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, April 30, 2008

From the Inbox: Spider Mites on Italian Cypress

From a Correspondent:

I live in Gilbert, and am looking for some help in saving my Italian Cypress. I planted 4 Italian Cypress in May 2007 each 5 gallon size. They have been doing very well (now almost 8+ gallon size) until a few days back. Out of four, I am seeing a problem in two of them. They look whitish or pale, dusty from the bottom, and have spider webs. I suspect spider mites, but am not sure. They get water regularly. I am wondering what is going on. Thank you for your time.
Rajesh, Gilbert, Ariz.

Rajesh, good afternoon,
From the picture you attached (below) I would say your diagnosis is spot-on: you have spider mites on your Italian Cypress.

Spider Mites on CypressMites aren't true insects, but rather arachnids. Mite infestations are increased by cultural conditions; hot, dry, and dusty conditions greatly favor their development. Importantly, broad-spectrum spraying of insecticides in the landscape tends to increase mite populations and their damage, sometimes explosively, because it eliminates their natural enemies. Some insecticides have even been found to stimulate mite reproduction directly.

There are two things you can do to try to control your existing mites, both fairly easy because your plants are still small.

First, once a week, in the morning, hit the plants, especially the infested area, with a strong blast of water from the hose – strong enough to really blast the little critters but not strong enough to damage the trees.

If that seems ineffective, use an insecticidal soap to spray the plants, being thorough and following the directions on the label exactly. There are miticides that are available, but those tend to be strong chemicals, and are probably not necessary.

I have had great luck with the water-blast method.

To help prevent severe mite infestations in the future, wash off your plants occasionally during the hot and dusty times of the year, and limit or eliminate pesticide spraying in and around the landscape.

I hope this helps,


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From the Inbox: Clay Soil

From a Correspondent:

What needs to be done to amend very dense clay-type soil? I have a small backyard with no plant life and would like to add suitable landscape plants to this full-sun environment.
A., in Mesa, Ariz.

Good morning A.,
A very dense clay soil can seem a bit daunting in planning your landscape, but the good news is that our desert plant varieties will thrive in it once they get in it and get growing. Consider yourself lucky: clay soils have excellent water and nutrient holding capacities and are much easier in the long run than are sand or sand/rock soils.

First, let me encourage you to not try replacing the soil with "custom-made" stuff. There are a number of reasons, including expense and impracticability, but mostly because it won't work. You'll never be able to"replace" it deeper than a foot and keep in mind that even the humblest wildflower has roots a foot deep, while shrubs and trees have roots that go, respectively, 2 and 3 feet deep, or more.

When we replace soils, lay a layer of soil on top of existing soil, or very heavily amend our soil, we create what's called a "soil interface," a zone that roots and water have difficulty crossing. If you replace your soil, one of two things will happen: either the roots and water will not cross the interface and you end up with shallow-rooted and drought-vulnerable plants, or the roots and water do cross the interface and happily grow in the native soil — which means it was waste of time to put the new soil there in the first place.

The biggest challenge with dense clay soils is opening up the surface to initially improve the water infiltration. Once you do that and then get your plants growing, the plants will take care of the rest. I would recommend you try this: water your soil slowly to a depth of about 1 foot — slowly so the water has time to penetrate without running off. Then wait a couple of days until the soil has dried enough to be diggable but not wet (never dig wet clay). Look for a crumbly texture when you put your spading fork in it.

Next, spread a 3-inch layer of organic mulch on the surface, preferably quarter-inch bark chips or wood chips 1/2 inch or smaller. You can get the bark chips bagged at home stores, or wood chips free from some power companies or arborists. You want something small, but with some substance to it.

Either with a spading fork if you're feeling muscular, or a tiller if you're not, work those chips well into the first few inches of the soil. You can add more and work them in deeper if you want. What those chips are going to do is open the top layer of your soil for water infiltration.

Next, start planting your desert-adapted plants, and be sure to plant them without adding organic material to the back fill. Dig your holes 2-3 times as wide as the plant's root-ball but no deeper. And, again, back-fill the holes with only the soil you took out of the hole.

After you've planted, top-mulch your soil 3 inches deep with an organic mulch: more of the bark or wood, or something else organic. Don't use gravel on this soil. Over time, your top organic mulch will slowly break down and help to keep your soil open. Add a little more each year as needed.

Do be careful to not walk on your newly fluffy clay soil when it's wet, as that will re-compress it. And, lastly, water your new plants deeply, slowly, and infrequently: 1 foot deep for ground covers and wildflowers, 2 feet down for shrubs, and 3 feet down for trees.

