Roots of Trees Follow the Water in the Desert

Q. You posted pictures about watering with the depth of a plants root system. How do trees survive in lawns then?

Suggested root depth of different plants and how much water to give them. This makes it easier to see that taller plants have deeper roots and need to be watered as such. As the roots get deeper they also get wider. This is why big trees use more water than little trees.  https://wateruseitwisely.com/saving-water-outdoors/plant-watering-guide/

A. Some trees survive in lawns and others don’t. As a rule of thumb, mesic (nondesert) trees will survive in lawns while xeric (desert) trees will not. For instance, ash trees (mesic) will survive in a lawn. Xeric (desert) trees will die if they receive water too often. Xeric trees such as Foothills Palo Verde will struggle in a lawn. Mesic trees are better suited for lawn areas than xeric trees.

Roots of trees will go where there is plenty of water even if it's in you or your neighbor's yard. It goes without saying that large trees should not be planted close to walls.

Plants are lazy, including their roots. Roots grow best where can get water mixed with air and get it the easiest. That concept pertains to both mesic and xeric trees. Daily watering during the summer means the roots of (mostly) mesic trees growing in a lawn area will have roots all through the soil surface. There they can get a mixture of both air and water the easiest.

Roots growing in lawns well head to the surface of the lawn because that's where they find a good mixture of air, water, and fertilizer.

Removing the lawn also removes this distribution of water and air. Instead, these trees must survive on the water provided through drip emitters. That is a change from watering the lawn to watering shrubs. Is that enough water? Is the water provided in the right distribution? Is the water provided to the tree in the right spots? You will find out usually next summer when it gets hot. By the way, surface mulch (rock or wood chips) helps stop the water from evaporating from the soil during the heat of the day.

Golf course superintendents well water new trees with a water truck even if they're growing in grass.

Besides water, roots of tall pine trees provide stability for the tree during wind. A general rule of thumb is to water deeply according to its height. For instance, tall trees growing without a lawn should be watered to a depth of 3 feet to provide the tree stability during windy weather.

How to Get Rid of Snails in a Lawn

Q. I have some snails in my lawn. How do I get rid of them?

Snails like it wet and darker than most lawns.

A. The best way to control snails (or slugs) in lawns is to give the lawn more light. Snails hate light but they like to eat!  Snails and slugs eat young plants and microscopic plants such as “large enough to see” algae.

The worst situation for snails and slugs is lawns growing under trees producing shade. The bigger and denser the tree gets, the more shade it produces.

Dappled shade produced by the branches of trees may need to be thinned if it gets too dense. Snails and slugs hate sunlight, prefer shade, and wet soil. Right now there is enough light for the lawn as well as snails and slugs....if the lawn is kept wet.

In cases like that, get rid of the lawn, or both, but in the desert never favor the lawn over the tree. A good-looking fescue lawn uses a lot more water than nearly any tree and usually requires daily applications of water in the summer. Fescue lawns in the shade of a tree might still need 6 or more feet of water annually to look good. Many of our trees in full sun will need anywhere from two to 5 feet of water applied under their canopy. Xeric trees like acacia need less water, annually, than mesic trees like pistache or vitex.

Snails and slugs in lawns

There are baits made for snails and slugs. Those baits usually contain iron phosphate which is low in human toxicity. But it is a pesticide.

Sluggo is the old tried and true chemical control for snails and slugs.

If you are into organics, then you might not want to use Sluggo. Your only options are to increase the light and trapping. During times of high light levels snails and slugs look for places to “hide” so laying out boards or other places so they can hide during the day provide places where they “collect”. Their numbers can be reduced if you are willing to dispose of them after they collect during the day such as under something.

Low Water Use Plants Need Water in the Desert

Q. Over a year ago our city planned a new extension to a community Park and put in a dirt trail surrounded by “native plants”. They dug wells and put in an assortment of plants and trees with no water source. The first month they used a fire hose from the hydrant to water the plants. Since then, nothing. I counted over 185 dead plants this morning. My question to you is there certain plants for that zone or location that will be able to survive without any water?

Cleveland sage is best planted on the east and north sides of a building. It comes from the Baja and coastal California where it grows best in a Mediterranean climate.  Water to get it established and then not more often than about every two or three weeks.

