Xtremehorticulture

Xtremehorticulture of the Desert

Sick Oak Tree and Its Spring Recovery

Leave a Comment / Oak tree, rock mulch, sunburn /

Q. I have a sick oak tree in our backyard. It is an older tree and but not growing well. Our gardener suggested hiring an arborist to treat the tree and help it recover. Can we purchase something to correct this? Would an arborist be able to save it? Your thoughts. Sick Oak tree trunk in the backyard. ‘Heritage’ live oak is a good tree choice for two-story homes in Las Vegas. A. From the picture you sent it looks like a southern live oak such as ‘Heritage’. It looks like the trunk of the tree is slow to recover and has some pretty old wounds. Getting it to recover depends on how far “gone” it is. You will not know that until the summer hits. Even though it’s a 30 to 40 foot tree (size-wise think of it as a bit larger than European olive). This particular oak is classified in between xeric and mesic and a native to southern Texas and into the Chihuahuan desert. It does well where there is a bit more water and also into the drier locations. The “cons” of this tree        All oaks like amended soil and don’t like the soil “mineralized” by rock mulch over time. Rake the rock back three feet from the trunk. Change this area over to a layer of organics that can rot on top of the soil. Add a thin layer of finely screened compost to the soil. Water the tree two feet deep once a week right now. This can be done with a sprinkler on the end of a hose. This may be increased to twice a week if it gets hot and windy.             Oaks in general dont like rock up to the trunk but prefer growing in soils getting organics periodically. Rocks cause the soil to become “mineralized” over time (organics in the soil are lost to decomposition). This is the reason for adding compost and wood chips to the top of the soil. Tree roots require deeper irrigation. The bigger the plant, the deeper the roots. Use a length of rebar to judge how to deep to water. To get water deeper with the same amount of time, add more drip emitters!             Secondly, this tree needs additional water each time its irrigated; 15 to 20 gallons during the first few years but now may be 30 to 40 gallons each time. Instead of increasing or decreasing the minutes, add more and larger drip emitters to the area under the tree. Put sprinkler hose water into a 6 to 8 foot wide area under the tree for about one hour and encourage the roots to “chase” the water into this newly wetted area. This will increase the trees vigor and cause it to heal fast. No need for additional fertilizer if the compost is rich with nutrients.             If you see evidence of borer activity from previous years, it probably was reinfested each year since that time. Soil drench the area under the tree with a borer systemic insecticide. Apply it as a soil drench after the tree finishes flowering.

Sick Oak Tree and Its Spring Recovery Read More »

Privet Tree Leaves Black Spots are Disease? No.

Leave a Comment / desert landscaping, leaf disease, leaf drop, leaf spots, Ligustrum japonicum, rock mulch /

Q. I’m sending you a photo of a leaf from my privet tree that has some kind of fungus. Can you suggest some fungicide for me to use? Spotting on privet leaves. It could be a disease problem but it would most likely not be there if the tree was getting proper care. A. I think it is just a lack of good nutrition and perhaps a lack of adequate watering rather than a disease caused by a pathogen like a fungus. Even if it were a fungus disease, it is more susceptible to disease if it is in poor health. However, too much irrigation water applied too often can look similar to this.             Not enough water usually results in leaf drop in the early stages of stress with this tree. I will post your picture on my blog for readers to see your particular problem.             Japanese privet does much better in mixed landscapes rather than alone in rock mulch, if you have it in rock mulch. They do not like soils that develop in a rock environment and have trouble picking up the right nutrients from these types of soils to stay healthy. Please be aware that this tree is not a desert plant so it will require more care to keep it looking good. EDDHA found in the ingredients of an iron chelate fertilizer             Without soil improvement you might try giving it a better fertilizer product. Fertilizers for trees and shrubs from manufacturers such as Miracle Gro, Peters, Jobe’s fertilizer spikes and others will provide better nutrition for the plant than using an inexpensive agricultural fertilizer. Add to this an iron product that contains the EDDHA chelate (look at the ingredients).             Specialty fertilizers like these are not inexpensive. However you can save some money by not using it each time you fertilize. You can make an application and then boost plant performance by using just a little bit of nitrogen fertilizer when the plant needs it.             But if the plant is in rock landscape you will need at least one expensive fertilizer treatment annually to improve your plant performance under the poor soil conditions of rock mulch landscapes.

