The University of Arizona

College of Agriculture and Life Sciences

Improving Lives, Communities and the Economy

Free Plant Clinic - Pima County Master Gardeners

Master Gardeners are available to answer your gardening questions over the phone, on a walk-in basis or online. There is no charge for this service. There is also a wall of resources and handouts in the Plant Clinic that are available to the public. Call, stop by or email us today!

Tucson 520-626-5161 4210 N Campbell Avenue Tucson, 85719 Monday-Friday 8:30am-4:30pm

Southern Pima County 520-648-0808 1100 E Whitehouse Canyon Rd, Green Valley, 85622 Monday-Friday 8am-12pm
Submit a question online here

Below are some of the most commonly asked questions by home gardeners in Pima County, Arizona For more details, or for answers to questions not listed here, call or visit the Master Gardener Plant Clinics during the hours listed above.

  • How do I prune my citrus trees?

The general rule for pruning citrus trees is DON'T. Only prune dead or crossing branches and a wayward branch. Do not prune in the summer; you could leave branches or trunk exposed to the sun which may cause sunburn. Never prune more than 15% at one time.

  • How do I fertilize my citrus trees?

Citrus are usually fertilized three times a year - For oranges, tangerines, and grapefruit, use 1/3 the recommended annual amount in Jan/Feb, 1/3 in Mar/Apr and 1/3 in May/June.  For lemons and limes, use 1/3 the recommended annual amount in Jan/Feb, 1/3 in Mar/Apr and 1/3 in Aug/Sept.. Newly planted trees do not need fertilizer the first 1-2 years. Use Ammonium Sulfate, Ammonium Phosphate or Citrus Food fertilizer. The amount of fertilizer needed per year depends on the age, the size, and the type of tree. For example, a medium-sized adult tree 5-6 years after planting needs 6.2 pounds of Ammonium Sulfate per year (split into three applications). Grapefruit trees 5 or more years after planting need half the amount for other citrus.

  • How big should I dig my planting hole?

Dig a hole three to four times as wide and the same depth as the rootball. Do not disturb soil at bottom of the hole. Fill planting hole with water and allow to drain. Fill again. Water should drain in about 24 hours. If it hasn't, try another site, create a drainage chimney, or consider a raised bed. Remove plant from container; slice the outside of the rootball if rootbound. Set in planting hole with top of rootball one inch above the surrounding soil level. Fill hole with soil dug from the planting hole; no need to add amendments. Water thoroughly to settle soil. Build a soil basin or install sufficient drip emitters. Add 3 to 4 inches of mulch over the root area to conserve moisture.

  • Where can I get a soil test?

Soil tests are generally not necessary in this area. Our soils are typically highly alkaline and very low in organic matter.

  • The leaves disappeared from my plants overnight. What happened?

Leafcutter ants will collect leaves for the fungus farms. Ants are a vital part of our desert ecosystem and in most cases damage is tolerable. Usually your plant will leaf out again and be fine. Ant poisons and bait are not effective; set up a physical barrier such as a tree wrap or Tangle foot to minimize damage.

  • My roses and bougainvillea have round holes cut in the leaves? What caused it?

Solitary leafcutter bees remove circles of leaf to build nests for their young. The harvesting does not endanger the health of the plant.

  • My plant's leaves have brown edges. What is the problem?

Brown edges are often a sign of salt damage; the salt contents in our tap water can cause the damage and is often compounded by insufficient water. Thoroughly water the plant (shrubs to 2 feet deep; trees to 3 feet deep) to leach excess salts away from the roots.

  • What advice can you give me about watering?

Correct watering depends on many factors. For advice, call our Master Gardeners at 626-5161 or check out the Master Gardener Manual chapter on irrigation at the following website: For example, in general shrubs need to be watered every 5 to 14 days in the summer. Watering should be done deeply and infrequently: lawns & cacti to a depth of 12 inches; flowers & vegetables to a depth of 18 inches, shrubs, hedges & vines to a depth of 24 inches' and trees to a depth of 36 inches.

  • There's a white fuzz on my cactus. What is it?

The white fuzz is a protective coating produced by a tiny insect called Cochineal Scale. Wash the insects off with a strong stream of water.

  • How do I get rid of weeds?

Many weeds can be controlled with a pre-emergent to prevent weed seeds from germinating and growing. Remove weeds when they are small by hand-pulling or hoeing. Entrenched weeds can be removed with a glyphosate herbicide (such as Roundup). NEVER use strong weed killers (labeled as brush and stump remover, driveway & sidewalk killer etc.) or soil sterilants such as TRIOX or GROUND CLEAR.