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August

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August in the Low Desert

watering | what to plant | pruning | fertilization | problems


August in Arizona is the time when we all begin to wonder when the summer will end. Unfortunately, we have about two months left to endure. Monsoons clouds are beginning to build, the humidity is soaring and a few raindrops are falling.

This month you will notice that your succulent plants are succumbing to high nighttime temperatures. When the night temperatures stay at 90º F or above and the humidity is high, most succulent plants can’t breathe. After several nights in a row, chances are many of them will rot. Other than careful watering, there is nothing that can be done.

Watch the rain activity around your landscape. Note the runoff direction, where the puddles form, and areas of erosion. Why? This will help you re-contour your yard for more efficient water harvesting.

Keep note of the sun’s position in the sky. As the month progresses and the angle changes, you may begin to notice side-burning on plants, particularly cacti and succulents. Add small pieces of shade cloth until the days cool off.

Check your tree stakes and readjust if necessary. Remember staking should only be a temporary solution used to prevent the tree from falling over until it has established its root system. Tree staking should be done only when needed and stakes should be promptly removed after one or two growing seasons.

With the warm, abundant rainfall, look for summer annual wildflowers blooming such as Arizona Poppy (Kallstroemia grandiflora), Chinchweed (Pectis papposa), Golden Crownbeard (Verbesina encelioides), and Devil’s Claw (Proboscidea parviflora). These annuals will continue to bloom throughout the month and into late September.

The Desert Hackberry (Celtis pallida) will be full of fruit. Leave them for the birds and other wildlife. Same with the Prickly-pear cacti (Opuntia sp.), Organ Pipe (Stenocereus thurberi), and Senita (Pachycereus schottii)– let the fruits ripen and be eaten.

By mid-August begin to prepare a new vegetable garden bed for fall-winter planting. Prepare your vegetable bed by using a digging fork or rototilling to approximately 12-18 inches deep. Do not work soil if it is too wet as it can permanently damage the soil structure. Apply compost generously (several inches) and incorporate it into the loosened soil. If you have an existing vegetable garden this is also a good time to add compost and lightly work it into the soil.

With proper plant selection, you can provide your garden with color as there are many native and desert-adapted plants that will continue to flower through the summer and into the fall.

Blooming herbaceous perennials, groundcovers, bulbs, and vines can include:
•  Butterfly Mist (Ageratum corymbosum)
•  Bloodflower (Asclepias curassavica)
•  Desert Marigold (Baileya multiradiata)
•  Chocolate Flower (Berlandiera lyrata)
•  Wine Cups (Callirhoe involucrata)
•  Blue Mist (Caryopteris x clandonensis 'Dark Knight')
•  Damianita (Chrysactinia mexicana)
•  Mist Flower (Conoclinium dissectum)
•  Sacred Datura (Datura wrightii )
•  Desert Foldwing (Dicliptera resupinata)
•  Hummingbird Trumpet (Epilobium canum ssp. latifolium
•  Arizona Blue-eyes (Evolvulus arizonicus)
•  Texas Indian Blanket (Gaillardia pulchella)
•  Baja Bush Snapdragon (Galvezia juncea)
•  Gaura (Gaura lindheimeri)
•  Rock Verbena (Glandularia pulchella)
•  Arizona Rosemallow (Hibiscus biseptus)
•  Desert Rosemallow (Hibiscus coulteri)
•  Trailing Lantana (Lantana montevidensis)
•  Blackfoot Daisy (Melampodium leucanthum)
•  Showy Menodora (Menodora longiflora)
•  Rough Menodora (Menodora scabra)
•  Marvel of Peru (Mirabilis jalapa)
•  Desert Four O’Clock (Mirabilis multiflora)
•  Rock Penstemon (Penstemon baccharifolius )
•  Desert Plumbago (Plumbago scandens)
•  Paperflower (Psilostrophe cooperi
•  Mexican Evening Primrose (Oenothera speciosa)
•  Mexican Hat (Ratibida columnifera)
•  Baja Bush Snapdragon (Galvezia juncea)
•  Katie Ruellia (Ruellia brittoniana ‘Katie’)
•  Red Sage (Salvia coccinea)
•  Pink Sage (Salvia coccinea ‘Brenthurst’)
•  Desert Senna (Senna covesii)
•  Yellow Dots (Galvezia juncea)
•  Gaura (Gaura lindheimeri)
•  Rock Verbena (Sphagneticola trilobata)
•  Texas Betony (Stachys coccinea)
•  White Woolly Twintip (Stemodia durantifolia)
•  Dyssodia (Thymophylla pentachaeta)
•  Rain lilies (Zephyranthes spp.)
•  Desert Zinnia (Zinnia acerosa)
Blooming vines can include:

