The seven layers of a food forest in the low desert

Why layers, and why they matter more in the desert

A natural forest does not plant in rows. Tall trees shade smaller trees, shrubs fill the gaps, herbs and ground covers close the surface, vines climb whatever is standing, and roots work the ground at every depth. Nothing is wasted because every layer is using something the others leave: a different band of light, a different depth of soil, a different season.

In the low desert the stack is not a nicety. Summer sun and bare soil are what kill young fruit trees here, and the fix for both is other plants. A canopy tree cuts the afternoon heat. A covered soil surface keeps water in the ground. Get those two layers right and the five in between become possible on a Phoenix water bill.

The planting planner files every plant in its catalog under one of these seven layers, so the list below is the same list you will use when you place them.

1. Upper canopy

The tallest trees on the lot, and the first thing to decide. In most climates the canopy is about food. In the low desert it is about shade first: a Phoenix yard in July is a different place under a mesquite than it is in the open, and nearly everything below this layer only survives because of it.

Natives do the job best here. Mesquite, palo verde and ironwood grow fast on little water, drop fine litter that becomes mulch, and fix nitrogen in the soil through their roots. A large mulberry or a pecan does the same for shade and adds a harvest, at the cost of more water.

Shade. Knocks the afternoon sun off everything underneath and cools the house and the soil.
Nitrogen. Mesquite, palo verde and ironwood are legumes. Their roots feed the soil for every plant nearby.
Mulch and habitat. Leaf and pod drop builds the soil surface, and the canopy holds the birds and insects the lower layers need.

2. Lower canopy

The fruit trees, kept below the tall ones. This is where most of a home food forest's harvest comes from: figs, pomegranates, jujubes, peaches, apples, plums and the citrus that grow so well in the Valley. The trick in the desert is to keep them small on purpose. A fruit tree held to eight or ten feet with summer pruning is easier to net, harvest and water, and it fits under the canopy that protects it.

Place them where they get morning sun and some relief from the west. Under or just east of an upper-canopy tree is usually the right spot.

Fruit. The main harvest of the system, timed across the year by choosing varieties that ripen in different months.
Second shade. A lower, denser shade that cools the shrub and herb layers and the soil they grow in.
Structure. Trunks and branches for the vines to climb and for the birds that keep pests down.

3. Understory & shrubs

Woody plants at head height and below. They fill the space between the trunks and the ground, which in a bare desert yard is where the heat and the wind come in. Fruiting shrubs such as blackberries, blueberries in a pot of acid soil, pineapple guava and Barbados cherry give a harvest at an easy height. Native shrubs such as yellow bells, Texas sage and hopseed give flowers, screening and the thickets that birds nest in.

In the low desert a few fruit trees are better grown as shrubs. A pomegranate or a fig left as a multi-stem bush at six to eight feet is easier to protect and picks clean.

Berries and small fruit. A harvest at arm's reach that starts producing years before the trees do.
Pollinators. Long bloom seasons for bees, butterflies and hummingbirds, which the fruit trees depend on.
Shelter. Windbreak, privacy and nesting cover, and a softer edge along walls that otherwise radiate heat.

4. Herbaceous

Soft-stemmed plants that die back and return: kitchen herbs, perennial greens, artichokes and asparagus, and the flowering perennials that keep the pollinators coming when nothing woody is in bloom. This is the layer you visit every day, so it belongs close to the kitchen door, in the shade of the trees above it.

In the desert the herbaceous layer runs on two calendars. Cool-season greens and herbs go in from October and carry through spring. The tough perennials, globe mallow, desert milkweed, the mallows and the sages, hold the ground through summer.

Daily food. Greens, herbs and perennial vegetables, harvested a handful at a time.
Pollinators and pest control. Flowers through the year bring the bees, and the insects that eat the ones you do not want.
Living mulch. Leaves shade the soil, and what dies back in summer feeds it.

5. Soil surface

Living ground cover and the mulch it grows through. In the low desert this is the layer that decides whether the whole thing works. Bare soil here reaches well over a hundred degrees at the surface and sheds water instead of taking it in. Covered soil stays cool, holds moisture between waterings and keeps its biology alive.

Start with wood-chip mulch, four inches deep, over every basin and bed. Then plant low spreaders into it: trailing herbs you can walk on, native daisies that reseed, and a lawn alternative such as Kurapia where you want something to sit on.

Water. Covered soil loses far less to evaporation, so the same irrigation goes further.
Soil. Mulch and roots feed the fungi and worms that turn desert dirt into soil.
Weeds and heat. A closed surface leaves nowhere for bermuda to start and keeps the root zone cool.

6. Root layer

What is happening underneath. Deep taproots, the mesquite's most of all, open the soil and pull water up from well below the irrigation. Shallow feeder roots take what the trees leave. And the root crops, carrots, beets, garlic, onions and potatoes, hold their harvest underground through the cool season, which is the only season they want here.

This layer is also the argument for not tilling. Once the fungal network between the trees is established, every spade cut through it costs the system something. Plant the root crops in their own beds at the edge and leave the ground under the trees alone.

Underground harvest. Root crops sown in fall, pulled through winter and spring before the heat.
Soil structure. Taproots break caliche and compacted ground and leave channels water can follow.
Sharing water. Deep and shallow roots use different water, so more plants fit on the same irrigation.

7. Vining

Climbers that use somebody else's structure for height. Grapes on a wire trellis along a wall, passion fruit over a seating area, dragon fruit up a post, a native yellow orchid vine along the block fence. A vine produces on almost no ground, which in a small yard is the point, and a vine on a west-facing wall is the fastest shade you can build.

Give each vine the structure first. A mature trunk, a cattle panel arch, a pergola or a fence all work. Keep grapes off the fruit trees until the trees are large enough to carry them.

Fruit without footprint. Grapes, passion fruit and dragon fruit from a strip of ground a foot wide.
Shade on walls. A leafy vine cuts the heat a west wall throws back at the yard and the house.
Flowers. Native vines bloom for months and feed hummingbirds and bees along fences nothing else uses.

How the layers stack

Seen from the side, a food forest is a set of bands that narrow as they go down, with the soil surface running under all of them and the roots below that. The vine runs up the side using whatever is tallest.

Upper canopyMesquite, palo verde, ironwood, pecan: sets the shade for everything below.
Lower canopyFruit trees held to eight or ten feet, under and east of the tall trees.
Understory and shrubsBerries, pomegranates, native flowering shrubs in the gaps between trunks.
HerbaceousHerbs, greens and perennial flowers close to the door.
Soil surfaceMulch and living ground cover over all of it.
Root layerTaproots, feeder roots and the root crops, all working different depths.

Plant the top and the bottom first. A canopy tree and four inches of mulch on the first weekend make every layer in between easier for the next ten years.

Plan yours on a map of your yard

Type your address and the planting planner opens on an aerial of your lot. Place canopy trees at their mature width, tuck the fruit trees under them, and the planner names each plant's layer as you go. No account needed to start.

Want a second pair of eyes on the plan?

Whether you are planting all of it yourself or hiring as much as possible, tell us about your property and we will set up a free discovery call. We will look at your layers, your water and your shade before you buy a single tree.

The seven layers of a food forest