I think you'll find this will help you and your plants get the most out of your clay soil, and with minimal effort and expense.

I hope this helps,


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Tuesday, April 29, 2008

Just a Thought: Insects

Insects, in and of themselves, are not bad or even, for that matter, necessarily good. Cockroaches, caterpillars, bees, moths, termites, ants, butterflies, and all the rest of them, are simply creatures going about their appointed business. It is only within the context of our interaction with them where we can begin to legitimately label them with a value: good or bad. Even then, it is to the interaction that the label properly belongs, not to the insect itself.

Termites eating your house are, as far as you're concerned, bad. That seems fair. Termites eating organic matter on the forest floor, through which action they enrich the soil, provide nutrients for plant growth, and keep us from being up to our necks in dead trees, are indisputably good.

The bees that pollinate our fruits and vegetables are, by human standards, among the most important, valuable, and good insects on Earth. The bee that stings you on that sensitive fleshy part of your inner arm you might be excused for calling indescribably bad, perhaps with a few choice epithets thrown in for emphasis.

An Orange Dog caterpillar on your brand-spanking-new five-gallon citrus tree may well wreck it, while the same caterpillar on your established lemon tree is unlikely to cause any damage and is a fascinating example of mimicry. It will soon turn into a beautiful butterfly, the Giant Swallowtail.


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Monday, April 28, 2008

From the Inbox: Leafcutter Bees

From a Correspondent:

I have a rose bush whose leaves are being eaten. A neighbor told me that the culprit is called a leafcutter bee. How do I kill them so they don't kill my rose?
R., in Phoenix, Ariz.

Dear R.,

There is nothing practical you can do to kill the leafcutter bees, but you don't need to worry about them killing your rose bush: they won't kill it. That's good news for both you and the bees, because leafcutter bees are an important natural pollinator, and we really don't want to kill them.

Pesticides generally work either by contact — they get on the target insect — or through ingestion: the target insect eats the pesticide directly or incidentally. Ant and cockroach baits are examples of direct ingestion, and systemic and topical poisons that are eaten when an insect sucks the sap or eats a part of a plant are examples of incidental ingestion.

The reason we can't kill the bees through ingested poison is because they're not actually eating the leaves; they're cutting out segments of the leaves to use for building their nests. We can't kill them through a contact pesticide because they're bees and they fly faster than we can spray them. While you could in theory stand in your yard with pesticide and spray everything that moves, I doubt you would have much luck, and your yard would be toxic as a result. Keep in mind that almost anything that can kill an insect is bad for you, too.

Leafcutter bee damage on grape © Tyler StoreyWhile leafcutter bees do cut holes in the edges of leaves (see picture), they rarely, if ever, do enough damage to compromise the health of the plant. Unlike grasshoppers and caterpillars, bees tend to take a small bit from a number of different leaves rather than destroy entire leaves en masse. The damage can be unsightly, but weighed against the bees' role in fruit and vegetable pollination, it's pretty minor.

And since there's really nothing we can do about them anyway, it's just as well to accept them as one of the quirky, interesting parts of living in the Desert Garden.

I hope this helps,


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Saturday, April 26, 2008

Back at the Ranch: Artichoke

artichoke bud © Tyler Storey The third artichoke of the season. Numbers one and two were but the remembrance of lunch past before I thought to take a picture of them.

Artichokes (Cynara scolymus) thrive in the Desert Garden with minimal care. The plants are large, forming a silver-green fountain perhaps three by three feet, so do give them plenty of room, but they're also a highly decorative addition to the landscape, so no need to tuck them back into an inobtrusive corner. You may need to experiment with the best location for artichokes in your garden; I've found they do well with some light dappled or afternoon shade.

Because they're a perennial vegetable, living and producing year after year, plant them in an area of well-prepared soil where they can remain undisturbed by annual gardening activities; try planting plants in early Autumn to give them a head start. Water them well during their growth season, about once a week; less if the soil stays moist longer. Mulch them well and you'll find they need surprisingly little irrigation; they're a member of the thistle family, and thistles are tough.

Harvest the buds when the scales are still tight, cutting with a sharp knife about an inch below the bud base. Steamed and served with melted butter is a classic presentation. If you have Summer Savory growing in your herb bed, throw a few sprigs into the melting butter; it has a fresh tart flavor that perfectly complements home-grown artichokes.