Privet Tree Leaves Black Spots are Disease? No. Read More »

Depth of Rock or Wood Mulch Depends on the Size of Mulch

Leave a Comment / rock mulch /

Q. I have been replacing gravel with wood mulch and I have to put the gravel someplace. What thickness of gravel can I place around the plants, none at the trunk, without causing damage?  Also, what is the maximum amount of wood mulch can be place around plants without being detrimental to the plant? A. The depth of rock mulch depends on the size of the rock; the larger the rock used the deeper rock mulch can be applied. Roots need to “breathe” so there must be an exchange of gases between the roots and the air. This happens through the pore spaces in the soil. Rock of a larger size can be used as mulch and applied more deeply than smaller rock             Generally speaking, rock mulch is applied somewhere between 2 to 4 inches deep. If this rock mulch contains “minus” material (e.g., 1/2 inch minus, ¼ inch minus) then apply 2 to 3 inches. If the rock mulch does not contain minus material then apply it 4 inches or more.             Course mulch without minus material can be applied right up to the trunk. Rock mulch with minus material should not.             Most information out there tells us not to apply more than 3 to 4 inches of wood chip mulch around trees and shrubs. Where this recommended depth came from I don’t know but it is repeated over and over.             I have no problems applying 6 inches of wood chip mulch or more around trees and shrubs provided this mulch is kept away from the trunk of the plant a distance of 12 inches during its first four or five years of growth. 

Depth of Rock or Wood Mulch Depends on the Size of Mulch Read More »

Converting to Desert Landscapes Can Damage Existing Trees

2 Comments / desert landscaping, irrigation of trees and shrubs, retrofitting landscape, rock mulch, xeriscape /

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.

Converting to Desert Landscapes Can Damage Existing Trees Read More »

Rose Leaf Scorch Probably a Soil Problem

Leave a Comment / leaf scorch, rock mulch /

Q. I have some roses doing poorly. Any thoughts? A. If I see it correctly, it looks like rock mulch in the background. No, no, no for roses. This leaf is showing leaf scorch and marginal tip dieback, a sign of fertilizer, soil and water conditions. They are all inter-related. The first thing we need to consider is soil improvement. In our desert soils they need massive amounts of organic material to bring it up to the bare minimum of 3 to 5 % organic matter for plants like roses. Our soils in Las Vegas are typically around 1/10th of 1% organic matter. Organic matter breaks down over time so to accomplish a 1% change will mean about a 25% volume of compost added to the soil at the time of planting. Surface mulches made of wood mulch like the kind made from chipping trees will contribute organic matter back to the soil and replenish what is lost over time. Bark mulch will not contribute much of anything. It is decorative only. Water should be about two to five gallons at each watering. Watering frequency with surface mulch is about three to four times per week, basically every other day. In the winter this might be every ten days. Fertilizers should be one that promotes flowering, adequate in phosphorus, and balanced with all three numbers present. The first number, nitrogen, should be a relatively high in number. Potassium, the third number would be anywhere from half the value of the first number all the way up to an equivalent number. This would be applied in January or just before or during when new growth commences. Iron chelates should be applied at the same time. Small amounts of fertilizer can be applied every four to six weeks if these are for show. Rosarians suggest the application of magnesium in the form of epsom salt.

