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Tuesday, August 20, 2013

Do You Want to DISCUSS Horticulture in the Desert? Please join.

I created a new Yahoo Group for discussing growing plants in the desert. There is alot of experience out there and recommendations should not come from one source. If you have something to share, or just want to listen in, come join our new Yahoo Group

Click here to pioneer this new discussion group

Who will be the first to post a comment to get things rolling?

Why I Dont Like to do Plant Recommendations

Q. I was wondering what shrubs you would recommend to plant this fall (here in Las Vegas)? I prefer ones that will stay green all year long.

A. I normally don’t recommend specific shrubs for a number of reasons; there are so many, I would have to provide a list of 25 to 50 shrubs and we would go back and forth with questions for you to answer, if I recommend them there is no guarantee you can find them here.

So I would highly recommend some trips to the nurseries, tell them what you are looking for, they will ask you a bunch of questions to narrow the choices, they will recommend five to ten they actually carry and then you can narrow it down to a few you like.

 Then, if you give me the names of the ones you like and you can find locally, I can help you with your decisions with pros and cons. Thanks.

Call Me Looney When it Comes to Drip Emitter and Drip Design


Q. The landscape people are into variable emitters and think I am a little looney sticking to drip emitters.  How do you determine how many gallons to give large trees -- like African sumac, bottle trees, Swan Hill olives, Yew pines and chaste trees?

A. There are three things we have to consider when watering; how much water the plant needs, how frequently it needs it and the time of day when we will apply the water. All this needs to be entered into the irrigation controller. All plants of a similar size will be watered with a similar amount of water.

Larger plants require deeper watering and more applied water
In your example, you have two different categories of trees to consider; the desert trees like bottle tree and chaste tree AND non desert type trees like the African sumac, olives and yew pines. If they are all the same size then they will get a very similar amount of water. The difference in irrigating these two types of trees is the FREQUENCY or how often they are irrigated. True desert trees can be watered less often and should be. The nondesert trees can be watered more often.
If watered too often, many desert trees can have problems. If the soil drains of water freely then the usual problem we see is luxurious, unrestrained growth. Have you ever had a neighbor or friend brag, "My mesquite tree last year grew 8 feet! (i.e., I must be an extremely good gardener if I can get a tree to do that!). Well, my friend, it just means it is getting alot of water. Most desert plants respond to excess water by putting on lots of growth! As these trees get larger and larger, they will demand more and more water.
The smaller plants are easiest to do. I like to ask people, "What size container would you use to grow that plant?" Some people can visualize this while others have a hard time at first. Just think of the plants you see at the nursery. Generally speaking, I like to make sure the plant is getting at least half of the volume of its container to a maximum equal to the size of its container. It is better to estimate too much than not enough.

Different sized nurseery containers
(Disclaimer: nursery containers do not hold their namesake. For instance, a five gallon container DOES NOT hold five gallons. I know its dumb, but use its namesake anyway.)
You will apply all of this water in one hour. So if you need to apply five gallons of water, it will need to be applied in one hour. So the total amount of water applied to the plant would be five gallons per hour.
Then there are the types that are variable and can be twisted open to give you more or fewer gallons per hour. You have to figure make the conversion and convert it yourself. It is not terribly hard to do, particularly in drip irrigation. Each emitter is labeled or color coded to the gallons per hour that they emit

"Flag" type drip emitter. Usually the flag allows you to turn it on or off, you can usually pull it to clean it, and the color refers to how much water it emits per hour. They are very simple to use, clean, inexpenive and accurate. I have used them in simple drip systems with no problems for over 20 years. There are also many others depending on your needs.
The hardest emitters to figure out are the types that can be adjusted to different amounts of water. Many of these are adjustable between 0 (shut off) to 10 gallons per hour. It seems simple. You just twist the emitter open and it delivers more gallons per hour.