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Composting: Moisture

As the weather in the Desert Garden gets steadily warmer, now is the time to develop the habit of keeping your compost pile consistently moist. A compost pile has four necessary ingredients: carbon, nitrogen, water and air; whenever any one of the four is missing, the process grinds to a halt. Our standard is to keep the pile as moist as a wrung-out sponge.

You don't necessarily have to rely on hose-water alone. Leftover coffee goes into the pile (black, with sugar or without, no cream), as does unsalted cooking water from the kitchen, flat soda, leftover fruit juices, and similar liquids. If your hose is warm from the sun, empty the first flush of hot water onto the compost pile before you water your plants.

If your pile does dry out, you will end up with petrified plant material instead of compost. You can get it started again by adding more "greens" — nitrogen-rich plant matter — and water, then turning it well. But it will take less water in the long run if you keep it moist from the start.


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Friday, April 25, 2008

Back at the Ranch: Hollyhock

volunteer hollyhock © Tyler StoreyThe first hollyhock blossom of the season. I planted hollyhocks in this yard only once, eight or nine years ago, and they have ever since been happily re-seeding themselves wherever they find a comfortable place to grow.

Allow at least a few of the blossoms to set and mature seed, then toss the seed randomly about your yard, or leave the plant to manage on its own. Pull out those plants that come up in inconvenient places, and let the rest grow as they will.

While some modern hollyhock hybrids will grow and flower in a single year, as they re-seed over several generations, they tend to revert to their natural biennial cycle, sprouting and growing one year, then blooming the following year. They also tend to revert to a purple-rose color, as in the picture. It's a lovely color, but if you want to keep other colors coming up, simply cut off the flower stalks of your least-preferred colors before they set seed. Each Spring will surprise you with a new batch of unexpected petal shapes and colors.


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Thursday, April 24, 2008

Building Blocks: Botanical Names

You don't need to know the botanical names of plants to be quite successful with gardening. Many a gardener has happily gardened for decades on end, never knowing the difference between a Fouquieria and a Fragaria, and yet never mistaking an ocotillo for a strawberry. But there does often come a time in a gardener's life when botanical names become not only interesting, but useful, and it is in preparation for that possible moment in your life that I offer the following primer on botanical names.

First, if you hear the phrases "binomial nomenclature" or "binary nomenclature," don't let them throw you for a loop. Those are simply terms that mean "named with two names." Most people you come across, with the notable exception of certain members of the music and recording industry, are also named with two names. And that's the first thing to keep in mind: Plant names are pretty much like people names.

Like many people names, plant names tell you the name of the general group to which the plant belongs, and the specific name of that particular plant. So, if I were a plant, my general group name would be my family name — Storey — and my specific name, to distinguish me from all the other members of the Storey family, would be my first name: Tyler. Instead of Tyler Storey, my plant name would be Storey Tyler. And that's the second thing to keep in mind: Plant names are like people names, but their "family" names always go first. In many parts of the world, that's also true for people, but let's not confuse things.

We call the general group to which a plant belongs its "genus." And that's easy to remember, because "general" and "genus" derive from the same word and mean about the same thing. We call the specific name of an individual plant the "species." And that's also easy to remember because "specific" and "species" also mean about the same thing. It couldn't be simpler: Genus means general, and species means specific. So, for instance, a Palo Brea tree is in general a Parkinsonia, and specifically a praecox; taken together, its full name is Parkinsonia praecox.

So now you know: every plant has a botanical name of two parts, its genus and its species, as for instance, Fouquieria splendens (ocotillo) and Fragaria chiloensis (strawberry). And if you're thinking that those two names are going to be impossible to memorize, then here's the next thing to keep in mind: Plant names are like people names, and we learn them as we get to know them and spend more time with them. There's no rush and, unlike with people, there's rarely that awkward moment when we meet them in the grocery and can't remember what to call them.

Now, if you've spent any time at all looking at plants for the Desert Garden, you probably already know plants such as eucalyptus, acacia, oleander, ruellia, lantana, bougainvillea, agave, yucca, and penstemon. Those are all botanical names, which means: You know a lot of botanical names already.

One way to learn plants' names is to learn something about the plants themselves. Fragaria, the name of the strawberry genus, derives from the Latin word meaning "sweet-smelling," which of course stawberries are. And the species name of the domesticated strawberry, chiloensis, means "from Chile." So remember, if the names seems confusing: Plant names always have meanings.

