Growing the Desert Garden

Welcome to the Desert Garden, with garden coach Tyler Storey, where we talk about everything having to do with gardening and landscaping in the Desert Southwest. From composting to Cercidium and agaves to arugula — we'll cover everything you want to know to grow your own beautiful Desert Garden.

Wednesday, July 23, 2008

From the Inbox: Pruning Paint

From a Correspondent:

I hope you can help.  I have a huge fig tree growing in my backyard. Three of the limbs broke from being too heavy with leaves and fruit. I would like to know if I should apply either pruning paint or tree tar on the limbs that have been cut.  If the cut limbs need some kind of product put on them, could you recommend a product?
Thank you for your help.
Carson, California
Hi Aurora,

While I'm sorry to hear about your breaking fig tree, I do have good news: you don't need any kind of pruning paint or wound dressing.  More than that: you don't want any kind of paint or dressing.  

Trees, for the most part, do a wonderful job of taking care of themselves; the breaking of fruit-laden limbs reminds us that there are exceptions.  When it come to recovering from wounds, though, trees are best left to their own devices.  Pruning paint, sealing tar, and other kinds of wound dressings have been found to do no good in protecting the tree, and it appears that they may actually interfere with the tree's own process. 

Any time we prune a tree, whether to shape it or as a result of accidental damage, as with your fig tree, the tree is wounded and its outer protective covering (the bark) is compromised.  As when a person has a cut, this damage opens up the tree to the possibility of disease or insect damage.  Unlike a human or animal though, a tree doesn't really heal a wound; trees seal their wounds instead.  

The late Dr. Alex Shigo did extensive research which showed that trees undergo a process he called CODIT, an acronym for "compartmentalization of damage in trees."  The short version is that trees seal off their damaged areas from their undamaged areas, and eventually may also recover the outer area of the damage bark with a new layer; if you've ever gone back and looked at a tree you pruned a few years earlier, you have probably seen where the cut is now covered over with new bark.  

What does all this have to do with pruning paint?  I'm glad you asked.  Pruning paint or other wound dressings interfere with the natural sealing process of the tree and can actually prevent it from taking place.  Air exposure, sap weeping, decay organisms and all the other things we hope to "correct" with the use of pruning paint are all critical parts of the tree's sealing process.

Do go ahead and remove the ragged stubs where your fig's branches cracked, but other than that, you'll be best served by leaving the tree to recover on its own.  

Next year you may wish to thin the fruit a bit in advance, and consider cutting back on your frequency of watering if you think that might be contributing to over-vigorous growth and weak limbs.

I hope this helps,


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Tuesday, July 15, 2008

Stop-Action Quince: Part 9

Quince, Week 12 © Tyler Storey

Our quince is still alive and kicking, if admittedly somewhat lacking in high-energy dash and adventure. Such is the quiet nature of gardening.

It's the last we'll see of it for a couple of weeks, because as of today I'm taking a short vacation.

One of the great challenges in growing fruits and vegetables in the Desert Garden is that there often comes a time — usually just about now — when the desert gardener finds a need to escape the heat for a short venture to cooler climes. Vacation, in other words. Unfortunately, this tends to coincide with our mid-summer harvest and with our greatest mid-summer heat. And since nothing is more disappointing than returning from vacation to find a dead garden full of rotted produce, we need to take some steps to keep things going while we're gone.

I recommend equal parts mulch and neighborliness.

First, be certain that all your fruit trees and vegetable beds are well-mulched, and give everything a thorough soaking just before you leave.

Next, call or drop in on one or more of your neighbors. Here's the script: "I'm going to be gone for a few days, but I have lots of [tomatoes, peppers, eggplant, chiles, squash, etc.] ripening in the garden. Please come over and pick as much as you'd like."

This being Summer in Arizona, your neighbor is almost guaranteed to respond by asking if you need anything watered, to which you reply: "Thank you, if you see anything wilting that would really be great."

Don't limit yourself to the neighbors you're on friendly terms with.

