Winterizing trees in the low desert
Winterizing Trees in the Low Desert: A Practical Guide for Phoenix to Tucson Homeowners
While our winters are mild most of the time, those sudden radiational freezes (28 °F down to 22 °F for a few hours) in December–February can cause serious damage to fruit trees and cold-tender ornamentals—especially citrus, young deciduous fruits, Ficus, sissoo, and other subtropical species. This guide is written for homeowners, DIY gardeners, and anyone who wants to keep their trees healthy and productive without expensive professional intervention every year.
Which Trees Actually Need Your Attention in the Low Desert?
Almost all damage happens to:
Citrus of any kind (lemons and limes are the most sensitive, followed by grapefruit, mandarins, and oranges; kumquats and calamondin are slightly hardier)
Very young pomegranates (<1 year old) and young figs
Young low-chill deciduous fruit trees (peaches, nectarines, plums, apricots, apples, pears) – mature trees are usually fine once dormant
Avocados and mangoes grown in protected microclimates (very frost-tender)
Cold-sensitive ornamentals: Ficus (all species), Sissoo, Shoestring Acacia (young), Tipuana tipu, Texas Mountain Laurel (young), some Eucalyptus species, Queen and Pygmy Date palms, Bottle trees (Brachychiton)
Once established (5+ years) and properly sited, pomegranates, figs, jujubes, and most low-chill stone fruits almost never need freeze protection in the Phoenix–Tucson corridor. The trees that get hurt worst are citrus, young fruit trees, and the ornamental subtropicals listed above.
General Winter Practices That Protect Every Tree
These steps alone will get you through 90 % of our winters and dramatically reduce damage when it does get cold.
A. Keep Watering – Don’t Go Dormant on Irrigation Dry soil radiates heat away rapidly on clear, cold nights.
Citrus & evergreen ornamentals: Deep water every 2–3 weeks if no rain.
Deciduous fruit trees (bare in winter): Every 3–4 weeks.
Newly planted trees (<2–3 years): Every 10–14 days. Always water deeply the day before a freeze forecast.
Remember to actually check soil for moisture! Often overlooked, continuing to water too frequently leads to pathogens and rot.
B. Mulch Heavily 3–4 inches of coarse organic mulch (arborist chips, shredded bark, or stall fines) out to the drip line, kept 6 inches from the trunk. This is the single best root insulator we have in the desert. Top it up every November for good measure. This keeps the roots warm over clear, cold nights. Remember not to pile organic matter against the trunk, which is common practice in over-wintering some trees. This leads to basal crown rot or fungal growth.
C. Wrap Young Trunks – Mandatory for Thin-Barked Trees Our bright winter sun + cold nights = sunscald and frost cracks on the southwest side. Wrap smaller, less established trees, and those that may already be or become stressed due to environmental factors (most citrus under 4 years, young stone fruits, sissoo, ficus, avocados, etc.). Use commercial tree wrap, burlap, or even light-colored cardboard tubes. Install Thanksgiving weekend, remove mid-March.
D. Pruning Timing
Deciduous fruit trees (peaches, plums, apples, pears, pomegranates, figs): Winter pruning is ideal – do it December–January while dormant.
Citrus: Wait until late February or March after the last freeze risk for anything beyond light shaping. Heavy pruning now pushes tender new growth that will burn in the next freeze.
How to Handle a Hard Freeze Night (28 °F or Lower for 3+ Hours)
These are the exact steps I use on my own trees and my clients’ high-value trees.
Monitor reliable forecasts I use the NWS Phoenix/Tucson detailed forecast, Pima & Maricopa County Ag Extension alerts. Act when lows are forecast ≤28 °F for more than 2–3 hours.
Water deeply the afternoon before.
Cover completely to the ground (most important for trees under 8 ft) Best: 1.5–2.0 oz frost cloth (N-Sulate, Agribon, Planket) – reusable for a decade. Good backup: Old blankets, sheets, burlap (double layer if very cold). NEVER plastic touching the foliage – it conducts cold and causes more damage. Secure edges with rocks, bricks, or soil to trap ground heat.
Add heat under the cover for nights below 27 °F Incandescent C7/C9 Christmas lights (the old big bulbs, not LED) are still the gold standard. Two to three strings on a mature citrus tree can raise temps 8–12 °F under cloth. Alternative: 100-watt equivalent outdoor LED work light (still produces some heat) or multiple strings of incandescent rope lights.
Extra measures for very young or high-value trees
Wrap trunk in bubble wrap or pipe insulation underneath tree wrap.
Place gallon jugs of hot water under canopy at dusk, then cover.
Trunk-wrap with incandescent lights for graft or bark-crack protection on citrus.
Uncover promptly in the morning Remove covers as soon as temps are above freezing and sun is fully up. Leaving them on too long causes heat buildup and foliar burn if using electrical measures and multiple layers.
After the Freeze
Leave brown leaves and twigs alone – they insulate against the next event.
Do not prune anything until mid-April or when you see solid new growth pushing.
Most citrus and deciduous fruits recover remarkably well from undamaged wood even after looking 80–90 % dead.
Bottom Line From Your Local Arborist
The trees that lose crops or die in Valley freezes are almost always the ones that were dry at the root zone, newly planted, or completely exposed on a clear, cold night. A $40 frost blanket, a string of old Christmas lights, proper watering, and trunk wrap will save you thousands in replacement costs.
Get these habits in place now (early December is perfect timing), and your citrus will keep fruiting, your young peaches will make it to maturity, and your ficus and sissoo won’t split or defoliate every few years.
Happy (and warm) gardening!