And finally — because this is only a primer and I'm keeping it short — don't ever worry about how to pronounce a botanical name. Plants do not have ears and will never mind if you pronounce their name incorrectly. And why should anyone else care?


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Plant to Ponder: Red-Flowered Prickly Pear

Opuntia aciculata, also called Red-Flowered Prickly Pear and Chenille Prickly Pear, is one of my favorite cacti for the Desert Garden. While many prickly pears have wonderful yellow flowers, this one stands out by bringing forth bright scarlet blossoms at a time of year when there isn't a whole lot of red in the low-water landscape. It eventually grows to about 3 feet tall, usually a bit less, and several feet wide; takes full sun, or the very lightest of filtered shade; and requires little or no water once established.

Opuntia aciculata © Tyler StoreyIts species name, aciculata, derives from the Latin for "needle-like," and the common name "Chenille" refers to the same characteristic: prominent clusters of sharp glochids that dot its surface in an evenly spaced pattern, much like a chenille bedspread. Don't let these scare you away from this plant. All Opuntia have glochids, and the fact that these are large and prominent on O. aciculata not only makes this a wonderful-looking plant, but also makes it a safer plant: you can see them to avoid them, and they are large enough to easily remove if you do get stickered. It's the ones that stand around looking innocent that you have to watch out for.

Use O. aciculata as a low specimen plant, as a medium-textured foreground plant for fine-textured desert trees, for red color following wildflower season, and anywhere you'd like to have a prickly pear that's just a bit different from the everyday varieties.


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Wednesday, April 23, 2008

Coming Soon to a Grape Near You

Adult Skeletonizer Moth © Tyler Storey The Western Grape Skeletonizer is one of the most irritating pests of the home grape grower, and one of the most interesting. This blue-black moth, about half-an-inch long, lays her yellow eggs in clusters on grape leaves in early May. After they hatch, the yellow, black, and blue striped larvae line up in a tidy rank on the leaf and march across it, eating the leaf tissue as they go and leaving behind a "skeletonized" leaf. It's like synchronized eating. Once they finish their communal feed, each caterpillar heads off to find its own meal on a nearby leaf; with sometimes dozens of caterpillars hatching on a single leaf, they can strip a large grape vine in very short order, so the key is to stop them while they're still in a group.

There are four steps to controlling the Grape Skeletonizer:

  1. Very soon you'll see the blue-black adult moths fluttering around your grape vines. You may even see the male moth doing an intricate little courtship dance on a grape leaf, hoping to impress nearby females. Nip this romance in the bud by swatting any adult that you see.

  2. After the romance has ended, look around your grapevine for small yellow eggs laid in clusters on the undersides of your grape leaves. When you see them, squash them.

  3. As the month progresses, stand back and cast a keen eye on your grape vine. What you're looking for is small silvery patches on the leaves; that's the first sign that the caterpillars have hatched and are beginning their march across the leaf. Get up close, and check the undersides. When you find a leaf with caterpillars on it, cut the leaf off the plant and destroy it and its residents. Keep looking; you missed a few.

  4. Once the caterpillars have each moved to their own leaf, you'll see damage across the vine, and it happens fast. At this stage, your best tool is to spray BT (Bacillus thuringiensis) on the vine, following the directions and being thorough. BT is completely organic and safe to use on edibles. The caterpillars will ingest the BT spores with the leaf matter and come down with a terminal stomachache.
As with any plant that we grow to eat, there's no point in spraying toxic chemicals, and really no need to. It does take a little vigilance, but once you understand the life-cycle of the insect and gain the habit of what needs done, it will become simply another part of your daily stroll through the garden.


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Mark Your Calendar

I will be presenting two landscaping seminars this coming Friday, April 25th, at the Maricopa County Home and Landscape Show.
Come by the Garden Pavilion at the Arizona State Fairgrounds at 2:15 to learn all about selecting and planting trees, then stick around for a seminar on managing heat, dust, waste, and water at 3:00 pm.
We'll cover everything from what kind of tree to buy, to where and how to plant it, followed by an overview on how your landscape can save you money, water, and air-conditioning costs. Attendance is free with admission to the Home and Landscape Show.

See you there,

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Tuesday, April 22, 2008

From the Inbox: Cactus Offsets

From a Correspondent:

We have four golden barrel cacti in our yard. Two of them have started growing mini cacti on them. One of them has at least 30-40 growing on it. This cactus suddenly turned rotten on the crown. Three questions: 1. Are the mini cactus growing on the main plant normal? 2. If they're normal, any idea why the crown rotted? My wife thinks the excessive growths "sucked" the life out of the cactus. We only water the cacti once or twice a month. 3. What do we do?
C., in Gilbert, Ariz.