This is an excellent opportunity to mend fences with those neighbors you've been feuding with all this time. Just grit your teeth, gird up your loins, march right over there and be neighborly.

Giving away food is a great way to make friends. And being neighborly is good for you.

Just remember: if you come home and everything is dried to a crisp, you can't get mad at the neighbor. That really would defeat the whole purpose.


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Monday, July 14, 2008

Back at the Ranch: Pepper Harvest

Chiles Serrano and Bell Peppers © Tyler Storey

Peppers and chiles are gratifyingly tough plants in the Desert Garden. For weeks after the tomato plants are protesting the heat and the intense Summer sun, pepper plants — given adequate irrigation — continue to put out and maintain fresh green growth. The fruits themselves may need a little more care.

One of the questions I hear with great frequency this time of year is: "Why do my peppers (or chiles) have light tan patches on them? What can I spray on them?"

No spraying necessary.

Those light tan patches, usually sunken, and sometimes slightly soft, are sun-scald. They form in areas where the fruit is subject to intense mid-day sun. If you look carefully, you'll find that they appear almost exclusively on the top or West side of an individual fruit, and in a place where there's a break in the foliage cover.

If you catch the fruit early, you can go ahead and eat it; just cut out the tan area. If you wait too long, you'll find that rot will set in and render the fruit inedible, but keep in mind that the rot is secondary to the scald and not the cause.

To prevent sun scald, keep your pepper and chile plants well-irrigated so they continue to form leafy canopy growth to shade the fruit. If you see scald anyway, construct a light frame over the plants and drape it with light shade cloth to block the most intense sun from overhead and the West. Be certain the frame is well-anchored in the soil and the cloth is well-attached; sudden monsoon winds can — and will — send your frame and cloth flying.


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When Bad Things Happen to Good Trees: Part 1

Even in the Desert Garden, there are times when we could say that no water is better than wrong water.

Last week I was called out to look at a leaning Palo Verde tree. This tree is planted near a drive, on the North side of the house, in an area altogether about 12 by 12 feet; not ideal, but not bad. The tree had been growing well, even vigorously, and was nearing 20 feet in height. Then suddenly it took a dive at about a 20° angle towards the East, partly blocking the walk into the house.

As I looked at the tree, three things were immediately apparent: first, the soil on the West (opposite the lean) was clearly broken upwards, but only for about 12 inches from the trunk. Second, there was a single drip irrigation head right where the roots were pushing up from below, again about 12 inches from the trunk; there were no other emitters in the immediate area of the tree. Third, the soil was visibly saturated on the West and bone dry on the East.

How often was the irrigation system run? Every day for twenty minutes.

A couple of things about trees to keep in mind:

  1. Tree roots have three functions: roots convey water and nutrients from the soil; roots provide storage of sugars and starches; roots stabilize and anchor the tree in the soil.
  2. Tree roots do not "seek out" water. Roots do not have eyes, ears, noses, or any other sensory organ with which to find water at a distance. Roots do, however, proliferate in the presence of water, and only in the presence of water.

The diagnosis was clear: the tree was receiving frequent shallow water in a single small space on the West side of the trunk, and this had resulted in a small root mass; the root mass was probably no larger than 2 feet by 2 feet, probably only 18 inches deep, and predominantly on one side of the tree. The area above that root mass was continually moist and loose. Once the tree reached a certain size and caught the wind just right, over it went.

Palo Verdes are very drought-resistant trees; in this instance, it would have grown more sturdily — albeit more slowly — with no water at all.

The remedy was less straightforward. Once a tree begins to fall, it's difficult to get it back upright, and rarely is this a complete success in the long term. The hard-nosed, unsentimental, and practical response is to remove the failed tree, install a new tree, and re-work the irrigation to avoid a repeat of the same problem. In this instance, we did some judicious pruning to clear the entryway walk and to lessen the canopy weight in the direction of the fall. Next, rather than try to pull the tree back upright, we decided to temporarily support the trunk in its current position and immediately rework the irrigation to begin growing a much wider and deeper root system to support the tree. Any sturdy board with a bit of padding would have worked for a support, but the homeowner wanted the support to look nice, so he promised to build one and get it under the tree that day.

