Desert Heat

115 Degrees Fahrenheit. In the shade. On the East side of the house. At 5:00 PM CST

One could say that is is just a little warm today here in the Mojave Desert on June 21st.  This is day three of temperatures over 112 for us here in Sunset Zone 9a in Fabulous Las Vegas.  We are on the East side of town but low enough at the base of the foothills that it's not the coolest part of town. That would be up on the slopes of Mount Charleston, where it seldom exceeds 95.  But there are warmer spots such as down in Laughlin, NV where it got up to 120 yesterday. 

So, what does a gardener do when it's this hot? Try to keep perennials as comfortable as you can.  That means three things: mulch, shade and water.  Mulch we've already taken care of as mentioned in previous posts.  We've supplemented it a bit with the stems of 'bonus plants' which have either ended their annual life cycle already and/or succumbed to the heat. 

Dead 'bonus plants', dormant Bermuda grass (also bonus) and wood chips insulate the soil here.

 

 

 

 

 

 

In the case of this West facing car port, all we can do really is try to insulate the creeping acacia with mulch and try to keep a few standing 'bonus plants'. 

Tree and shrub branches under cloths keep these shelves shady.

We've also amped up the shade with trimmed limbs and cloth on the shelves along the East wall. As well as moving more shelves over there to help get more of the plants into afternoon shade.  The big elm tree helps (and the tree itself is doing well thanks to the soaker hoses) shade the plants for part of the afternoon, but unfortunately, the setting sun gets under it in late afternoon. 


Our new catclaw acacia will someday be able to handle the heat fine on its own, but it's still a little sapling, so we are trying to help it out with extra afternoon shade......

This old lawn chair is just right for PM shade for our little catclaw acacia.

......courtesy of an old lawn chair that I keep around even though I probably should get rid of it.  I'm glad I kept it this year as it's fairly tightly woven mesh back is just right to give this little catclaw acacia some afternoon shade when the heat is the worst. 

Then, there is water.  It's tricky to deal with in this heat as you don't want to over-water anything and drown the roots. On the other hand, plants evapotranspirate (a combination of purely physics based evaporation along with plant energy requiring transport of water from roots to the rest of the plant)  and use water to cool themselves more than what they actually use to grow. This is especially the case when it is so hot outside. It's one thing for a plant to keep its cells cool while they grow, respire and (in some cases) carry out photosynthesis - all of which produce heat in the plant.  It's quite another when the air outside the plant is even warmer than the plant's normal temperature. 

When that happens, most plants will take up more water than usual as long as it isn't too hot.  When it gets above 80, most plant processes begin to slow down and growth usually stops.  Almost all plant processes stop when it gets well above 100.  Then the plant enters a sort of dormancy state but it is not as dormant as some plants get when it is too cold in the winter and still needs water and other nutrients.  Then, when it cools off at night (even as hot as its been here, it gets down to the high 70's - low 80's at night this time of year), the plant will resume growth and most other processes.  I've observed the most growth on closely monitored plants in the morning after a cool (or at least somewhat cooler) night.  

Even 'drought tolerant' and desert native plants behave this way to a greater or lesser degree. It's part of what makes them able to live in such hot places as they are better at shutting down and insulating their stems and leaves from outside heat than plants from wetter, cooler places are.  So, we increase our watering times from the once a day schedule in late Spring (the weather, never what the calendar says) to two times a day (early morning and early evening - never water in the middle of the night as that's a ticket to fungal problems) in June to ever six hours or so during the day when it is above 110. 

We can do this without over-watering the plants because we are using soaker hoses which put out about 1/4 a gallon of water a minute for every 10 feet of hose under the typical house's hose bib delivery capacity of 30 gallons per minute.  And we run the hoses for 30 minutes each time. That comes to a total of 3 gallons per foot of hose covered area each day.  This is enough, when you estimate losses from evaporation, to get about an inch of water in the top 2 inches of the soil (if the soil drains well) and hopefully, part of an inch soaked down deeper into the soil to encourage a deeper, better root system.  Evaporation is not a total loss though, because it helps cool the soil, plants and the air immediately around the plants. Yes, it is good to try to minimize evaporation, which is part of what mulch and shade do, but some evaporation is necessary, especially when it is this hot.

This clay pot without a drain makes a great evaporation basin.

