Saturday, September 3, 2022

Create your own Sonoran Desert Food Forest

Richard Roati's food forest

There's nothing like having a lush canopy of trees to enhance your life in the desert. Those trees won't just cool your house and yard (and cut down on your energy bill), but they will help cool off the whole neighborhood. Areas with trees are up to 12 degrees cooler than areas without. And those tree branches hanging over sidewalks make a nice place to walk your dog and socialize with your neighbors. 

You've probably seen gravel and cement in too many yards around town. While that may cut back on the water that would otherwise have been used for a lawn, that cement holds in the heat contributing to the heat island effect. Phoenix, with all its asphalt and cement, doesn't cool off at night! That's dangerous for plants, animals and people. Planting trees helps mitigate the heat island effect.

So...we need more trees in Tucson. But what about the water shortage in the desert? How are we supposed to water all those trees? I suggest we embrace our desert surroundings and plant low water, drought tolerant native trees with rainwater harvesting catchment basins. Native trees take little or no water once established. They include ironwood, palo verde, and velvet mesquite (not to be confused with non-native Chilean mesquite trees that grow too quickly and have been known to fall over during a storm.)

You can learn how to build your own basin at the free Rainwater Harvesting Rebate Classes offered by Watershed Management Group or S.E.R.I

Here's how my husband Dan (a docent at WMG) made our front yard basin...

First, he dug up two feet of  gravel and pulled plastic out of our yard.

Then he observed where the water flowed when it rained. He noticed that an awful lot of water was coming off the side of the roof and was causing erosion where it fell. So he dug a shallow basin in the middle of the yard using that dirt to build up a small berm with a gradual slope so the roof water would flow at least ten feet away from the foundation of our house and into the basin. (The idea is to slow down and spread out the water so it sinks in.)

Because they are on the south side, he planted three native trees far from the house on the high end of the basin. Then he planted some native bunch grass in the bottom of the basin and filled it with woodchip mulch. The roots of the grass along with the woodchip mulch create a sponge to hold the water longer. As the woodchips breakdown they provide organic matter to the soil that in turn nourishes those trees. How cool is that? 

Did you know that those native trees are also edible?  The ironwood and palo verde have yummy seeds. And dried mesquite pods can be ground into a delicious and healthy flour. As long as we have these edible trees, why not just go ahead and create a desert food forest? If you're gonna use water for a tree, you might as well plant something you can eat, right?  But creating a desert food forest provides much more than shade and nutritional food for your family and neighbors. If you do it right, it will provide a fine habitat and food for local birds and flowers for pollinators. And that makes it a lovely place to hang out.

Dan also created a little mesquite guild in our front yard by planting a hackberry bush under the mesquite tree. The mesquite acted as a nurse tree protecting the young hackberry from the sun. It also added nitrogen to the soil. Nearby is a prickly pear cactus that has edible pads and fruit! 

This year we got to try our first berries. The little orange berries tasted like a combination of cantaloupe and cucumber. The birds enjoy them too. 

In our back yard, we took advantage of our outdoor washing machine to irrigate low water heritage fig and pomegranate trees in our greywater basin.  Heritage trees are ones that have been here so long that they have adapted to our climate. 

Watershed Management Group also offers greywater classes. 

But my favorite rainwater harvesting feature has to be our jujube basin. We already had gutters and a downspout in place.

So Dan dug a long basin with three mounds along it where he planted jujube trees.  Native bunch grass serves to slow down and sink in rainwater, hold the mulch in place and prevent erosion. Jujubes are a Chinese fruit that look like little apples. Although they aren't traditionally from Tucson, we have found that these trees are really drought tolerant with their shiny leaves. I only watered them every other week in the hottest month of June. And I didn't water them at all during the rainy season. This is how they are doing now....

Coming from another part of the country, the first thing many people want to do is plant their favorite fruit trees from home. Totally understandable. Just do a little research and find out how much water those trees need so you don't overwater or underwater them. Find out how to take care of them in the desert. They may need some shade from our brutal summer sun and mulch to keep the moisture in the ground longer. Come up with as much water as you can from greywater (washing machine, bathwater, air conditioner condensate) and rainwater harvested from the roof. Take care of those trees, because when a tree dies in the desert all the water that went into it is lost too. 

Our friend Richard Roati has several big fruit trees in his yard. To offset his water use (and water bill) he has two big cisterns that collect water off of his roof. And he has hooked up water from his bathtub and his outside washing machine. All that water supports his citrus trees, carob, and jujubees. He has also started a nursery of native plants (including agave and cactus) that he has rescued in his neighborhood. We actually got our three jujube trees from him! Thanks, Richard! 

It's important to plant foods that your family will enjoy to prevent food waste and loss of all the water that goes into it. If you already have some fruit trees in your yard that you aren't gleaning, you can always call our local treasure Iskashitaa Refugee Network to come harvest them and prevent food waste. 

In conclusion, here are some recommended ways to put in your Desert Food Forest. 

1) Plant edible native trees and plants with rainwater harvesting (mulch covered) catchment basins. 

2) Plant low-water heritage fruit trees in basins with greywater from your washing machine, air conditioner and/or bathtub. Supplement that with rainwater from your roof directed to cisterns (water barrels). 

3) Plant durable, drought tolerant fruit trees in basins with water directed from your roof supplemented with some rainwater collected in cisterns (large rain barrels.) 

4) Plant a few of your favorite fruit trees that you can maintain with roof and greywater (maybe supplemented with very little city water.) 

To be really sustainable, it is important to calculate how much water you get off of your roof and various greywater sources and then plant only what you can maintain on that budget. 

Watershed Management Group has a calculator you can use:

https://watershedmg.org/water-budget-calculator

Like our friend Richard (pictured above) we do a combination of these four approaches in our edible desert forest.  

You can read more with Richard Roati in Exploring food forests in Tucson by Elena Acoba.

Check out the Mayor's Million Trees program