Postscript: A day later the support wasn't in yet, and that evening we were hit with a monsoon-season thunderstorm that dumped nearly an inch of rain in a very few hours. Down went the tree.

The morals of the story:

  • All trees should be watered deeply — to a depth of three feet and as wide as the canopy, or wider — and infrequently;
  • Things move fast in the Desert Garden, epecially when they start to go wrong;
  • Don't let the perfect (or the pretty) be the enemy of the good (with apologies to Voltaire); and
  • You simply cannot say "I told you so" to a man whose tree is laying flat on the ground; he already knows.


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Saturday, July 12, 2008

Mark Your August Calendar

On Friday, August 1st, at 1pm, I will be presenting a workshop on Tree Selection and Planting for the Desert Garden, at the Maricopa County Home and Garden Show. The show is being held at the University of Phoenix Stadium in Glendale, and admission to the workshop is free with admission to the show.

Come spend an hour learning about some of the best trees to grow in the Desert Garden, how to select them, and how to place and plant them. And, as always, bring lots of questions.

Coming up on the calendar: This October is composting month! I will be conducting composting workshops for the City of Scottsdale (October 2), the Gilbert Library (October 21), and the City of Chandler (October 25). I'll post times and locations as we get closer.


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Friday, July 11, 2008

From the Inbox: Coffee Grounds

I received the following question from a correspondent who had recently attended one of my presentations on vegetable gardening:

I have a question about using coffee grinds around my roses, gardenias, etc. We talked about it, but I don't remember if you said how OFTEN we can put coffee grinds out there. Can you help me with that?
M., in Scottsdale, Arizona

Dear M.,
For coffee grounds, I’d go ahead and put them out as often as you like; they won’t harm the plants in anything less than truly massive quantities. You might use a small garden cultivator to scratch them into the soil a bit to aid decomposition and to head off the formation of any water-resistant layer. Coffee grounds are somewhat hydrophobic and in larger quantities can form a barrier to water penetration.

If you produce more than about a cup of coffee grounds each day, you may want to a) seriously think about how much coffee you're drinking; and b) run them through the compost pile before putting them in the garden. Coffee grounds are relatively high in nitrogen (with a carbon to nitrogen ratio of about 20:1, the same as grass clippings), and in our desert conditions much of that nitrogen is lost when applied directly to the soil. Compost is a far more stable product and less likely to result in nitrogen loss. Plus, paper coffee filters can go straight into the compost pile along with the spent grounds, where they will tidily decompose. Littering your yard with undecomposed filters is likely to attract the opprobrium of neighbors.

I hope this helps,


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Wednesday, July 9, 2008

From the Inbox: Fruit Trees and Caliche

From a Correspondent:

My wife and I are fairly new to growing vegetables here in the desert. I've read nearly every book I can get my hands on and noticed a couple things that got me wondering.
1. Is foliar feeding really effective for plants? Seems to me that with the heat so much of what I spray on the plant would get evaporated before the plant has a chance to soak it up. Some of the information I've been able to dig up on the Internet suggests that the plant can get many times more nutrients from it's leaves than it can from the ground.
2. How can I tell if I have caliche without digging down the 4-5 feet recommended by some of the desert gardening books? We plan on planting some fruit trees in our yard this winter and want to give them the best chance for survival, but don't want to just dig down 5 feet unless I really need to.
Chandler, Arizona

Good morning, Tom,

These are both great questions. The answer to both is: it's all about the soil. But since they're from different perspectives, I've answered your first question in a previous post, and we'll tackle the second question here.

When I get a question from a client or a correspondent that includes "fruit tree," "caliche," and "dig down five feet," I know exactly what book they've been reading. It's a great book and very useful for learning about growing fruits and vegetables in the Desert Garden — except in this one instance, where it goes terribly astray. Don't do it!

