If you’ve got an orange, lemon, grapefruit, or lime tree in your Phoenix backyard, September is one of the most important months of the year for citrus health — even though it doesn’t look like much is happening. After a brutal summer, your citrus tree has been quietly working overtime just to survive the heat. Now, as temperatures start to ease, it’s shifting into a new phase: storing up the nutrients it will need to bloom and fruit well next year.
Get this month right, and you’re setting up a stronger, more productive tree for spring. Skip it, or make a few common mistakes, and you could end up with yellowing leaves, weak fruit set, or a tree that struggles through winter.
Here’s exactly what your citrus trees need this September — and just as importantly, what to leave alone. If anything below turns up a problem your tree can’t fertilize its way out of, our certified arborists are always a call away. leave alone.
Not sure where to start? Request a free tree health consultation with our certified arborists today.
Citrus trees in the low desert are heavy feeders, and Arizona’s soil doesn’t make it easy on them. Our native soils are naturally low in nitrogen and iron, and the intense summer heat burns through whatever nutrients were available even faster. By late summer, most citrus trees have used up the reserves from their spring and early-summer feedings.
September fertilizing is typically the third and final feeding of the year for Arizona citrus, following applications in late winter and late spring. This fall application does two jobs at once:
Skip this feeding, and your tree heads into winter running on empty — which often shows up as weak spring flowering or smaller fruit the following year.
Citrus trees need more nitrogen than most other landscape trees, along with iron and zinc to prevent the yellowing (chlorosis) that’s so common in desert soil. Look for a fertilizer labeled specifically for citrus, and apply it according to label rates based on your tree’s size and canopy spread — more is not better, and over-fertilizing can burn roots or push out weak growth right before cooler weather arrives. If you’re not sure whether the issue is nutrients or something happening below the surface, our soil treatment specialists can test and correct what your tree is actually dealing with.
Apply the fertilizer evenly under the tree’s full canopy (not piled against the trunk), then water it in thoroughly so the nutrients move down into the root zone where they can actually be used.
September in Phoenix can still bring 100-degree days, but the cooler nights mean your citrus tree’s water needs are starting to change. Deep, infrequent watering is still the goal — water should soak down 2 to 3 feet and extend out to at least the edge of the canopy, since that’s where the feeder roots are concentrated. As temperatures continue to drop through fall, you’ll gradually stretch the time between waterings. For a closer look at proper depth and timing, the University of Arizona Cooperative Extension’s Irrigating Citrus Trees guide is a great reference — or our irrigation team can evaluate and adjust your system for the season.
A 2- to 3-inch layer of organic mulch, spread out to the edge of the canopy (and kept a few inches away from the trunk itself), helps regulate soil temperature and lock in moisture as the season transitions. If your mulch has broken down or thinned out over the summer, September is a great time to top it off.
Take a walk around your tree and look at the leaves. Yellowing between the veins while the veins themselves stay green is a classic sign of iron deficiency, which is extremely common in Arizona’s alkaline soil. Overall pale or yellow foliage, on the other hand, often points to a nitrogen shortage. Catching these signs now — before your fall fertilizer application — helps you choose the right formula and correct the problem before it affects next year’s fruit.
This is the one mistake we see most often. Unlike many landscape and shade trees, citrus trees should generally be pruned in spring, not fall. Pruning now can trigger a flush of tender new growth right as temperatures start to cool — growth that’s far more vulnerable to any early cold snap. If you spot dead, broken, or clearly diseased wood, it’s fine to remove it, but hold off on any real shaping or thinning until spring.
It’s tempting to think of fall as wind-down season, but citrus trees are still very much active below the surface. Skipping this feeding because it feels late in the year is one of the most common reasons Arizona citrus trees underperform the following spring.
If your tree looked stressed over the summer, resist the urge to compensate with more frequent watering now. Citrus trees are far more likely to suffer from root problems due to overwatering and poor drainage than from underwatering, especially as temperatures cool and the tree’s water use naturally drops.
Sometimes yellowing leaves, fruit drop, or slow growth are about more than a missed fertilizer application. Soil compaction, poor drainage, root issues, or pest activity can all mimic nutrient deficiency symptoms — and treating the wrong problem can waste months of the growing season. If your tree isn’t responding to fertilizer and proper watering, it’s worth having a certified arborist take a look at the soil and root zone before the problem carries into next year.
Seeing signs your tree can’t fix on its own? Schedule a tree health assessment before the problem carries into spring.
Citrus trees are one of the true perks of living in the Valley — but they need the right care at the right time to keep producing fruit year after year. A well-timed September feeding, a healthy watering routine, and a keen eye for early warning signs are the difference between a citrus tree that limps through winter and one that rewards you with a great harvest next spring.
If you’re not sure what your tree needs, or you’re seeing yellowing, leaf drop, or stunted growth that fertilizer alone isn’t fixing, our certified arborists can assess your soil, roots, and overall tree health and put together a treatment plan built for your specific tree. Request a consultation with PROS Tree & Landscape today.
Should I fertilize my citrus tree in September in Arizona? Yes. September is typically the third of three annual fertilizing windows for Arizona citrus trees (after late winter and late spring), helping the tree store nutrients for winter and next year’s bloom.
Can I prune my citrus tree in the fall? It’s best to avoid major pruning in fall. Citrus trees are typically pruned in spring; fall pruning can encourage tender new growth that’s vulnerable to cold. Removing dead or damaged wood is fine any time of year.
Why are my citrus tree’s leaves turning yellow in September? Yellowing between green veins usually points to iron deficiency, while overall pale foliage often signals a nitrogen shortage — both common in Arizona’s alkaline soil. It can also indicate overwatering or root stress, so it’s worth investigating if fertilizer doesn’t resolve it. Contact PROS Tree & Landscape to see exactly what your trees need. 
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How much should I water my citrus tree in the fall? Water deeply enough to soak 2–3 feet down and extend to the edge of the canopy, then gradually increase the time between waterings as temperatures drop through fall.
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