August: What to Do in the Desert Garden

August in the desert southwest is a lively month of contrasts as sporadic storms can bring welcome rain and cool fronts, and beautiful sunsets. But it can also bring pests, floods, and damaging winds. Here’s what tasks to do in the garden, problems to watch out for, and more during this changeable month.

August in the southwest is the heart of the monsoon. If you’ve had some rain, you may notice that wild areas, particularly the mountainsides, are greening up and summer’s “monsoon” wildflowers may even be in bloom.

Many desert dwellers find the monsoon storms and beautiful sunsets thrilling, but it’s not all roses for gardeners. Monsoon storms can bring flooding, hail, dust storms, and damaging wind. And an increase in moisture leads to an increase in insects and plant diseases.

Monsoon rains bring out more wildlife, some of which you may be delighted to see, and some, not so much. You’re likely to see more mammals, birds, snakes, toads, and insects of all kinds.

August Weather Outlook

August is a mixed bag weather-wise for both you and your plants. The good news is that the average temperature drops a few degrees from July. However, the humidity continues to rise slightly and the average rainfall drops by half an inch in Tucson, but only marginally in Phoenix.

Here’s a look at August weather averages in both Tucson and Phoenix:

August Weather Averages (Tucson)

High temperature	98°F
Low temperature	74°F
Precipitation	2.09″
Relative humidity	45%
UV index high	10.6
Wind	14 mph

August Weather Averages (Phoenix)

High temperature	105°F
Low temperature	83°F
Precipitation	1.00″
Relative humidity	32%
UV index high	9.7
Wind	7 mph

If you live elsewhere, enter your city or town in the search bar at TimeandDate.com to find your monthly averages.

What To Do in the Garden in August

August is a somewhat busier month in the garden than July. There are more plants to be pruned and fertilized, and more pests to watch out for, too.

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, weeds
✅	Fertilize citrus, palms
✅	Prune storm damage
✅	Prune perennials
❌	Don’t plant
❌	Don’t prune most plants
❌	Don’t fertilize most plants

Read on for all the details and exceptions!

Should You Plant in August?

Virtually all landscape plants will be much happier when planted in the fall, and it’ll be less work for you, too.

While some landscape plants can be planted now (i.e., cactus and other succulents, palms), I don’t recommend it. It’s better to plant these heat-lovers in the spring.

Start Planning

While August isn’t a good to to plant, it is a good time to plan what you want to plant in the fall. If you are considering a new tree and live in Tucson, you might want to check out the Trees for You Program.

Every fall TEP (Tucson Electric Power) customers have the opportunity to buy two 5-gallon trees for $5 each. The first day to order in 2025 is September 2.

Watering

Once the rains come, adjust your watering schedule. You can skip the next scheduled watering any time you receive .5 inches of rain or more.

I use a rain gauge to keep track of my rainfall. If you don’t have one, you can check out the rainfall map at the University of Arizona’s RainLog.org to see the rainfall totals nearest to you.

Not sure how to water your plants in August?
These articles can help:
How & Why to “Deep Water” Desert Plants
7 Tips for Watering Landscape Cactus
How to Water Desert Trees: How Often? How Much?
How to Water Desert Shrubs: How Often? How Much?

Now is a good time to harvest rainwater. It doesn’t need to be anything fancy – simply collect it in whatever you have around that will hold water.

I have a rain barrel connected to a downspout, but I still set 5-gallon buckets around my roofline — you can never have too much rainwater! Then I cover them with snap-on lids to keep out mosquitoes.

And now that the humidity is up, I collect AC condensate, an overlooked source of free “gray water.” I get anywhere from 2 to 5 gallons this time of year. Here’s my simple set up. (The lid with a hole is to keep out critters.)

If you experience a power outage, check your irrigation controller and reset it if needed.

If you are watering with a hose, always check the water temperature. Water from a hose can be hot enough to damage your plants.

What to Fertilize

While most plants should not be fertilized this month, there are a few exceptions.

Fertilize Citrus

Citrus should be fertilized three times per year. Lemons and limes should be fertilized at the end of August or the beginning of 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. It 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 handy online Citrus Fertilizer Calculator.

If your tree is one or two years old, there is no need to fertilize yet.