Caliche is a hardened layer of calcium carbonate that sometimes forms a subsurface water-impermeable layer in some areas of the desert. Where it's present it can be a concern because it can interfere with drainage and can, if shallow enough, prevent tree roots from anchoring deeply in the soil.

As a side note, other soil issues can be mistaken for caliche. In newer developments, we sometime find a layer of clay soil that's been compacted by heavy construction equipment: this is called hardpan. In houses built on former agricultural lands, we sometimes find a layer of impervious compacted soil caused by years of plowing at the same level: this is called plowpan. Either can restrict root and water movement in a manner similar to caliche, but they're not the same thing.

To your question: not only do you not need to dig down five feet deep, but you really shouldn't dig down five feet. It's a very bad idea.

While I'm tempted to just answer your question and tell you what to do instead of a five-foot hole, I'm first going to explain the whys and wherefores. I can't help it.

There was a time when the recommendation for planting fruit and other trees in the Desert was to dig a hole five feet deep and five feet across, and then plant the tree in the hole, replacing a huge portion of the removed soil with organic material such as compost or rotted manure, or wood chips. The idea was that you could get through the caliche layer (if there was one) and also provide the tree with good soil in which to grow.

More recent research has demonstrated that there are two problems with this advice. First, it simply isn't possible to dig a hole large enough to provide "good" soil for the mature root growth of a tree. Consider that an apricot tree, for example, will grow a canopy 15 feet wide and have a mature root area somewhat larger than the canopy. To accommodate the mature root area, you would have to dig a hole 25 feet wide and five feet deep, in the process moving approximately 2500 cubic feet of soil. If you decide to try that, let me know: I want to come watch.

If instead you decide to improve the soil in a smaller area — let's say a five by five hole — one of two things will happen: either the tree will grow roots only into the improved area and thus have a small root area with poor anchoring and consequently be subject to poor development and wind-throw, or the tree will happily send roots out into the surrounding, unimproved, native soil, in which case it was a waste of time to improve the soil in the first place.

The second problem with improving the soil for a tree with organic amendments is that organic amendments break down. All that manure and compost and wood chip will decay and in the process get smaller. And the tree that you've planted on top of all that lovely organic matter will sink. It will sink a lot. It will become — to belabor the point — a sunken tree.

Sunken trees aren't good. Sunken trees collect water in a very small area near the trunk and consequently develop small root systems and become susceptible to rots at the base of the trunk.

A sunken tree also means that your tree is, as above, pretty much growing in native soil. Which means all your amendment was a waste.

So, here's what you do instead of digging a five-foot hole: dig a one-foot-deep hole where you want to plant your tree, about a foot or two wide. Fill the hole with water. If the water drains out completely within about a half a day, then you're all good to go. Let the soil dry a bit (never dig wet soil), then dig out the hole only as deep as the root ball of the tree you're planting, and about three times as wide. Remove the tree from its container, place it in the hole, and back-fill with only native soil, keeping the top of the root ball at ground level (no mounds and no "bowls"). Water it well and them mulch heavily and widely with an organic mulch such as fine chipped bark, keeping the bark slightly away from the trunk.

If the water doesn't drain within half a day, take a soil probe (a piece of rebar or a really long screwdriver) and push it through the bottom of the hole. As deep as it goes is how deep your obstruction is. At that point you can either dig down to try to break through the obstructing layer, or you can try the water test in another part of the yard. If you're fairly certain that the obstruction is at least three feet deep, go ahead and plant the fruit tree anyway; three feet of soil is going to be good for almost any fruit tree. In either case, dig only as deep as you must, and never back-fill the hole with anything other than native soil.

At this point you may be wondering why yesterday I told you to add lots of organic material to your garden soil, and today I'm telling you to not add any organic material to your tree soil. That's because organic material always breaks down, and so it takes multiple additions over a long period of time to make real changes to your soil. In a vegetable garden we can add more material — and new plants — several times during the year and eventually make a lasting change, while in planting a tree it's a one-shot deal. Trees eventually will grow into native soil, and they will be stronger and healthier if they just get used to it from the beginning.