Rose Leaf Scorch Probably a Soil Problem Read More »

Roses Growing Weaker After Installing Rock Mulch

Leave a Comment / EDDHA, fertilzing roses, miracle gro, rock mulch, roses /

Q. I have some well-established rose bushes (15 years) in our front yard. Five years ago we converted to desert landscape and the landscaper put about 3 inches of small rock in the area containing the roses. They seem to be healthy although the density and beauty of the blooms was weaker last year.             I’ve been using liquid Miracle Gro. Is there a better liquid fertilizer, or should I consider pulling the rock away from the bases and fertilize through the soil. Thanks.   Not the readers rose but what can happen to roses over time growing in rock mulch and little care. A. Miracle Gro products are fine but I would also add a separate iron fertilizer. Go to your local nursery and get a one pound canister of iron EDDHA. Follow the label directions but I find it more effective to mix in a teaspoon of the product in a gallon of water and water it into the rootzone of each plant. Some of the Miracle Gro specialty fertilizers. Actually any of these would interchangeable. Miracle Gro might disagree but these labels are mostly to help novice gardeners select a fertilizer for specific plants.             Each rose should get maybe one teaspoon January – March, a once a year feeding. Although best applied early, an application will work now. They should be all right if you keep it on this fertilizer schedule. Select a product that has a big middle number. There are several different ones to pick from and I don’t know their product line off the top of my head. This is the correct iron chelate to use in our high pH soils.             Feed roses about every two months lightly starting January – October. However the iron is needed just once a year. Do not neglect soil improvement as well by using composts and organic mulches that decompose into the soil. Roses will really appreciate wood mulch much more than rock mulch.

Roses Growing Weaker After Installing Rock Mulch Read More »

Kumquat Yellowing in Landscape Planting

Leave a Comment / iron chlorosis, rock mulch, yellow leaves, yellow plants /

Q. Here is one of two kumquat trees that I am trying to grow. As you can see it is not working.  I feed and water them what is the problem? Can you help?  Or should I discard?   A. The issues on the other picture could be related to a mineral fertilizer problem. This one could be the same but with the leaves gone it is hard to tell. It also might be related to whatever soil amendments you put in the ground when you planted the trees. But I am pretty confident it has to do with the soil, fertilizer issue or irrigation. It does not help much that they are surrounded by rock mulch. Let’s handle one at a time. Make sure the tree was planted in your soil at the same depth it was in the container. If there was some extreme cold weather, it might also be cold weather damage if you did not see this before it got real cold. Irrigation. Irrigations should be generous but not frequent. A tree that small can get by with ten gallons of water at each application. If these are on drip emitters you should have enough emitters or run the minutes long enough to deliver ten gallons at this size in its life. This time of the year once a week is often enough. When you start to see new growth, bump it up to twice a week with the same volume of water each time. Fertilizer. Go down to Plant World Nursery on Charleston (they are the only nursery I know of in town that carries this) and buy a one pound container of iron chelate fertilizer. If you ask for Doug, Brian or any of the main staff they will direct you to the right one since I recommend it a lot. They even have my name on the label now so people will believe them when they direct them to this product.   For each tree mix about two or three tbs in a one gallon container, stir it and distribute it around the base of the tree where the drip emitters are. Water it in with another gallon since it is sensitive to light. Get some rose fertilizer (like Miracle Gro type) and use it on the kumquat or get some fruit tree fertilizer stakes and put the fertilizer under the rocks or drive two stakes close to the emitters. I think the Miracle Gro is better. Fertilizers are salts. Keep all fertilizers at least 12 inches from the trunk when applied. Mulch. If this were me, I would pull the rock mulch back a couple of feet and put down some good compost (don’t buy cheap stuff) and lightly dig it around the trees from the trunk to a distance of about two feet from the trunk. I would cover the area around the tree in wood mulch but not bark. Keep wood mulch six inches away from the trunk so that it does not cause the trunk to rot if it gets wet. Older trees it doesn’t matter. Lets see if this works for you.

