Why Not Encourage Winter Planting in the Warm Desert?

Q. Why do you encourage people to avoid planting during the winter months? I can understand it in Minnesota but why southern Nevada?

Oleander winter freeze damage during a particularly cold winter.

A. Simply because I don’t know what is going to happen. I tell you spring and fall are the best times to plant. If it is a warm winter. then planting during the winter is okay. But if it is a cold winter, such as the lower teens at night, then be careful! Plants need soil at least at 45 -50F to grow roots. Otherwise the roots just sit there until the soil warms. 

Winter Freeze?

Cold or freeze damage to myoporum (locally known as Australian racer).

Will it freeze this winter or not? If the plant is winter tender, like bougainvillea or most citrus, then you are playing Russian roulette with the winter temperatures. It is best to plant those (that might freeze during the winter) in the spring for that reason.

Winter freeze damage to bougainvillea.

Watering Yucca in Winter

Q. Should I turn off the water to my yuccas during the winter?

Yucca rigida with golden barrel cacti beneath it. Y. rigida is a native to the southwest and, along with golden barrel another native cacti to the southwestern deserts, can be watered less often than yucca not native to our deserts. Examples of Yucca not native to the soutwest include Y. gloriosa and Y. filamentosa.

A. It depends on the yucca and where it came from. Some yucca come from dry regions and others come from wetter regions. I would not irrigate as often yucca native to the southwestern US. Examples include Yucca rostrata sometimes called Adams Yucca or Beaked Yucca, Y. schidigera and Y. elata as well as others.  I would water them once during the winter months of December and January. These are xeric in their water needs. That is the time to give them a good soaking. Confused yet? Ask your nurseryman which yucca it is before you buy it. Put Yucca native to the deserts of the southwest together so you can irrigate them at the same time. 

Yucca elata, soaptree yucca, is also native to the deserts of our area. Plants surrounding it, golden barrels, are also native to this area. The landscaper did a good job of grouping plants together with similar watering needs.

But yucca native to the southeastern US (such as Yucca gloriosa sometimes called Spanish Dagger and Y. filamentosa sometimes called Adams Needle as well as others) should be irrigated once every two or three weeks during the winter. Water these as you would any other landscape plant. They are mesic in their water needs. Put non desert yucca together so it is easier to irrigate them because they should get watered more often.

Probably Yucca rigida, a desert native. Probably watered too often.

Iceberg Roses Have Holes in Their Leaves

Q. I am growing iceberg roses and have noted holes in the petals of the flowers. I have taken this problem to nurseries, and they are stumped. Do you know what causes this?

Iceberg roses with holes in the flowers.

A. The shape of the damage to the petals can give some clues. If the shape is circular and smooth, or near circular, then it is probably damage from a leaf cutter bee. These bees cut holes from flowers that are nearly circular and about the size of a dime. They are great pollinators when they are active.

Holes Due to Leaf Cutter Bees

            Since these are solitary bees and the female cuts these circles for egg-laying, they start showing up when it gets warm, in about April and then through the summer. That’s why they make good pollinators for apples, pear or other late or continuous bloomers. You will not see these near perfect circles show up until that time. If the holes have jagged edges around their outside, then most likely it's a chewing insect or possibly snails/slugs.

Leaf cutter bees make nearly perfect circles or near circles in leaves and flowers of plants like this pepper leaf.

Holes Due to Slugs or Snails

            You will have to do some detective work if the holes are not from leaf cutter bees. Snails and slugs are the easiest to detect because they'll leave a slimy trail on leaf undersides when they do their damage. If you think its snails or slugs, then spread out wet newspaper or cardboard just before nightfall. They like darkness and moisture. so, the dark and moist undersides make perfect traps. Squeamish fingers will pluck them from this underside for execution.

Slugs or snails can leave holes in leaves but usually leave a slimy trail behind. The browning of these lettuce leaves is wilting damage as well.

Sticky Traps

Sticky trap in greenhouse for insect trapping.

            If it’s not snails or slugs, then make or buy sticky traps. These can be made by hanging yellow sticky 4” x 6” business cards close to the damage and covering them with a sticky substance. Smeared Vaseline jelly will work but not Vicks!