Watch for Iron Chlorosis

Iron deficiency sometimes shows up in the summer, especially in citrus and other non-native plants, and plants that have been overwatered. The telltale sign of iron chlorosis is yellow leaves with distinctly green veins.

If you have a plant showing signs of iron chlorosis, now is a good time to treat your plants. Learn how in this article: Why Desert Plants Get Iron Chlorosis (& what to do).

Fertilize Palms

I’m not keen on having to buy a different fertilizer for every type of plant, I think it’s a marketing ploy to get you to buy more stuff.

However, palms really do have unique needs and benefit from special palm fertilizer. August (along with May) are the ideal months to fertilize palm trees.

Fertilize Container Plants

Potted annuals, succulents, or any other plants you have growing in containers should be fertilized this month. Plants in pots have limited access to nutritional resources and can eventually use up all the nutrients in the potting soil.

Pruning Tasks

There are a few minor pruning tasks you can do in August. If you’re like me, you’re eager to tidy things up!

Native trees, especially palo verdes and mesquites can be pruned now with no problems. Heat-loving shrubs like oleander, red or yellow bird of paradise, or yellow bells can be lightly shaped.

Overgrown or leggy perennials and ground covers can be cut back by one-third to encourage new growth. Continue to deadhead spent flowers, especially those in containers, to encourage new blooms.

If You Have Storm Damage

Monsoon rains plus heavy winds are a recipe for storm damage. If your trees or shrubs have experienced minor storm damage, remove any damaged or dead branches.

For more substantial damage to large plants, there are two kinds of help.

If you just need broken branches or a fallen tree cut and hauled away, it’s not hard to find this kind of help. There are many “landscapers” that can do this for you.

However, if you have a tree that’s severely damaged, call an arborist. A certified arborist is your best shot at saving your tree and restoring it to its former health and beauty.

And if you have a large cactus that’s leaning precariously, call a cactus specialist. They might be able to prune or reposition your plant before it’s too late.

Got branches?
Tucson’s Reid Park Zoo takes them to feed their animals.
Learn more about this program here.

Common Garden Problems in August

Continue to monitor your plants for signs of heat and drought stress, particularly if you haven’t had much rain. If you are experiencing worse than normal heat, you can find heat wave survival tips here.

If you’ve lost a tree or a large part of a tree, you may have plants that have abruptly been exposed to full sun. This sudden change can fry your plants. Provide temporary shade however you can — with shade cloth or a patio umbrellas. You can even use your fallen branches to temporarily cover plants.

Garden Pests & Diseases

Continue to watch for insect infestations. Many insects are at their peak populations in August. Some common insect pests you may notice on your landscape plants this month include:

• ants
• aphids
• cochineal scale
• crickets
• spider mites
• white flies

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.

Check around your yard for standing water which could harbor mosquitos. Empty pots, saucers, or any other forgotten nooks that hold water after rains. If you can’t empty them, add bits of mosquito dunks.

If you have a plant that’s been defoliated over night, it could be the work of leafcutter ants. They bring leaves back to their nest, which they use to cultivate fungus as their food source. They have underground colonies that can go 8 feet deep and cover one acre! 😮

I find they usually go for one particular plant while bypassing others. As soon as I notice ant activity, I put a ring of Borax around the plant — they won’t cross it. Diatomaceous earth works, too.

If you have vincas (Catharanthus roseus) that wilt, but don’t recover from watering, pull them up and toss them. They are almost certainly infected by an untreatable, contagious soil fungus known as vinca wilt.

Weeds & Wildflowers

If the monsoon has brought you rain, you may find new weeds popping up in your yard. Try to pull them as soon as they appear since weeds are easiest to pull when the ground is saturated.

If you sowed monsoon wildflower seeds early in the summer, they should be coming up this month, so be careful not to pull seedlings while weeding.

Fun Gardening Events in August

If you live in Tucson, be sure to check out these ongoing evening events now through August. (You may have similar festivities near you.)

• Tohono Chul’s “Chillin’ at the Chul”
• Arizona-Sonora Desert Museum’s “Cool Summer Nights”
• Tucson Botanical Garden’s “$5 Fridays”

And of course, there are always garden-related classes, workshops, plant sales, musical events, food trucks, garden-related crafts, and more.

You’ll find a list of gardening-related events in our Tucson Gardening Events Calendar.

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