A. Not really, no. Even cacti occasionally need water to get established and grow after planting. Cold hardy desert plants are best planted in the fall; winter tender plants in the spring. In very dry summers, desert plants will need supplemental water once a month or more during the summer to look good and survive. Cities and homeowners are not Mother Nature. Even so-called desert plants need water occasionally (and usually some soil improvement) periodically/regularly/deeply to look their best. Homeowners won’t tolerate plants that look bad.

Opuntia, or bunny ears cactus, are native to all over the desert southwest including the Mojave desert. To get growth water them about every three weeks in the summer.

            For each plant that makes it in the desert after a rain, thousands of plants don’t. The advantage of desert plants is their ability to survive periods of time without water. To think we can guess where plants will survive after planting is pure arrogance. Desert plants respond to water. They respond best when the water is applied to the same spot. They respond by growing.

Texas sage or ranger (the barometer plant) hates, hates, hates to be trimmed by a hedge shears unless its growing as a hedge. This is what happens. Water it about once every two or three weeks or when the leaves start to drop.

            Some, like Texas ranger (the barometer plant of the Chihuahuan desert) produce flowers on new growth after a rain. As these desert plants get drier, they first drop their leaves (if they have any). Even cacti will put on some new growth after a rain and may even flower!

Winter/Spring Flowering Plants to Attract Bees

Q. I’ve been trying to attract bees to my garden and thinking about a hive at some point. Need to put in some year-round flowering plants first. Rosemary comes to mind. Any thoughts or literature that comes to mind.

Rosemary flowers during the winter and spring when honeybees are active and looking for open flowers.

A. Rosemary is a good choice; it flowers during the winter and is lower in water use since it is a Mediterranean plant that is smaller. Any plant that has conspicuous flowers during early spring and is cold hardy will work. That is one reason roses work so well. Other plants to consider that flower during that time and are cold hardy for our climate include the different Texas sage and Tecoma types.

Tecoma stans and Texas ranger also flower during the winter or spring.

Don’t forget a mixture of annuals and perennials that have brightly colored flowers. Use many different colored flowers like mustards, clovers, desert bluebells and blue eyes, and the like. Scratch the seed into the soil with a rake and start watering them twice a month in December and January with 15 minutes of water from a sprinkler. Turn off the water when your fruit starts flowering.

Flowering mustards, many are winter annuals that flower during the late winter.

Don’t forget water. Honeybees like to haul water during the winter as the hive starts to warm up. Bird baths and plastic troughs dug in the ground help attract bees and other critters. Don’t let the bees drown. Put rocks in the water so bees have a place to land. Honeybees are active during the daylight anytime temperatures are in the mid-50s, clear and sunny and little to no wind. Night flowering plants such as some cacti don’t work because bees need to see the sun to fly. Honeybees are supplemented with sugar water when they can’t find flowers they like. Feeding the colony with sugar water helps to keep the population alive during the coldest parts of winter.

Honeybees like to haul water in the summer to cool the hive. Give them a chance by putting some stones in the water and give them clean water to use.

Attracting Honeybees into a Garden Landscape

Q. I’ve been trying to attract bees to my garden and thinking about a hive at some point. Need to put in some year-round flowering plants first. Rosemary comes to mind. Any thoughts or literature that comes to mind.

Rosemary flowers in the winter so it is a good choice for attracting and feeding honeybees to keep the hive alive.

A. Rosemary is a good choice; it flowers during the winter and is lower in water use since it is a Mediterranean plant that is smaller. Any plant that has conspicuous flowers during early spring and is cold hardy will work. That is one reason roses work so well. Other plants to consider that flower during that time and are cold hardy for our climate include the different Texas sage and Tecoma types.

Texas ranger (sage) flowers during the winter and is a good choice for attracting and feeding honeybees.

Don’t forget a mixture of annuals and perennials that have brightly colored flowers. Use many different colored flowers like mustards, clovers, desert bluebells and blue eyes, and the like. Scratch the seed into the soil with a rake and start watering them twice a month in December and January with 15 minutes of water from a sprinkler. Turn off the water when your fruit starts flowering.

Honeybees haul water if its in the garden.

Don’t forget water. Honeybees like to haul water during the winter as the hive starts to warm up. Bird baths and plastic troughs dug in the ground help attract bees and other critters. Don’t let the bees drown. Put rocks in the water so bees have a place to land. Honeybees are active during the daylight anytime temperatures are in the mid-50s, clear and sunny and little to no wind. Night flowering plants such as some cacti don’t work because bees need to see the sun to fly. Honeybees are supplemented with sugar water when they can’t find flowers they like. Feeding the colony with sugar water helps to keep the population alive during the coldest parts of winter.