I am sorry to you out there that like these emitters. I do not share the same feeling. When I see them, I just cringe. This is a variable output drip emitter that varies from "completely closed" to "I have no idea". Landscapers LOVE them. Of course! It doesnt require any knowledge and no design is needed! Wonderful option for the ignorant.
But in actuality it begins to defeat the purpose of drip emitters: precision. Also many of these variable flow emitters are not pressure compensated. If it is not pressure compensated, then opening one emitter and allowing more gallons to flow can affect the number of gallons flowing on all the other non pressure compensated emitters on the same line. This can mean you have to twist open or twist close each emitter along the same line perhaps multiple times to get the flow that seems to be appropriate.
Not only that but these variable output emitters frequently emit so much water so quickly at the higher settings that it results in water puddling and running off to low spots. This is exactly contrary to the reason we should use drip emitters. So you can see that I am not terribly fond of these types of emitters.

With many different types and sizes of plants along the same line the next difficulty for most people is to figure out what size (gallons per hour) to match up with each plant along the line. So this is how I do that.
The first thing I do is determine how many hours or minutes the valve will be left open for watering. Frequently, for drip irrigation, the shortest time you should use is one hour. "Yikes" you might say because most people want to irrigate fifteen or twenty minutes. The problem with these short irrigation times is that it may force you to use the variable output emitters. Or it results in water applied so rapidly it does not penetrate the ground and instead runs and puddles somewhere it is not supposed to go.
Assume a minimum of one hour for the irrigation time. In some cases you might water for two or three hours on a single line. What difference does it make? You are not standing there with a hose and it can take all night if you want it to. There is no problem watering at night with drip irrigation. Let it soak long, slowly and deeply. Try to use at least two emitters per plant in case one plugs.
Here is the one hour example.
  • One gallon plants, give them one gallon per hour (two, half gallon per hour emitters).
  • Five gallon plants, give them three to five gallons per hour (two, two gallon per hour emitters or three, one gallon per hour emitters).
  • Fifteen gallon plants give them 8 to 15 gallons per hour (two, four gallon per hour emitters or two, five gallon per hour emitters or three, three gallon per hour emitters, etc.)
Distribute the emitters under the plant canopy, one foot from the plant with distribution tubing and secure them in place with rock mulch or stakes to hold them. Emitters should be above the mulch so you can check them for plugging. Plants that are spaced closely together can, and will, get water from each other.

Does this help a bit?

Slow Growth Can Be a Sign of Poor Plant Selection

Q. We notice that some of our trees don't seem to be rooting into the soil properly.  We assume it's due to improper root ball preparation or girdling roots. Our test to see if the tree has rooted after at least one growing season is to bend the tree trunk back and forth.

            If the root ball under the soil easily moves when the tree is pushed, we assume that the tree has poor or little rooting into the surrounding soil.

            We also believe it’s a permanent problem, not correctable and thus the tree needs to be replaced.  Any suggestions for making a better evaluation and discovering this potential problem before planting?

Root circling from container plant

A. Poor tree establishment due to girdling or circling roots is a major problem with many plants, not just trees. This problem can begin at a very early age, even when it is just a seedling. But if plants are grown too long in containers then the problem can become worse.

            Once roots begin growing in circles inside a container the problem can no longer be corrected, even at planting time. This problem should be identified before purchasing and the plant rejected.

Roots seen circling when pulled from container

            Generally speaking, plants which are very large compared to their container have a significant chance of having girdling roots. Buying oversized trees in containers is no bargain.

             When buying a container plant that I can lift, I will gently pull the plant a few inches out of the container and inspect the roots for circling. This includes bedding plants! Secondly, I select trees that are not oversized for their container. Here is a case where smaller plants of the same sized containers will out-perform the larger ones.

Surface roots from circling container roots. Notice how the trunk lacks "flairing" at the soil surface on one side of the tree. One way to detect these types of roots when they are present but hidden below the soil surface.

            Plants in containers should usually root, or become established, in one full growing season. Large trees, such as those planted from boxes, may take two to three seasons. Malformed, girdling roots will continue to circle in the same pattern once they are planted in the ground. Because of this, they will never grow beyond the planting hole after planting.

            In other words, they stand a good chance of never getting established. If they never grow beyond the planting hole, the tree roots will never be strong enough to support the tree when it gets bigger.

Scoring the rootball can sometimes help repair girdling roots, if they are not extensive, when planting. This NOT a substitute for good plant production practices or poor plant selection.

            A sign that a tree may have circling or girdling roots after it has been planted is stunted growth. This stunted growth can take years after planting before it appears. It is a good idea to identify trees that have this problem early in their development.

