You should schedule citrus pruning after February 15, the average last day of frost in Phoenix. Pruning can be done through mid-March, the aim being to wait to prune as long as possible to avoid frost damage, but before citrus blossoms set. Also if some fruit drops during pruning, it's usually sweet enough to eat. Heavy cutting back of certain shrubs and trees can be done during this time frame too. If pruned now, new growth will have time to harden off before hot weather arrives. You can still spray olives this month. Although light pruning can be done year-round on deciduous trees, early February is the last month for heavier crown reduction and thinning.
Now is the time to put down the first of four applications of citrus fertilizer (Feb/May/Aug/Oct).
Now is prime time for pruning most evergreen trees and shrubs. This is the last chance to prune citrus and ficus and other sun-sensitive trees. Be careful. If you wait too long, new foliage will not have time to fill in before sun damage occurs. As a rule, any area of bark exposed to direct sun for 3 or 4 hours needs to be protected with shade cloth or tree wrap to prevent sunscald. There are two general rules for pruning flowering trees and shrubs: For plants that produce blooms on old wood or last season's growth, prune as soon as possible after the bloom ends. For flowering plants that produce blooms on new wood or this season's growth, prune in late winter or early spring. March is a good month for fertilizing all trees. It's also a good time to apply a 2-3 inch layer of mulch around the base of trees and shrubs. This relatively inexpensive soil amendment does more to improve growing conditions around desert plants than any other treatment including fertilization. It reduces soil temperatures, runoff and evaporation, encourages nitrogen cycling and improves soil microbiology.
Now's the time to check your irrigation system for proper function and reset your timer for hotter temperatures. Increase duration, not frequency, of watering cycles as temperatures increase. It's better to water deeply and less often, especially if your trees are in turf settings. Be careful not to over-water though. It's a two-edged sword. It has been said that more trees die in Arizona of over-watering than under-watering. Ideally the root zone should dry out entirely between waterings. Avoid putting water on top of water. March and April are great months to plant citrus and most other trees as soil temperatures have warmed up and root activity increases. There may still be time to spray your olives, but you need to schedule soon.
May is a good time to prune trees to prevent storm breakage during summer monsoons in July and August. Alleviate end weight on heavy branches. Mesquite and eucalyptus trees are especially prone to wind damage. If your trees have been lion-tailed in the past, consider pruning them properly to alleviate end weight. Lion's tailing is an unacceptable pruning practice. It removes an excessive number of interior branches along the trunk and main branches. Not only are these smaller branches critical to protecting the tree from sunburn; they also help their host branches develop taper that is needed to support increasingly end weight as the tree matures. Trim date palms in May. If you wait another month, the dates will be larger and heavier and the clean-up and hauling is more difficult and expensive.
May is the month for the second application of citrus fertilizer. (Feb/May/Aug/Oct)
The heat of summer is the best time to plant and transplant palm trees. Trim Mexican fan palms after June 15th to be sure to get all the seed pods in one trimming. Trim Queen palms anytime after June 1st. Queen palm seed pods continue to emerge throughout the fall and winter, so the longer you wait, the more seed pods you will remove. There's still time to prepare for the monsoon winds by pruning larger trees. Consider installing staking systems on younger trees and adjusting systems on established trees. Proper staking should be strong enough to keep the tree upright in strong winds but loose enough to allow the trunk to move. This movement sends a message to the roots to get active in anchoring the tree. Like May, June is a great time to alleviate end weight on your trees before the monsoon winds arrive in July. As you'll see in the July/August section we recommend late summer pruning of mesquites and other vigorous tree varieties. Just be careful not to wait too long to prune them. If your trees look heavy, especially at branch ends, it may be best to prune sooner than later.
July / August
Life in the desert is on simmer. Monsoon storms are here now or due very soon. Batten down the hatches, adjust tree stakes and enjoy the rain! Watch a baseball game or escape to the mountains and listen to the wind whistle through the pine trees. Go Diamondbacks! Trim California fan palms after July 15th to insure getting all the seed pods in one trimming. If you don't want to put up with all the yellow pollen until July, you can prune the trees earlier, but you'll need to trim the trees again later in the year to get the rest of the seed pods. Prune mesquites and eucalyptus trees now if you haven't pruned them yet. There are two main reasons for summer pruning: First, these trees effectively compartmentalize pruning wounds, especially during this time of active growth so it's safe to prune in the extreme heat. Second, because they are near the end of their spring and summer growth, they "hold their prune" for more of the calendar year following the pruning. Keep in mind that the longer you wait to prune your mesquites, the higher the risk of wind damage during the monsoon.
August is the month for the third application of citrus fertilizer. (Feb/May/Aug/Oct)
If temperatures remain mild, you can safely prune most trees. Every year is a little different so watch the weather reports for changes from seasonal patterns. If there are warnings of an early cold snap, be careful not to prune frost-sensitive trees too heavily. You're taking away their winter coat! New growth that emerges after pruning is also more susceptible to frost-damage than older growth. October is a great month for planting and transplanting evergreens. There are also a few beautiful deciduous trees in the Phoenix area that give a brilliant display of fall color. One that does exceptionally well here is the Chinese Pistache (Pistacia chenensis.) To see a wonderful specimen, visit the Arizona State University campus just outside the main doors of the Agriculture building. This is also the month for the fourth and final citrus fertilizer application.
(Feb/May/Aug/Oct) Is the frost on the desert pumpkin? Probably not quite yet... back to top
As temperatures begin to drop, lighten up the pruning on most evergreen trees except for deadwood removal and structural improvements. For more vigorous trees like mesquites, olives, sumacs and eucalyptus, a little more pruning can be done. In fact we recommend a semi-annual light pruning of trees pruned in May or June. Because most mesquites can't safely go a full year on their summer trimming, it makes sense to prune them again now. This semi-annual interval also has the benefit of readying the trees for the holiday season. It's a great time to begin or add to a compost pile with all your raked leaves and other fall yard waste. By early spring you'll have the best top dressing and potting soil around. If you plan to put up lights for the holidays, it's helpful to prune your trees ahead of time. It makes removal of the lights easier too. Also, don't nail or staple wires to branches. Use gardening tape or twine instead. And to prevent girdling of branches, remove lights from trees after use. back to top December Citrus fruits begin to ripen now. Change in color is due to cooler temperatures but may not always indicate sweetness. Deciduous trees should be pruned now through February. These include mulberries, pecans, elms, ash, desert willows, chaste trees, stone fruits and others. Shrubs like Mexican bird of paradise, lantana, yellow bells, orange jubilee, bougainvillea, oleander and cassia can be cut way back.
As in November, December
A great time to remove deadwood from any tree. It's also a good time to plant or transplant deciduous trees. Deciduous trees planted on the south side of a house provide summer shade but allow sunlight through during winter when the leaves are off. Happy Holidays!