Kumquat Yellowing in Landscape Planting Read More »

Rock Mulches Not Bad But Present Problems for Wrong Plants

1 Comment / dying, rock mulch, yellow /

Rose growing in rock mulch. Q. I have moved into a house that is about 3 years old with a wide variety of plants.  I have read your articles against rock mulch but I don’t know which of my plants can tolerate the rock mulch that is already there and which ones I should pull the rock away and use wood mulch.             I come from Northern Utah and do not have a clue how to handle these types of plants and all this rock. A. I am not against rock mulch but it should not be used for everything and not all plants should be planted into rock mulch.  My personal philosophy on desert landscapes focuses on using appropriate mulches for plants which can tolerate those mulches.              Generally speaking, those plants which originate from arid or desert environments can generally handle rock mulches.  Those plants which do not originate from arid or desert climates probably should not be planted in rock mulch.  There are always exceptions which never help when you are trying to make rules. Photinia growing in rock mulch.             The problem is that we intermingle desert plants with non-desert plants and then we use rock mulch around everything.  Those plants which can tolerate the rock mulch end up, over time, to do all right.              Those plants which are not true desert plants tend to decline and fail over time.  Plants such as bottle brush, photinia, Carolina cherry laurel, Japanese blueberry, butterfly iris, mock orange, and others usually begin to decline in 4 to 5 years after they are planted as soil amendments used at planting are depleted.              If you want to learn how to handle nondesert plants in rock mulches please visit my blog and search this topic. Bottlebrush growing in rock mulch.             The other reason for decline would be improper watering.  Make sure you get your irrigation intervals and the amount that you apply each time to be adequate for the plants.  Improper watering will cause plants to look terrible as well.

Rock Mulches Not Bad But Present Problems for Wrong Plants Read More »

Roses in the Hot Desert Do Well But Different From Growing in New Jersey

Leave a Comment / dying, iron chelate, Las Vegas, rock mulch /

Garden rose not doing well in our desert soils. They can do VERY well if you just follow some simple advice Q. This past spring I cleared a large “L” shaped area in my yard and planted 8 various rosebushes. They have sun from about 9 a.m. to about 5 p.m. They are watered in the evening and fed regularly. They are well planted with planting medium in large holes, and then mulched. All flowered during the spring and early summer. Now, however, they are very spindly looking. The leaves left on them are brown and the stems are turning brown. There are no bugs that I can see. I tugged on them and they are still firm in the ground. Have they died and should I replace them, or wait until spring and see what comes back? Should I cut them back, and if so, how much? I do not want to cut too much off. Leaf scorch on rose due to lack of soil improvement, no organic mulches used and not using an iron chelate as part of your fertilizer program A. Roses will grow best in an eastern exposure with protection from late afternoon sun. They can grow in full sun but they will be best grown in the exposure I mentioned. It is important to use a good compost mixed in the planting soil at the time of planting as well as a starter fertilizer high in phosphorus. Make sure your plants were planted the same depth as in the container or in the nursery if bare root. Make sure the bud union or dog leg on the stem is above ground and not buried. Make sure you stake the rose bush at the time of planting. The stake should not move if you do it correctly. I use a two foot piece of 3/8 inch rebar and tie the rose stem tightly to the rebar with green nursery tape and remove it after one growing season. Roses do well on drip irrigation. Use two emitters per plant or you can use drip pipe with inline emitters such as Netafim, Geoflow or equivalent product. If on drip it is important to note the amount of water the emitters deliver per hour and adjust your time on the emitters so that each plant gets about two to three gallons every time they are irrigated. Irrigations should be about two to possibly three times per week this time of year. Less often as it gets cooler but the length of time or hours should remain the same. Roses doing quite well in our hot desert climate and poor soils It is best to use a wood mulch rather than a rock mulch. All mulches must be pulled away from the rose stems at least 6 inches at the time of planting or the roses can get crown rot on the stem and die. Fertilize roses once in January with a rose fertilizer plus a soil applied iron chelate containing EDDHA. Follow label directions. You can fertilize again lightly after the heat of the summer has passed to help stimulate fall rose production. This should get you going. My guess is that they may have been planted too deep or the mulch touching the rose stems may have caused collar rot or irrigations may have been inadequate; either too often or not enough water. Just a hunch.

Roses in the Hot Desert Do Well But Different From Growing in New Jersey Read More »