Dear C.,
Congratulations: you are witnessing one of the coolest events of the desert garden. Golden barrels (Echinocactus grusonii), are normally solitary, but when the terminal bud (the growing point in the center) is damaged, the plant responds by producing the offsets that you're now seeing. It's a reproductive strategy to ensure the survival of the plant.

Not to worry: the main cactus didn't get killed by the offsets; the offsets formed because of damage to the main cactus. It's hard to say of course, what might have caused the damage. It really doesn't take too much. I know of nursery professionals who initiate offset growth by bouncing the eraser end of a pencil on the growing point. Depending where on the main cactus the offsets are growing, they may well continue to grow even after the main stem has rotted out beneath them. If it appears that they are wholly surrounded by rotting tissue, you may want to try twisting off a few of them and seeing if you can root them independently. But, in the spirit of discovery, if I were you I would let it go and see what happens.

As to the water, it partly depends on your drainage and their sun exposure. Golden Barrel in well-drained soil in full sun will need good water, but if your soil is at all clay or if they are in shade or part shade, you might try backing off the water just a bit, and see how they do then. If your other two Golden Barrel are doing well, though, chances are your watering schedule is fine. Just be sure you don't water so much that you rot the roots, or so little that the plant shrivels and turns yellow.

Remember, for all desert plants, water should be deep, but infrequent.

I hope this helps,


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From the Inbox: Grasshopper Attitudes

From a Correspondent:
I am just beginning a vegetable garden in a newly enclosed 7 ft. tall chain link fence (30' x 30'). It is protected on the ground near the outside of the fence and a foot above the fence with chicken wire, and underneath the gate is a strip of cement. I will later put on bird netting. You would think this would protect the garden from animal predators. But I forgot about the grasshoppers!!!!

The garden is in a remote area about 12 miles southeast of Tombstone, in Sunset Western Gardening Zone 10, and it is near a sacaton meadow that during the summer is filled with grasshoppers 3 or more inches long. The fence will not stop the grasshoppers, will it? Will my garden be decimated as after a horde of locusts descend? Is there anything I can do to protect against these insects?

I also plan to plant artichokes outside the fence along the sacaton meadow. Will grasshoppers get the artichokes, too?

J., near Tombstone, Ariz.

Dear J.,
Grasshoppers are notoriously difficult to control. By dint of form and habit, they are nearly unassailable, so don't bother with chemicals of any sort. Anything you spray or sprinkle will at best annoy the grasshoppers and defeat the healthy reasons for growing vegetables at home, and at worst render your garden toxic. Exclusion also won't work, and anything that did work would exclude your pollinators as well. Birds are among the few natural predators of 'hoppers, so you don't want to permanently net them out of your garden.

Grasshoppers will, if pressed, eat nearly anything green, so the artichokes are in play as well.

Your primary defense against grasshoppers is a proper attitude. There are several that might prove effective, singly or in combination:
1) Humility: Grasshoppers are the things that remind the gardener that no matter how much we think we're in control of our gardens, Nature still has the upper hand.
2) Camaraderie: An infestation of grasshoppers will prevent your exclusion from those friendship-building conversations with other gardeners which are predicated on gardening woes.
3) Vigilance: The possibility of grasshoppers will avert your being lulled into gardening complacency by your wire, concrete, and netting.
4) Pride: You will appreciate the vegetables that made it through the danger ever so much more than any that simply plodded through unchallenged; the Prodigal Vegetable, if you will.

As a secondary defense, I highly recommend the scissors method, which I use with some good effect in my own garden. This involves keeping a good pair of scissors by your side and using them to snip the offending critters in two. Barbaric, yes, but highly effective with only a little practice, and an excellent method for keeping up your eye/hand coordination. It works best in the cool of the morning, when your intended targets are still sluggish. Once you develop an eye for spotting chewed leaves and then tracing back along the stems to find the culprit, you'll find it's a snap.

And lastly, on the off chance that you might consider raising chickens, you can let your hens loose in the garden enclosure to do some of the snipping for you, provided that you keep them away from tender seedlings. Chickens are pros at grasshopper nabbing. This has the added advantage of providing a steady supply of high-protein fresh eggs to go along with all your fresh produce. For added amusement, don't tell your breakfast guests what the hens have been eating until after they bite into their eggs.

I hope this helps,


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