Get Bottle Trees out of Containers and Into the Ground

Q. I am growing healthy bottle tree in a very large concrete container in Queensland, Australia. The lower branches have been turning brown and then falling off. Is this typical behavior as this tree grows taller or a water problem? I am watering maybe 2-3 times a week using a handheld hose.  We are currently moving into our summer with very warm to hot days.

A. All bottle trees (Brachychiton populneus and B. rupestris) growing in containers or pots presents its own set of problems (primarily heat, soil, and water management) that growing them in the ground does not. I would encourage you to think about planting in the ground if possible. Our bottle trees get big! So do Australian-type bottle trees!

Bottle Trees in Australia are Different Than Ours

            In Australia they sometimes call Brachychiton rupestris a bottle tree. In the US, Brachychiton populneus is called the Australian bottle tree. Both are natives to you but rupestis gets the typical bottle look when younger while populneus gets a bottle shape that is not as exaggerated. Dropping of lower limbs may be natural with that species if they get eight years old. Hard to know since it depends on how old it got and if the trunk was starting to swell.

Be careful when putting bottle trees in lawns. These trees don't like lawns because lawns are watered too often. They are native to Queensland and Victoria, New South Wales, Australia and prefer soils that have good drainage and are not watered frequently.

Heat Management of Containers

I would suggest growing them in double pots. The outside container creates shade and acts like a heat protector for the roots. When the sun shines on the pot directly it can damage or kill about 50% of the roots due to heating up of the soil.

            The surface of dry containers, when the air temperature is 105F, is about 175F. Plant roots can handle temperatures at about 135F. I tell people to water their plants just before the heat of the day. As trees get older their roots occupy more of the container and this can be a significant problem during the summer. Root growth occupies space.

Bottle trees, Brachychiton populneus, can sunburn on upper branches because of its thin bark. It is easily vandalized as well.

Soil Management of Containers

Soil in containers “wear out” (depletes) in about five years and should be changed or amended every three to five years. I would discourage you from growing a large tree (bottle trees mature at about 50 or 60 feet) in containers. Most containers are not large enough to handle tall trees and their roots as they get larger. Containers are better suited for smaller plants like limes, calamondin, and finger limes.

Water Management

The usual problem with bottle trees is poor drainage and watering too often. The roots will rot if they get a continuous water supple and the soil stays wet. Digging them up when roots are rotting is usually accompanied with a putrid smell as the roots rot. When watering by hand about one fourth of the applied water should come out the bottom to remove salt.

            If you can’t control the water in the soil (drainage) or the application of water, then plant the tree on a “hill” that is at least one foot higher than the surrounding soil and six feet in diameter. Cover the soil with a 2-to-3-inch layer of surface mulch, either rock or woodchips.

Chosing One Product for Pest Control

Q, If you were to buy one product for insect control on plants, what would it be?

Organic castile soap for mixing in an emergency. What you shoot, is what you get when using soap and water sprays!

Probably the single most important insecticide all season but it is applied in the winter as a precaution. Insurance insecticide.

A. Probably soap and water sprays or an oil but not a Neem-type oil. Soap and water sprays are deadly to all insects whether the insect killed is a good guy or a bad guy. With soap and water sprays “what you spray is what you will kill”. Be careful when you use soap sprays and spray only what you intend to kill. In many ways it's like a gun.

            The advantage of industrialized pesticides is that they stick around longer after you spray them. Soap and water sprays must be repeated more frequently to protect plants from undesirable insects but are perceived as more environmentally friendly. I always carry with me a bottle of soap for mixing with water in case I see an insect problem that needs my immediate attention.

            In a pinch you can make your own soap spray by adding about one to two tablespoons of dishwashing soap to a gallon of water. I prefer using a pure Castile soap, that I am comfortable about, to mix with water.

            The oils I'm talking about are the “horticultural oils” or “dormant oils” made from paraffin or mineral oil and not from the Neem plant. These types of oils have been proven to be very effective on soft bodied insects like scale, aphids, mites, and whiteflies. Follow the label directions when making an application. Don't add soap to the concoction if it is already "homogenized" and has something in it that already mixes the oil and water together.