Pine Trees Don't Need as Much Fertilizer as Fruit Trees

 

Pine trees in the desert do not need as much fertilizer as fruit trees. We don't expect as much from them as we do fruit trees.

Q. I have a few Aleppo pine trees that I fertilize and water regularly growing in Logandale. I am wondering how much fertilizer to give them each year and how much to water them. I am wondering if I can get them off of the irrigation due to a shallow water table here and apply less fertilizer.

Pine trees access water from shallow aquifers if they are within a few feet of the surface of the soil. One way to see if that is the case is to look for salt pushed to the soil surface by shallow water.

A. In my experience trees like Aleppo pine need fertilizer applied AT THE MOST once a year and perhaps less often. In the case of pine trees mostly nitrogen and potassium because we don’t need them to flower or fruit. That requires fertilizer higher in phosphorus, the middle number. Whenever the trees are “improved” (hybridized or improved for some reason) they need to be fertilized more often and need more care. For example, most fruit trees require one full or a split application of fertilizer twice a year.

This is Burgundy plum growing in Las Vegas, NV. Fruit trees will need more fertilizer if we want large fruit to be produced. Are expectations aren't as high for pine trees so they can get by without applying as much fertilizer.

My guess is that your pine trees, at the most, will need fertilizer applied once a year in the spring. Improved trees like fruit trees need about one pound of a nitrogen fertilizer in the spring (or the fertilizer divided in half and applied twice) for each 1000 square feet under their canopy. Aleppo pine trees require it less often or apply less total amount each time you fertilize.

New growth of older pine trees should be at least 8 inches or more to give adequate growth for a full canopy.

Look at the results of irrigations and applications of fertilizer. The fertilizer is needed every year or every other year. A tree of that size should put on about 8 inches of new growth every year to keep it full. That takes primarily nitrogen similar to a lawn fertilizer (21-7-14). Don’t skimp on nitrogen and potassium in the fertilizer for pine trees. Because they are “all green” and no flowers or fruit you can apply less of the middle number (the amount of phosphorus).

As far as applying irrigation less often or eliminating them, you need shallow groundwater to about 5 to 7 feet deep. At the same time force its roots to grow deeper in the soil so it can discover the water. Pine trees have taproots or large roots that can grow deep if given the chance. Groundwater can go down in the summer months and up to normal in the winter. What I am telling you is that you might need to water occasionally during the summer months.

This is bubbler and basin irrigation on pine trees. The basin doesn't have to be deep but it must be flat and capture the water from the bubbler so it stays put long enough and penetrates the soil deeply.

When you irrigate, water the trees deep when you do, water them less often and watch the tops. Force the tree roots “to go after” deeper water and see how much fewer extra irrigations they need and still maintain 8 inches of new growth during the early summer months.

Pines in Logandale Need Less Fertilizer But the Same Amount of Water

In my experience trees like Aleppo pine need fertilizer applied AT THE MOST once a year and perhaps less often. 

Non-Flowering and Non-Fruiting Trees Need Mostly Nitrogen and Potassium

In the case of pine trees mostly nitrogen and potassium because we don’t need them to flower or fruit. That requires fertilizer higher in phosphorus, the middle number. Whenever the trees are “improved” (hybridized or improved for some reason) they need to be fertilized more often and need more care. For example, most fruit trees require one full or a split application of fertilizer twice a year.

Force Them After this Water

My guess is that your pine trees, at the most, will need fertilizer applied once a year in the spring. Improved trees like fruit trees need about one pound of a nitrogen fertilizer in the spring (or the fertilizer divided in half and applied twice) for each 1000 square feet under their canopy. Aleppo pine trees require it less often or apply less total amount each time you fertilize.

Look at the results of irrigations and applications of fertilizer. The fertilizer is needed every year or every other year. A tree of that size should put on about 8 inches of new growth every year to keep it full. That takes primarily nitrogen similar to a lawn fertilizer (21-7-14). Don’t skimp on nitrogen and potassium in the fertilizer for pine trees. Because they are “all green” and no flowers or fruit you can apply less of the middle number (the amount of phosphorus).

As far as applying irrigation less often or eliminating them, you need shallow groundwater to about 5 to 7 feet deep. At the same time force its roots to grow deeper in the soil so it can discover the water. Pine trees have taproots or large roots that can grow deep if given the chance. Groundwater can go down in the summer months and up to normal in the winter. What I am telling you is that you might need to water occasionally during the summer months.

