September: What to Do in the Desert Garden

September means the monsoon is winding down and even though it might be fall elsewhere, it’s still summer here. There’s plenty to do in the garden this month. Here’s a look at what you should and shouldn’t plant, what you can fertilize, pests to expect, fruit you can harvest, and more.

Summer is winding down and the monsoon officially ends at the end of the month. As the average temperature cools down slightly, garden activity ramps up. After months of merely trying to keep your plants alive, plants and gardeners experience a little relief this month.

September Weather Outlook

Even though it may feel like fall will never arrive, there is some progress on the weather front. September is a little cooler and dryer than August. The average evening low in Tucson is a delightful 70°F… nice! 😉 The days are getting noticeably shorter and the sun continues to get less intense.

Here’s a look at September weather averages in both Tucson and Phoenix.

September Weather Averages (Tucson)

High temperature	95°F
Low temperature	70°F
Precipitation	1.28″
Relative humidity	39%
UV Index	9.0
Wind	14 mph

September Weather Averages (Phoenix)

High temperature	101°F
Low temperature	78°F
Precipitation	.59″
Relative humidity	29%
UV Index	8.2
Wind	7 mph

If you live elsewhere, enter your city or town in the search bar at TimeandDate.com to find your monthly averages. You can find your average UV index at UVIndex.io.

What To Do in the Garden in September

As you’ve done all summer, continue to keep your plants hydrated, pull weeds, and watch for pests.

Here’s a snapshot of the activities you can do this month and those you should not be doing.

✅	Water deeply
✅	Watch for heat stress
✅	Watch for pests
✅	Fertilize lemons & limes
✅	Prune storm damage
✅	Prune perennials
✅	Harvest prickly pear fruit
✅	Plan for October
❌	Don’t plant most plants
❌	Don’t prune most plants
❌	Don’t fertilize most plants

Read on for all the details and exceptions!

Should You Plant in September? The Case for Waiting

Many gardening references state that September is a good time to plant trees, shrubs, perennials, and winter annuals.

But I disagree.

Many of these recommendations were written years ago, and things have changed. The past few Septembers have been brutally hot. Last September (2024), here in Tucson we had 16 days over 100. October, with 13 days over 100, brought little relief. That’s two months of heat stress for new plants.

So wait until mid-October or even November to plant. Your plants will experience less transplant shock and you’ll experience less stress.

You can plant cactus, agave, yuccas, and other landscape succulents this month, but if you can wait until spring, April is considered “prime time” for planting succulents.

If you get the overwhelming urge to plant or have a plant that needs to go in the ground ASAP, you can, but you’ll need to be extra vigilant about watering and protecting it from the sun. After a long, hot summer I’m burned out trying to water and protect.

Provide New Plants with Shade

If you do plant anything new this month, provide it with temporary shade.

Additionally, if you lost a tree or a large part of a tree due to storm damage, you may have plants that have suddenly lost their shade. This abrupt change can fry them.

You can provide temporary shade with shade cloth or something as simple as a patio chair. If you have fallen branches, you can use them to temporarily shade new plants. Patio umbrellas work great but don’t leave them up unattended. Sudden winds can knock them over or turn them inside out.

Also, be mindful that the position of the sun is changing. Relocate potted plants to account for the movement of the sun.

Watering

September generally gets less rain than the previous months and continues to be hot, so continue to water on a summer watering schedule.

Not sure how to water your plants in September?
These articles can help:
7 Tips for Watering Landscape Cactus
How to Water Desert Trees: How Often? How Much?
How to Water Desert Shrubs: How Often? How Much?

Fertilize Lemons & Limes

Citrus should be fertilized three times per year. If you didn’t fertilize your lemons or limes in August, fertilize them early in September. This will be their third (and final) application for the year.

(Other citrus — oranges, tangerines, grapefruit — should not be fertilized now. They should have had their final application in the spring.)

Fertilizing instructions can be complicated. How much fertilizer to use depends on the size of your tree and the amount of nitrogen (N) in your fertilizer. To determine exactly how much fertilizer your trees need, use the University of Arizona’s online Citrus Fertilizer Calculator.

Pruning Tasks

There are a few pruning tasks you can do this month.

You can deadhead spent blooms anytime and prune back leggy perennials, ideally once the temperatures stay below 100.

You can remove the 5 Ds — dead, diseased, deranged, damaged, or dangerous branches — from shrubs or trees.

If you have any large cactus or trees that were uprooted by storm damage or are leaning precariously, call a cactus specialist or an arborist. They might be able to reposition and save your plant.

Common Garden Pests in September

It’s a peak month for caterpillar migrations. Try co-existing with caterpillars, since they turn into beautiful and necessary moths and butterflies.

If you see something that looks like bird poop on your citrus, leave it alone. It’s the larval stage of the beautiful giant swallowtail butterfly and won’t hurt your tree.

Whiteflies and spider mites thrive in hot, dry weather. If you see them on your plants, give them a spray with the jet setting of your hose nozzle. If that doesn’t work, use insecticidal soap, but only when the temperature is below 90. Using soap in the heat can burn your plants’ leaves.

Harvest Prickly Pear Fruit

August through September is time to harvest ripe prickly pear fruit. Harvesting and preparing this fruit is definitely a process, so I’m going to direct you to the experts — Arizona-Sonora Desert Museum. Their article “Prickly Pear Harvesting 101” will tell you everything you need to know, including:

• What tools you’ll need
• Where you can legally harvest fruit
• How to select the best fruit
• How to process and juice the fruit
• Drink recipes

Plan, Don’t Plant

This month is the perfect time to plan (not plant!) what you want to plant later this fall. It’s important that you do a “post-mortem” of your garden at the summer so that you don’t repeat the same mistakes.

October is the best overall month for buying and planting landscape plants. November is a great time to plant, too, but nursery stock can run low.

• Are there any plants that didn’t make it and need to be replaced?
• Are there any plants that caused you more stress than happiness? Maybe it’s time to take them out and replace with plants better suited to their environment.
• Are there any bare spots in your yard beckoning for a new plant?

Before deciding on any new plant, make sure it’s a good choice for the spot you have in mind. Choosing the right plant can save you time, money, and disappointment. Here are the top 9 factors to consider before making any major purchases.

And you can find comprehensive plant profiles for over 140 popular landscape plants in our Desert Plant Library. This information is invaluable for finding the perfect plant for any spot.

Gardening Events in September

Tucson always has a lively gardening scene, and this month you can look forward to a growing number of gardening-related activities since some nurseries and organizations pause events during the summer.

Most weeks there are multiple garden-related events — classes, workshops, plant sales, musical events, food trucks, garden-related crafts, and more. There’s always a mix of both indoor and outdoor activities.

If you’re in the market for a new shade tree and don’t mind starting small, check out Tucson’s Trees for You Program which starts this month. Tucson Electric Power (TEP) customers can order two 5-gallon trees for $5 each.

Don’t live in Tucson? Look for classes being held online. You can participate in these no matter where you live.

You’ll find an up-to-date list of gardening-related activities in our Tucson Gardening Events Calendar.

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Photo Credits

Las Vegas Review Journal