Desert Landscaping in Phoenix: Why Fall Is Planting Season and How to Water in Winter

In the Phoenix area, fall is the best time to plant most desert landscape plants. The soil is still warm, which helps roots grow, and cooler days mean new plants need less water. Once winter sets in, most desert plants need far less irrigation than in summer, so cutting back your timer is one of the easiest ways to save water.

When people move here from places with green lawns and spring planting, the desert yard can feel backwards. Here is what I share with new homeowners, based on guidance from local water providers and the University of Arizona.

Why Fall Beats Spring for Planting in the Low Desert

The Water - Use It Wisely campaign, run with Valley city water departments, puts it simply: fall in the low desert is the ideal time to plant. Our spring is short and runs straight into early summer heat. A tree planted in April has only a few weeks before 100-degree days arrive, while a tree planted in October gets a full cool season to push roots out into the native soil.

That root growth matters. A plant from a 5- or 15-gallon pot needs time to spread roots beyond the shape of the container before it faces its first summer. Warm fall soil encourages that growth, and the cooler air means the plant is not losing as much water through its leaves.

There are a few exceptions. The same campaign notes that bare-root plants such as roses, pecans and fruit trees are usually planted in late December or January while they are dormant, and palms and other tropical plants do best when planted in spring or summer.

How to Water New Plants This Fall

According to Water - Use It Wisely, newly planted plants put in between fall and spring can be watered about once every 3 to 4 days at first. As they settle in, gradually stretch out the number of days between waterings.

Mulch helps too. The campaign suggests adding 2 to 3 inches of compost or organic mulch after planting, before any granite or rock goes on top, and keeping it a few inches away from the trunk or stem. University of Arizona Cooperative Extension adds that a 3 to 4 inch mulch layer can significantly reduce how often you need to water, and it advises against putting plastic under mulch.

Winter Watering: Deeper, but Much Less Often

The Arizona Municipal Water Users Association (AMWUA) says many homeowners keep watering through winter as if it were still 110 degrees outside. Most desert-adapted plants need little or no water in winter, and soggy soil can actually harm roots.

Here is the general approach AMWUA recommends:

• Water deeply. Aim to wet the soil about 3 feet deep for trees, 2 feet for shrubs and 1 foot for groundcovers. A soil probe or a sharpened dowel pushed into the ground shows how far the water reached.
• Water less often. Desert trees such as palo verde, mesquite and acacia generally need a good soaking about once a month in winter. Other trees, about every two to four weeks.
• Turn the timer off after a good rain. After a heavy rain or two, you can shut off irrigation for a while.
• Still run the system now and then. Turn it on for a couple of minutes at least once a month to catch leaks and broken emitters.

AMWUA also offers a free monthly reminder: text WHENTOWATER to 33222 and you get a link to a watering guide for that month.

University of Arizona Extension notes that plants use three to five times as much water in hot, dry, windy months as they do in winter. It also recommends watering at the drip line (the outer edge of the canopy), not right against the trunk, since roots spread well beyond the canopy.

Protecting Plants on Frosty Nights

AMWUA suggests keeping frost cloth on hand, draping it all the way to the ground rather than wrapping a trunk, and removing it during the day when you can. Potted plants can move under a patio cover, an eave or into the garage.

Two other winter tips from AMWUA: do not fertilize in winter, because it pushes tender new growth that cold can damage, and do not cut off frost-damaged parts right away. Wait until late February or early March to trim. For cactus, AMWUA says they tend to suffer less frost damage when they have not been watered for several months before cold weather, because water freezing inside the plant can rupture its cells.

If you have citrus, I covered frost protection for those trees in more detail in my post on citrus trees in Arizona.

Thinking About Replacing Grass?

Many Valley cities encourage swapping thirsty lawns for desert landscaping. The City of Phoenix, for example, runs a Residential Grass Removal Program for property owners who are Phoenix Water Services customers. Pre-approval is required, and grass removed before the city issues a Notice to Proceed is not eligible, so read the rules before you start digging. The city says choosing desert plants can lower outdoor water use by 85% compared to grass.

If you live in another city, check your own water provider's website, since programs and rules vary. For plant ideas, AMWUA keeps a searchable desert plant list at amwua.org/plants.

What I Tell Buyers Looking at Desert Yards

When I tour homes with buyers, I look at the landscaping as part of the house. A few things worth checking: whether drip lines reach the edge of each tree canopy, whether the timer is set for the season, signs of leaks such as soggy spots or extra green weeds, and big trees planted too close to the house or pool. These are good questions for your inspection period, which I explain in my home buying guide. And if your water leaves white crust on emitters and fixtures, my post on hard water in Phoenix explains why.

For more on settling into the Valley, see my Moving to Phoenix guide and the cost of living in Phoenix page.

Questions People Ask

When is the best time to plant in Phoenix?
For most desert trees, shrubs and groundcovers, fall is the best time to plant. Warm soil helps roots grow and cooler weather lowers water needs. Palms and tropical plants are an exception and do better planted in spring or summer.

How often should I water desert trees in winter?
Much less than in summer. AMWUA says desert trees like palo verde, mesquite and acacia generally need a deep soaking about once a month in winter, and other trees about every two to four weeks.

How deep should I water trees and shrubs?
AMWUA recommends wetting the soil about 3 feet deep for trees, 2 feet for shrubs and 1 foot for groundcovers. A soil probe or long screwdriver shows how far the water went.

Should I fertilize my desert plants in winter?
No. AMWUA advises against winter fertilizing because it forces tender new growth that frost can damage. Mulch is a better winter choice.

Terry Day, REALTOR®, DeLex Realty, 10115 E Bell Rd, Scottsdale, AZ 85260.