Horticultural oils (don't use Neem oil) comes in smaller and larger quantities.

Bottlebrush With Open Canopy and Yellow

Q. I have a bottle brush shrub that is open and getting yellow. What to do?

A. The Australian bottle brush plant is sold as a shrub but can reach heights of 25 feet so it can also qualify as a small tree as well. Bottlebrush varies from dwarf types to trees and flower color from red to white to pink. 

Flowers of the red bottlebrush.

Later the flowers produce this which are seed capsules.

Dwarf Types

Just don’t use dwarf types like ‘Little John’ if you want a larger tree sized plant. In tree form it can be used on single story homes for shade. To be on the safe side plant it away from hot walls. There is a weeping form and a non-weeping form as well as dwarf varieties. Also flower color can range from yellow to red and shades of red to pink and white.

One of the dwarf types, don;t know which one, with freezing damage.

Yellowing Leaves

            It oftentimes has a problem. Yellowing of the leaves oftentimes occurs when the soil is low in nutrients as well as its organic matter content. Fix yellowing by applying a landscape fertilizer every year in the spring and combine it with an annual application of chelated iron. Enriching the soil with organic matter is done when you used small rocks by raking them back and applying a thin layer of compost to the soil, wetting it, and raking the rocks back. Large rocks may not need raking. The compost and fertilizer will just wash through it to the soil.

One of the iron chelates, EDDHA. I prefer this type of iron chelate because it is stable regardless of the soil pH. Other iron chelates like EDTA and DTPA iron chelates become ineffective at soil pH above about 7.6. Apply it early in the growing season when you make a fertilizer application.

Increase Density of Canopy

            To improve the density of its canopy, make sure it gets enough water. The plant grows best if treated as a “mesic” plant rather than a desert or xeric plant. It grows well when surrounded by lawn. Water should wet the soil about three or four feet in diameter to a depth of about 18 to 24 inches deep each time. Water it as you would any mesic plant such as ash, bottle tree, African sumac, and others. As this plant approaches ten feet tall then wet the soil about five to six feet in diameter. Another possibility might be low soil organic content. So rake the rock away and put a thin layer of compost on top of the soil, water it in and replace the rock.

Pruning to Tree

            To get a small tree out of this, remove the lower limbs when it is 3 or 4 four feet tall so that the canopy occupies about 2/3 and the trunk is about 1/3 of its height. Plant it at least five feet away from hot walls or it will fry. Also in the desert remove lower limbs slowly as the lower limbs touch the ground. Otherwise the trunk may get sunscald.

How to Reduce Water Use in a Condominium HOA; Part 2.

 In How to Reduce Water Use in a Condominium HOA; Part 1 you determined what plant water use category you are in; 

Landscape water use categories

0-2 feet of water covering the irrigated landscaped area (nice job!)

3-4 feet of water covering the irrigated landscaped area (not bad)

5-6 feet of water covering the irrigated landscaped area (too much water used, scale back!)

Cranking the Water Use Down

If you are not happy with your landscape water use, or want to save even more water than you have, first consider eliminating trees above the roofline of the condos or at least pruning them lower. Are large trees important? Yes they are but perhaps not nearly as important as the cost of the water they need to survive.

These pine trees are planted too close but the shade they produce can't be denied. As these pine trees get larger, the cost of watering them may be worth more than the shade they produce. It will be up to you but consider removing them after replacement trees have been established.

Big Trees Use More Water than Little Trees

It may sound comical but people buy trees that grow 50 feet tall and only need a tree that is 15 feet tall (single story homes). Examples are pine trees. Sure pine trees may not use as much water as a mulberry but it still uses water. The bigger it grows, the more water it needs. Plant or keep trees that shade the walls and windows on the south and west sides of a building.

This hot, west facing exterior wall has four small shrubs that create no shade on the wall but still require water. Their distance apart (about 10 feet) would provide the water needed to plant and locate three small trees or shrubs (ten feet tall) that would shade this hot wall. As the plants we chose to replace them got larger, more water should be added. Add one more small tree (patio tree) to provide shade for the patio area walls and door.