That gardening book you've been reading is full of great information from a much-respected gardening expert, and you can learn a lot from it. Except those pages on caliche and the five-foot hole; just skip over those and we'll pretend it never happened.

I hope this helps,


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Tuesday, July 8, 2008

From the Inbox: Foliar Fertilizers

From a Correspondent:

My wife and I are fairly new to growing vegetables here in the desert. I've read nearly every book I can get my hands on and noticed a couple things that got me wondering.
1. Is foliar feeding really effective for plants? Seems to me that with the heat so much of what I spray on the plant would get evaporated before the plant has a chance to soak it up. Some of the information I've been able to dig up on the Internet suggests that the plant can get many times more nutrients from it's leaves than it can from the ground.
2. How can I tell if I have caliche without digging down the 4-5 feet recommended by some of the desert gardening books? We plan on planting some fruit trees in our yard this winter and want to give them the best chance for survival, but don't want to just dig down 5 feet unless I really need to.
Chandler, Arizona

Good morning, Tom,

These are both great questions. The answer to both is: it's all about the soil. But since they're from different perspectives, I'll answer your first question here, and the second in a following post.

Foliar application of fertilizers pops up every now and then as "the" answer to gardening, sold primarily on being fast. Fast, however, isn't really our goal in home vegetable gardening. If we were really looking for fast, we'd just pop down to the grocery store and load up the cart with produce. That's much faster.

More to your point: I would suspect, though I have seen no studies to back it up, that evaporation would tend to limit the availability of the fertilizer to the plant. And — because all fertilizers are salts — that leaves us with a residue of salts on our plants' leaves, which seems unwise.

On a — literally — deeper level, though, there are greater problems with foliar feeding. First is the name: even though we talk about "feeding"our plants, and foliar "feeding," the truth is we don't feed plants. Plants create 100% of their own food through the process of photosynthesis. Real plant food, despite advertising to the contrary, is made up of sugars and starches created within the cells of the plants. The elements of fertilizer — nitrogen, phosphorus, potassium, iron, sulfur, magnesium, etc. — are simply among the elements that plants use in the creation of their food. They are not food itself.

Which brings us to your next point: while it is possible that plants may be able to absorb many times more nutrients through their leaves than from the ground, I have my doubts about this, having seen studies on both sides. But what we do know to be fact is that plants can absorb from the soil all the nutrients they need. And excess beyond need, is, well, excess.

So, to cut to the chase: gardening, especially vegetable gardening, is all about good soil. And foliar feeding does nothing to develop good soil. Save the money that you might have spent on foliar fertilizer and invest in organic soil amendments instead. Compost is excellent, as is rotted cow manure. Organic soil amendments will add nutrients to the soil, improve water retention and drainage, increase the levels of biotic activity in the soil, probably decrease pH levels — which will increase nutrient availability — and in general be beneficial to your plants.

Spraying foliar fertilizer may give a plant a one-time boost, but incorporating organic materials into your soil at the beginning of every planting season will consistently and continually improve your soil over time. And it's really that improved soil that will give you a good crop of vegetables. If in the future you suspect that you have a deficiency of a particular element — nitrogen, for instance — then side-dress your plants with an organic fertilizer applied to and worked into the surrounding soil. It may take longer to benefit the plant, but it will also have a longer-term benefit to the soil. And that's really the whole secret to growing vegetables in the Desert Garden.

I hope this helps,


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Monday, July 7, 2008

Building Blocks: Summer Harvest

The best part of growing your own fruits and vegetables is, of course, in the harvesting and eating. But when it comes to harvesting the fruits and vegetables that ripen in the Summer heat, a little extra caution is in order.

Conventional gardening wisdom tells us to harvest early in the day, when temperatures are cooler and plants are full of moisture. But right now, when daytime temperatures in the Desert Garden are consistently above 100° and night temperatures are not much lower, "cooler" hasn't much practical value.