When you irrigate, water the trees deep when you do, water them less often and watch the tops. Force the tree roots “to go after” deeper water and see how much fewer extra irrigations they need and still maintain 8 inches of new growth during the early summer months.

Pines and Eucalyptus With no Water Growing in the Desert

Q. I have pines and eucalyptus that are not being irrigated at all. There is no irrigation applied but these trees are tall and healthy. What gives?

This eucalyptus has on applied irrigation in the desert. Sometimes trees can access underground water and survive.

A. Trees need water to survive. And large trees need more water than smaller ones. Some trees like your eucalyptus and many pines can grow deep roots. But trees need a minimum amount of water, or they won’t thrive otherwise deserts would be filled with tall, healthy trees like yours. They are getting water from somewhere.

Large trees use more water than smaller trees. Such is the case when the water was turned off to this mulberry.

           Plants are lazy, like us. Tree roots take up water where its easiest to survive. If they want to reproduce, then they need more than enough to survive. If the deep water is easiest to follow, then it will use it, if their roots can reach it.

           Tree roots don’t “seek” water in dry soil. They chase it. They “sense” water is there (compared to dry soil surrounding their roots) and grow best where water (and air) are abundant. If it can get lots of shallow water, like growing in a lawn, then that’s where tree roots grow abundantly as long as they can get air as well. If the water is deep, then that’s where roots grow if the soil is moist often enough to attract tree roots and they can “breathe”.

           Established pine trees grew “without water” at the El Rancho on the Las Vegas Strip after its fire. The property was abandoned, and the irrigation was turned off as well. Pine trees had to survive on only the deep salty water that their roots could get several feet below the Strip. This available water used to be considered a “nuisance” until developers saw its value in the desert. As Mark Twain used to say, “Whiskey is for drinking; water is for fighting over.”

           Both established pine trees and many eucalyptus have the potential to develop deep roots if given a chance and find a deep source of water.

Cure Yellowing Eucalyptus Tree

Q. I have a 20 plus year old eucalyptus tree. The leaves are very yellow. What is the cause of this?

Its not a simple answer when it comes to yellowing eucalyptus. Could be anything. Judging from the plants around it and recent water restrictions I am wondering if it is water related.

A. Yellowing leaves can mean many things. It could be a nutritional problem, watering issues, or damage from insects or disease. I need more information as well as leaf and tree pictures. Make sure it gets an iron application to the soil in the spring. To be on the safe side, apply an iron chelate such as EDDHA.

This is the iron chelate called iron EDDHA. Because of its chemistry it performs well in all soil pH if applied in the spring.

            Check for a watering issue or a leak that floods the soil in that area. Eucalyptus is “mesic” in their water use so an application frequency for large trees should be used. When water is applied it should be deep and wide or large shrubs that receive water should be located under its canopy. Once a tree is chosen its increasing water use as it gets bigger has also been chosen.

Figs an an Oasis Tree. They Need Water When Producing Fruit

Q. I planted various fig trees that were very good producers in southern California, Los Angeles County to be exact. Here they have been planted for over 10 years and I have yet to pick and eat any fruit from any of the trees! The problem that I am experiencing is fruit drop off. The figs grow to a fifty-cent piece and then they drop off.

Figs need water when they produce fruit even if the tree looks fine.

A. At the University Orchard and elsewhere I grew nearly 12 varieties of figs, and all have done very well. As long as they get enough water. Figs are what I call an “oasis” fruit tree. They handle the heat and do well and produce fruit if water is available.

Hot, Then Water More Often

            However, this is the desert. Our desert has two major problems when growing fruit trees like figs: soil improvement and water. Figs produce basically two crops of fruit. These are classed as the “briba” crop and “main” crop. The briba crop is the earliest because it produces figs on last year’s growth. This is also the crop that fails each year if there is a late spring freeze.

Figs produce fruit in different stages. First is the early or 'Briba' crop. The second crop of figs are produced on growth from this year and called the 'Main' crop.

            But figs also produce a “second” crop later in the year called the main crop. This main crop of fruit starts growing late enough in the season that freezing weather has gone. It starts to produce figs early in the season when it starts getting hot. It gets hotter so the tree needs more water to produce its figs. It is confusing because the tree shows no signs it needs water because the leaves look fine! But the figs drop off because the tree needs water. Very confusing!