Selecting "Backbone" Trees and Large Shrubs

Selection of "backbone" trees and shrubs should be hardy, deciduous, and survive temperatures to at least 20F during the winter. What are backbone trees and shrubs? These are trees and shrubs you don't want to lose to winter freezes. The trees and shrubs should be deciduous because we want the sun to warm this condo in mid-winter. If you want to save even more water, use small deciduous desert (xeric) trees and water them separately from the more frequently watered mesic plants. 

Landscape "Negative Space"

The fewer plants used and the smaller they are will, for the most part, determine how much water your landscape uses. Deserts use less water by NOT growing plants. I call not planting.... "negative space". Where are plants needed? Where are plants NOT needed? Leaves these spaces open. Creative use of negative space is challenging. In the wetter, eastern US lawns were used to occupy negative space. In the desert we must be more creative; boulders, changes in rock size (texture), changes in elevation, artwork, wall paintings...all can be important when not using water.

Dry washes can use textural changes along with plants. Rocks don't use water.

Open spaces don't use any water and the plants used were desert in origin (xeric) so they aren't watered very often. I would substitute small trees near the windows.

Textural change in the mulch and wall paintings add color and interest to an otherwise somber area and don't use any water. What is the water use here?

Planting in Desert Soil

Locations of ten foot tall trees or shrubs should be 4 to 5 feet from the home. Taller trees and shrubs can be planted further away. 

Soil amendments should be lightly mixed with the soil at planting time along with water. 

Planting holes should be wide and not necessarily deep unless there is a clear drainage problem. If a slight drainage problem exists, plant on a mound of amended soil rather than digging deep.

Water should be applied away from the foundation of the home. In the desert, plant roots follow where water is applied.

Trees and shrubs should be fertilized once in the spring. Two times at most. Showy plants are fertilized three or four times a year and when they flower best.

Trees use water. Bigger trees use more water. Lots of big trees use lots of water

How Much Water Do Pine Trees Use?

Q. We have on our street in Las Vegas pine trees that are over 20 years old and 50 feet tall. We obviously want to ensure their survival as we try to conserve water. Approximately how many gallons of water would each tree require each month?

A. The exact water requirement for pine trees is going to be difficult because water use of pine trees has never been quantified in our desert climate. Even if they have, those amounts are "ballpark amounts" and close approximations. Every site is different. Every year is different.

Mature pine tree about 35 to 40 feet tall and 50 to 60 feet wide. The area to water is at least 25 feet in diameter to stabilize the tree and spread the water it needs out. Can a smaller tree do the same job? It may use less water.

Approximate Water Need

I can approximate. We do know that as the tree gets larger it needs more water to grow healthy. Its annual water use is probably between 4 to 5 feet (48 in. to 60 in) of water applied under its canopy and surrounded by bare soil or mulch. This is approximately what it might need when its not surrounded by grass. Grass of mixed landscapes makes it cooler and it uses less water BUT not good for pine roots and its health.

Increase Water Estimates: Plant Need + Salts + Water Lost When Irrigating

If the tree is being watered by city water (because city water, not most well water, has salt in it) then it will need to be increased by about 20% to compensate for mixing in Colorado River water with it. Then, on top of all that, you must figure in losses due to imperfections in the irrigation system. If you are using drip irrigation, that water loss will be about another 5 to 10% beyond what it needs. 

                                                       Water needed by the plant

                                                                            +

                                          Las Vegas' salty Colorado River water (20% more) 

                                                                            +

                                  Water lost by the irrigation system (varies from 5 to 45%)

I will just guestimate what pine trees need. Add another 25% on top of that to compensate for Colorado River salts and another 5 to 10% if using drip irrigation. The water lost each month depends on the weather so I will give you approximate values. If it is a colder than normal month, the trees use less. If it is hotter and windier than normal, the trees use more.

Irrigate Following the ET Curve

The water use will follow a bell-shaped curve like the one below. These amounts relate best to tall fescue lawns.

Annual water use of adequately watered tall fescue in Las Vegas, Nevada. (Month 1 = January, 12 is December). Water needed by green and growing tall fescue lawns is about 1/10 of an inch of water each day in both December and January. This adds up to about 75 to 85 inches (7 to 8 feet) of water use per year. Pine trees don't use as much water as this tall fescue lawn so its water use is about 4 to 5 feet of water (48 to 60 inches) applied under its canopy each year. Water use is in inches of water use per day when the sun is shining and very little wind. The larger the tree, progressively, more water is needed by the tree. As trees get bigger, they need more water.

