlrabi, lettuce, peas, rutabagas, spinach and Swiss chard.

            The following could be planted as small transplants: broccoli, Brussels sprouts, cauliflower, cabbage, celery and Chinese cabbage. If temperatures are unusually hot, delay putting in transplants until weather cools off a bit.

            Mulch the soil to keep the seeds and roots of transplants moist and cool.