            Those are the keys to successful fig production. Give it a productive soil and apply a two-to-three-inch layer of surface mulch.  Water it more often in the early summer even though the tree doesn’t look like it needs it.

Loss of Pine Limbs May Be Light or Water

Q. I have a large pine tree in a natural area losing limbs from the bottom up. It’s needles are browning and dropping. I don't water the tree much at all, but I have a water channel flowing 3 feet away on one side of the tree. The channel is mostly filled with moving water and is about 1 foot wide.

A. It's probably either water or light issue. Not enough light because trees are planted too close together will also cause lower limbs to die and drop. Sometimes light is not considered.  Pine trees planted four to six feet apart are too close together and lower limbs will die as they age.

An open canopy pine tree signaling that maybe the tree was either not receiving enough water OR it cannot get the applied water to the needles due to trunk damage.

            My guess is that it's water related; not enough. An easy way to find out is to put a sprinkler on the end of a hose and give the tree one to two hours of water once every three weeks to a month. I would use a non-oscillating sprinkler and adjust it to about 8 feet wide. Use a four foot long piece of rebar to adjust how many minutes to water.

Hose-end sprinkler.

            There are two ways that I use to tell if a pine tree isn’t getting enough water; 1) I look at the amount of new growth and 2) its canopy density. On well-watered, fertilized smaller pine trees to about 20 feet tall, I like to see about 18 inches of new growth and a solid canopy density. On older well-watered pine trees 40 to 60 feet tall the growth will be a lesser amount, perhaps 8 to 12 inches, but the trees still have a dense canopy.

If growth is 2 to 4 inches when the pine tree is older then growth is not enough. Measure growth at the end of May after spring growth is finished.

            Pine trees with drought problems usually grow 2 to 4 inches in length each year. This small amount of growth translates into a very open canopy. Because pine trees can have other problems as well such as borers and woodpeckers (sapsuckers), I inspect the trunk for this kind of damage as well. A tree trunk with extensive damage by borers or woodpeckers may also show signs of drought. Pine trees with only a few inches of new growth each year and an open canopy usually suggests drought.

Tomatoes With Black Bottoms Now Being Seen

Those of you who were lucky enough to get your tomatoes planted the first part of March have already tasted your home grown tomatoes. Quite a few of you have discovered tomatoes with black bottoms. What do you do?

Ocotillo Watering Should be Infrequent in Desert Landscapes

Q. I have trouble with my Ocotillo.  They get beautiful green leaves that last about two to three weeks and then turn brown and fall off.  They are on my watering system.  Are they getting too much water?

Cat Claw Vine Beautiful in the Desert But Not Elsewhere!

Q. I planted six cat claw vines two summers ago in full sun. They are on a drip system and I hope to wean them from regular water once the area is covered. I believe you mentioned to avoid mulching cat claw vine.  Of course I had already done this and the plants are struggling.

Controlling Growth of Shrubs More Than Water and Fertilizer

Q. You have always have stated to prune shrubs and trees when they are dormant, but it seems mine do not go dormant in the winter.  They continue to grow even though they get water only once a week.  I halved their fertilizer application but they continue to grow larger than I want them to. Why do they grow when they should be dormant and when should I prune them to slow their growth and spread?

A. Shrubs desire to reach their mature size. Keeping them smaller than this will require more maintenance than selecting one that is the size you need. Select shrubs by determining the size you need and finding one that fits that size at maturity.

            Dormancy here is not the same as dormancy in Minnesota. Dormancy here, in some cases for some plants, means that they may stop growing as much, not that they stop growing at all. Just depends on the plant and its location.

            Where the plant is located in the landscape also dictates its level of dormancy. Very warm microclimates in the yard may mean that some plants never totally shut down during the winter while in colder spots they do. Hot south and west facing walls with little winter wind are the warmest locations.

            Cutting back on water and fertilizer will help but they do not act like an “on and off switch” for plants. Think of fertilizer and water more like a “rheostat” where it can increase and decrease growth but not totally shut it down. At some point though, turning down the water and fertilizer will damage the plant. The real solution is to match plant mature size to the site.    

            Focus your pruning on older growth and remove it from deep inside the canopy leaving the younger growth still flourishing. Prune in the winter months. Avoid trimming on the edge of the canopy whenever you can. Hide your cuts if at all possible. They should not be obvious. This will help keep them smaller.