            Another indicator is the presence of girdling roots on the soil surface and a lack of trunk flaring at the soil surface but this can take years to develop.

            Your method is a good one for determining if trees have not become established after planting. Once the establishment period is over, I use the same procedure that you prescribe (bending the trunk) to determine if there are girdling roots down there or not.

            Boxed trees are replanted from containerized trees. Normally, container trees are staked as soon as they are planted in a box. However, if the container tree had girdling roots then they will continue to girdle and never establish in the box.  

            There are three other things that can cause poor rooting into the surrounding soil as well; poor hole/soil preparation, improper staking or not staking after planting and watering too close to the tree.

Pluot Can Have Sap Oozing Like Both of its Parents

Q. We planted a pluot this past spring along with four peach trees of different varieties. The pluot just started oozing sap or gumming on the lower truck. All of the trees were planted as bare root trees. The trees have a bermed area for holding water with wood chips for mulch. I am watering two to three times a week and frequently check soil moisture around the roots with a very long screw driver.

A. In peach, gumming or sap coming from the trunk or limbs, is frequently due to borers. In both plum and apricot (the parent trees of pluots) gumming can happen without borer problems. Frequently it is a sign of stress.

Sap oozing from trunk even with trunk painted

            Make sure that the trunk and limbs are in the shade of its own canopy to reduce sunburn from direct sunlight. Sunburn damage can cause this as well. Paint the trunk and limbs with diluted white latex paint to reduce sun and heat damage to these areas.

            Dilute white latex paint with an equal amount of water and either spray it or brush it on. This will reduce the surface temperature of these areas about 5 to 6 degrees. We normally do this in the winter when we don’t have to fight with the leaves and after pruning is done.

Buford Holly a Thing of the Past In Las Vegas?

Q. We have two holly trees in our front yard that are at least 40 years old.  Last summer one of the trees began to get curled leaves and this year the entire tree looks like it is dying. The trees are on the north side of our house and get sun in the morning and afternoon. We were told locally that the trees are probably dying from old age but they didn’t know the name of the tree. We had our entire front yard replaced with desert landscaping this spring but that should not have caused the problem because one of the trees began getting curled leaves last year.
Plant problem sent in by Reader

A. Years ago Chinese holly (Ilex cornuta) was commonly planted as a foundation plant in southern Nevada. They performed best planted on the north or east sides of a home, somewhat protected from the hot sun.

            The most commonly planted Ilex was ‘Bufordii’ or Buford Holly. You can google this name in google images and see if it matches your plant. With the onset of desert plants and desert landscaping it has pretty well been forgotten along with some other really cool plants. All the nurseries in Las Vegas carried it forty years ago and many up to about 20 years ago.
Burford Holly Foliage
Buford Holly foliage

            Buford holly is fairly long-lived but I have to agree a bit that as  they age, without proper care, they will begin to decline.
Buford Holly berries (poisonous) from University of Florida website

            I am not sure what the problem is but since one or two limbs are dying back you will most likely see the cause by following those dead limbs back inside the plant until the dying stops. The problem should be at that spot or very close to it.

            A real guess is that it might be a wood boring insect that is common to all plants here. I rather doubt that it is a disease but it is most likely mechanical or physical damage by insects tunneling or accidental damage by a human being.

            Buford holly is a beautiful plant if it is well cared for. It will get to about six feet, taller in very protected areas. It can be grown into a small tree maybe getting as tall as 20 feet. The thick glossy leaves have spines but not nearly as spiny as English holly.

            They will produce more red berries in winter if you have a female plant and there is a male nearby. Sometimes they appear to produce these red berries with no apparent mate nearby. All hollies grow best in rich, slightly acidic soils. They would do nicely grouped with camellias and other sun-tender and acid loving plants.
From residence in East Texas

            Remove this dead limb by cutting it just above the healthy part of the limb. Add another drip emitter or increase the amount of water that is applied and apply a fertilizer such as Miracid or a fertilizer for acid loving plants at least once a year in the spring. Do it now if it has not had any for awhile.

            Applying mulch to the base of the plants will help conserve moisture, add nutrients to the soil, make the soil more acidic, reduce weed problems and improve the general vigor of the plant. It would help to have it pruned carefully by someone who knows how to prune.