For the most part, our fruits and vegetables do just fine in the extreme heat as long as they're attached to, and receiving moisture from, the plant. It's interesting, really: that pepper out in your garden, for instance, may itself have a "body" temperature of 85°, but it's fine. If we think about it though, we realize that the moment we sever that pepper from its stem, it becomes a piece of fruit sitting around at 85°. And if you've ever left fruit sitting out on a warm kitchen counter or, even worse, in the back seat of the car, you know that warm produce deteriorates very quickly.

We can lose a lot of our harvest in that fast transition from growing fruit to harvested produce; what we call "field heat" starts to degrade fruits and vegetables almost instantaneously. I once lost a dozen apples through just leaving them in the basket, figuring they could handle the couple of hours until they became pie; every one of them turned brown on one side in the interval and were unusable.

There are two easy methods for dissipating field heat, and cooling your produce. The first is to simply place the produce in a sink full of cold water until it's cool, and then drain. The second method is to lay the produce in a single layer on a refrigerator shelf; use a single layer with no container so the heat dissipates more quickly. Fill the sink or clear a refrigerator shelf before you head out to the garden to harvest in any quantity, so you can pop the stuff right in. Our tap water is often warm this time of year, so you may need to add a few ice cubes to cool it down, but don't make it freezing. Leave the produce long enough so it's cool all the way through, and then store or use it.

There's an even better harvesting method for use with tomatoes: stand in middle of tomato patch; pick tomato; eat tomato right there and then. Repeat as needed.


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Thursday, July 3, 2008

From the Inbox: Leafcutter Bee Nest Update

Bamboo Bee Nest © 2008

Back in May of this year, I had a number of inquiries about Leafcutter Bees, and posted a note about Leafcutter Bee nests from bee expert Stephen Buchmann (click here to read his response). Corinne, in Paradise Valley, Arizona, kindly sent along this terrific photo to show her new bee nest in action (click the photo to enlarge). Note that it's essentially a collection of bamboo tubes bundled together. The bee has been lining each tube with leaf pieces to create cells, laying an egg and a food supply in each cell, and then capping off the ends with more leaf. A very simple and effective way to host these great pollinators in your yard.


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Wednesday, July 2, 2008

Desert-Adapted Trees

A recent correspondent who wrote to ask about planting "special" trees, has sent along a follow-up question about what kinds of low-water trees to plant. Perfect timing: Summer is the time to learn and plan, and Autumn is the time to plant.

Over the next few days, I'll introduce you to a number of very good desert-adapted trees. To start, take a look at the Desert Ironwood here.


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Tuesday, July 1, 2008

Stop-Action Quince, Part 7

Quince, Week 10 © Tyler Storey

As today is July 1, we can be hopeful that our intrepid quince has survived June Drop; technically, it could still happen, but why dwell on unpleasant possibilities?

In the cooler and wetter Spring pollination season, fruit trees tend to pollinate and set a large number of fruits. As the year progresses and we enter the drier and considerably warmer early Summer months, the trees end up burdened with more fruit than they can handle and they start shedding — dropping — the excess. We walk outside one morning and find the ground littered with half-developed fruit. I know to expect it, but I still find it alarming.

Living plants create energy in the form of sugars and carbohydrates through the process of photosynthesis. Of the many ways we can consider the parts of any plant, one way is to consider the various parts as being in one of two categories: those parts that create energy, and those parts that use energy. Fruits definitely fall into the latter category; fruits are energy sinks, and draw a huge portion of energy from a plant. If a fruit tree has more energy users — fruits — than it can support with its energy producers — leaves and such — then it begins shedding the unsupportable extras; some are sacrificed so that the available energy can go to the survivors.

It's a little bit like when you're running the toaster and the coffee pot and the waffle iron and the stand mixer and the light above the sink all at the same time and the circuit blows. Not quite the same, of course: we don't have to sacrifice the waffle iron for the greater good of the toaster; we just re-set the circuit breaker.

When you see June Drop, don't panic; do be certain that the tree has adequate but not excessive water; and throw the falls on your compost pile, where they will still be of some utility.


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