Monthly Water Use

January tall fescue lawns in full sun use about 0.1 inch per day;  so pine trees may use about 2 inches in 30 days if applied evenly under the canopy.

February a tall fescue lawn uses 0.14 inch per day; so pine trees may use about 3 inches

Following the same reasoning:

March 0.19 inch per day; 4 inches

April 0.28 inch per day; 6 inches

May 0.36 inch per day; 8 inches

June 0.41 inch per day; 9 inches

July 0.40 inch per day; 9 inches

August 0.35 inch per day; 8 inches

September 0.28 inch per day; 6 inches

October 0.22 inch per day; 4 inches

November 0.15 inch per day; 3 inches

December 0.1 inch per day; 2 inches

Watering a Mixed Landscape

First of all don't. Mixed landscapes of trees and grass are difficult to water.... physically. Second, trees are better off NOT growing in grass. Their roots are better off and their roots will grow deeper. When trees are NOT in a mixed landscape, the trees can get the right amount of water and the water can be applied more easily. 

Trees interfere with applying water to grass as well. They get in the way. Whenever possible separate trees and lawns. Trees and lawns should be on separate valves anyway. Water in our area is just going to get saltier and saltier.

Salt accumulation from the irrigation water on pine trees on this golf course slowed the growth of this tree on its lower limbs (about halfway up). The hybrid bermudagrass (growing beneath it) was fine.

Mixed Landscape of Grass and Trees

In a mixed landscape of grass and trees, lawns probably uses about 6 to 7 feet of water (a bit less due to shade and cooler temperatures of grass) on top of the pine water use. It depends on the temperature, sunlight, wind and humidity it receives but having two plants receiving water for the same area, although not additive, does make for higher water use than either plant alone. 

Mixed landscape in southern Nevada.

Grass in full sunlight uses 7 to 8 feet of water. Pine trees use perhaps 4 to 5 feet more water if pine trees alone are  grown in the same area (grown in bare soil or mulch). Grass is cooler than bare soil in the summer so water use will go up when it is removed (to maybe 6+ feet) but still not as much as needed by the grass alone (8 to 9 feet). Water use of plants in mixed landscapes can be like whack-a-mole.

What To Do?

Use fewer and smaller plants to do a similar job.

Follow the ET calendar when watering.

Give more water to bigger plants. Taller plants are watered wider, deeper, and less often.

Privet Thin Canopy and What to Do

Q. What is wrong with this bush or tree? What can I do to make it look healthy?

Not the tree reader is talking about but it does have a "thin" canopy. It is not dense. How to thicken it? More water and applied to a wider area and add fertilizer once a year. If it is yellow like this, add chelated iron (I prefer iron EDDHA) to the fertilizer in very early spring. It may need compost added to the soil top as well.

A. What I am seeing is a thin canopy and some leaves that have brown tips (leaf scorch). I think this is a ligustrum or privet. When I see a thin canopy, it usually means the soil has “run out’ of organics. Rake the rock on top of the soil back about two feet in all directions and apply a thin layer of compost. This compost will “dissolve” into the soil with water and increase the “organics”. Japanese privet in particular has a difficult time holding leaves when grass is removed.

Leaf scorch or tip burn revealing the plant is not getting enough water, it is planted in a place that is too hot, or plant nutrition is bad. Increase the water to the plant, consider moving it to a new spot, or improve its nutrition with fertilizers or compost or both.

            This time of year (beginning of October) we are transitioning from watering three times a week to two times a week. Each application should be about 5 to ten gallons of water applied to this area via three to four emitters. This can be calculated with the number of minutes you are applying water combined with the size and number of drip emitters. To change the amount of water, do not alter the minutes but instead increase the size of the emitters, or increase number of drip emitters.

            The other option is to replace the surface rock with a layer of fine woodchips over this same area. For faster results apply a thin layer of compost to the soil surface and water it in. Then cover this area with woodchips.