That's why I encourage evaporation pans like these around plants in dry climates. It helps simulate an environment that you'd have near a stream or pool here in the desert where the more showy plants that we like to have live in nature.  This clay pot in the above picture doesn't have a drain hole. I found it at a thrift store and figured it was a perfect little mini-water storage basin.  Placed under the soaker hose, it catches some of the water and stores it, releasing it by evaporation slowly thanks to how small diameter it is relative to how deep it is.  Plants nearby enjoy a somewhat more humid, cooler microclimate like what they'd have at the edge of a pond. 

This volunteer sunflower wilts each afternoon.

   For some plants, all of this effort isn't quite enough, but some are hanging in there and kinda bouncing back by morning like this volunteer sunflower.  This sunflower is getting some water from a soaker hose, so it does well in the morning and early afternoon, but is rather wilty by evening.  If it survives to bloom, great. If not, I won't be terribly surprised. 

These wildflowers are doing just fine.

Other, more desert adapted or native plants are doing much better like these wildflowers from a mix that I broadcast last fall.  In fact, they didn't bloom until a couple of days ago. 


We'll see how everything turns out once things start cooling down again.  I wish you luck with keeping your plants happy (or at least alive) this summer!    

Rescued Butterfly Bush Finds A Home

Butterfly Bush Buddleia davidii

This Butterfly Bush (Buddleia davidii) was rescued from the discount rack at a local big box store that we call 'The Orange Store'.  It came in a tiny, flimsy plastic pot barely big enough for the roots, but only cost $2. It was wilty and sad looking at the time, but we saw promise in it because it had the best formed trunk and branches; no obvious evidence of girdling roots and several flower buds. 

When we brought it home, we put it in a spot under a California fan palm sapling (that will be transplanted too someday) and on the East side of the house to protect it from being blasted by the hot, setting sun each afternoon.  We transplanted it into two nested pots filled with a soil-less potting medium high in pearlite to ensure drainage and watered it until water began to drip from the bottom of the pot (it was sitting on a stand so that the water could drain out) every day.  

After it quit wilting, about two weeks later, it started to flower. The flowers sure are pretty! We are looking forward to seeing how it looks when the plant can support full inflorescences of blossoms.

Butterfly bush blossoms

The pink blossoms contrast nicely with the opposite leaves of this plant which are dark green on top (adaxial surface) and covered with fine, silvery white hair-like wax on the bottom (abaxial surface).  It may continue to produce pink blooms, or the next set might be a darker red, even almost purple as these plants have some variety in blossom color.  The flowers are quite small as seen above and are rather simple, yet elegant, in design with one row of petals, each with serrated edges, fused into a tube with a deep center that hides the pistil and stamens. 

Butterflies and hummingbirds possess tongues long enough to access the sweet nectar that these flowers produce.  We hope that this bush will become a natural feeder for them so that we'll get to enjoy watching them flit around the yard.  Since we never spray pesticides in our yard, we think we stand a better than average chance of attracting them now with this bush.


Once the bush flowered for a while (another couple of weeks) and even began growing new leaves (a very hopeful sign that it might survive after all), we decided to transplant it again.  The weather was cooperating too with highs in the 80's forecasted the whole week and a 40% chance of rain.  Cool, rainy weather is ideal for transplanting many species in the desert. 

To give the plant the best chance of success, we carefully planned its new location.  A well placed and well dug hole is the key to success when it comes to transplanting out here.

The ideal spot was between this wall

And this planter

We paced 7 ft from the wall to give the bush room to grow

This is a good spot because it will get morning sun, but afternoon shade from the house and it is close enough to my makeshift drip irrigation set up (someday, I'll install a proper irrigation system) that I can set a drip on it if I'm gone for an extended period.  It is also in a fairly level spot which will make controlling runoff much easier than planting on a slope.

Butterfly bush can grow to be about 15 feet wide and 12 feet tall, so we wanted a location where it would have plenty of room to grow without getting in the way of anything.  As you may have noticed from other blog posts, we are not big fans of needless pruning.  Had we planted this bush closer to the sidewalk or wall, it would need pruned almost annually.  Where it will be, it won't be too close to any of the traffic paths, and may even cast a little shade over the planter box someday. 

 

"Weed Barrier" is in the way!

Weed Barrier is a myth. It doesn't prevent weeds for more than a couple of years after installation.

Fine gravel under the plastic?

When we started digging, we discovered to our dismay, that the previous owners of this property had fallen for the myth that putting a layer of black plastic under your rocks would prevent weeds.  Apparently, they placed it over the entire yard.  We'd already removed some of it around the trees shortly after we moved in.  This plastic is going to have to go away if we can hope for healthy root systems for our plants.  It's preventing gas exchange between the soil and the air and is impeding water infiltration.

Good soil under the rocks

The soil profile of our yard. Note the compacted layer on the surface.

Now that we've gotten the rocks and plastic and compacted soil out of the way (please oh please dear reader, never cover your yard with rocks no matter what your water district says!), we've found actual soil.  We're blessed to have chosen a location in the Las Vegas Valley that has loamy sand soil with fine gravel! This is primo soil for the Mojave Desert. Very good drainage and just barely enough clay and loam in it to help hold moisture and nutrients.  Other places in the valley aren't so lucky and have layers of caliche 'clay' which is actually coral that was pulverized and buried when the volcanoes that are now the Black Mountains to the South erupted, burying what was once a huge lake as big or bigger than the Great Salt Lake to the North of us.  Where I am digging used to be part of the shoreline around that lake and is a bit more like digging in a beach than a lake bottom.  This is perfect for many desert native and adapted plants, including our little Butterfly bush.

I know this soil well, so I know what its physical and chemical properties are.  If I wasn't sure, I'd do a couple of tests before deciding to plop a plant in here.  First, I'd get a little vinegar and drip it in a shallow hole.  If it fizzed a lot, I'd know that the soil was very alkaline and may not be the best material to use for a plant species that is not adapted to the desert (such as roses or violets). Then, I'd dig a small hole down to my planned root zone depth and fill it with water, noting the time that I did so.  I'd come back every 10 minutes or so to check the water depth.  If the hole still had standing water in it after 30 minutes, I'd consider planting somewhere else or build a raised bed if there were no other good locations for the plant.  Never plant anything (other than maybe plants from swamps or marshes) in a place with poor drainage. Your plants will never be healthy there. 


We dug the hole down just as deep as the flower pot was and about four times as wide to be sure to get as much plastic and rock out of the way as possible.

Luckily, the pot happens to be as deep as a spade is tall....

Makes measuring hole depth easy

People used to think that digging a really deep hole was key, but research has found that most trees and shrubs do not grow a really long tap root that winds up being as deep as the tree is tall. Only a very short list of trees actually do that, most of which aren't even grown in the U.S.  Actually, the key to tree stability is lateral roots. A wide fan of lateral roots extending out beyond the drip line of the mature tree canopy is what keeps trees from falling over.  That's why one spade deep is deep enough for this bush, but we made it as wide as we could. Someday, we'll probably come back and dig up even more of the rocks and plastic and move them out of the way as the bush gets bigger. 

Gently tapping the rootball out of the pot...

keeps the roots from being damaged

 

Placing the rootball in the hole, ensuring that potting soil is under and on all sides of it

Since the Butterfly bush was grown in soil-less potting media, we chose to keep that around the roots and to line the inside of the hole with it.  Our soil is pretty good by desert standards, but it's good to keep as much of the original soil around the roots to avoid breaking off any more root hairs (the tiny, almost invisible parts of roots that do all of the water and nutrient uptake) than we have to.  Eventually, the roots will grow out of the potting media and into the native soil, so we made sure to avoid compacting the bottom and sides of the hole, even raking at the surfaces with our fingers to make sure the spade didn't compact the soil too much.  Smooth, firm holes just become underground pots, preventing future root growth.

The native soil was gently placed around and on top of the rootball and gradually sloping away from the trunk, leaving a gap about a finger's width around the trunk to help prevent stem rot.

Bare soil was then covered with wood chip mulch out to what will soon be the dripline

Now that the plant was in the hole, we gently placed native soil around the sides of the potting media pile and over the top of it up to about a finger's width of the trunk.  Then, we covered that with a two to three inch thick layer of wood chip mulch also within a finger's width of the trunk.  That will help reduce the chance of stem rot that sometimes happens when soil and mulch are piled up around the trunk.  The mulch will help keep the soil moist and reduce soil erosion.  We used such a thick layer to help prevent weeds and to keep the mulch in place better than a light scattering would have.  As the bush gets bigger, we will move more rock and plastic away from it and add more mulch in its place. 

We then irrigated the plant with about a gallon of water and will water it about every other day to prevent wilting.  Thanks to the good drainage of this soil, that won't water-log the roots.  In heavier clay soil or in caliche, we would have to wait longer between waterings to avoid drowning the roots.  If the soil was really tight, we would have just built a tall planting box full of potting medium on top of the ground with a reservoir hole filled with gravel underneath it and planted the bush in that.  Once the bush is established, a deep watering once a week will be all it needs, even in summer.   

  Now, if all goes well, no guarantees when it comes to growing things, we'll have a lovely Butterfly bush to enjoy for years to come.