•  Queen’s Wreath (Antigonon leptopus)
•  Crossvine (Bignonia capreolata ‘Tangerine Beauty’)
•  Yellow Orchid-vine (Callaeum macropterum)
•  Arizona Grape Ivy (Cissus trifoliata)
•  Lavender Trumpet Vine (Clytostoma callistegioides)
•  Pringle’s Clustervine (Jacquemontia pringlei)
•  Slender Janusia (Janusia gracilis)
•  Purple Bushbean (Macroptilium atropurpureum)
•  Yellow Morning Glory-vine, Yuca (Merremia aurea)
•  Wait a Minute Vine (Merremia dissecta)
•  Passionflowers (Passiflora spp.) Blooming shrubs can include:
•  Prairie Acacia (Acaciella angustissima syn. Acacia angustissima)
•  Bee Brush (Aloysia gratissima)
•  Chihuahuan Honeysuckle (Anisacanthus puberulus)
•  Flame Anisacanthus (Anisacanthus quadrifidus var. wrightii)
•  Bougainvillea (Bougainvillea sp.)
•  Woolly Butterfly Bush (Buddleja marrubiifolia)
•  Red Bird of Paradise (Caesalpinia pulcherrima)
•  Baja Fairy Duster (Calliandra californica)
•  Little-leaf Cordia (Cordia parvifolia)
•  Indigo Bush (Dalea bicolor var. argyrea)
•  Sky Flower (Duranta erecta
•  Blue Emu Bush (Eremophila hygrophana)
•  Emu Bush (Eremophila laanii ‘Pink Beauty’)

•  Tree Ocotillo (Fouquieria macdougalii)
•  Ocotillo (Fouquieria splendens)
•  San Marcos Hibiscus (Gossypium harknessii)
•  Desert Cotton (Gossypium thurberi)
•  Guayacán (Guaiacum coulteri)
•  Mexican-honeysuckle (Justicia spicigera)
•  Lantana (Lantana camara)
•  Texas Sage (Leucophyllum frutescens)
•  Heavenly Cloud Texas Ranger (Leucophyllum x ‘Heavenly Cloud’)
•  Rio Bravo Texas Ranger (Leucophyllum langmaniae ‘Rio Bravo’™)
•  Cimarron Texas Ranger (Leucophyllum zygophyllum ‘Cimarron’®)
•  Mexican-oregano (Lippia graveolens)
•  Turk’s Cap (Malvaviscus arboreus var. drummondii)
•  Velvet-pod Mimosa (Mimosa dysocarpa
•  Desert Ruellia (Ruellia peninsularis)
•  Coral Fountain (Russelia equisetiformis)
•  Mexican Bush Sage (Salvia leucantha)
•  Velvet-leaf Senna (Senna lindheimeriana)
•  Silver Nightshade (Solanum hindsianum)
•  Yellow Bells (Tecoma spp.)
•  Skeletonleaf Goldeneye (Viguiera stenoloba)
Blooming trees can include:
•  Sweet Almond Verbena (Aloysia virgata)
•  Desert Willow (Chilopsis linearis)
•  Texas-olive (Cordia boissieri)
•  Texas Ebony (Ebenopsis ebano)
•  Kidneywood (Eysenhardtia orthocarpa)
•  Golden Leadball Tree (Leucaena retusa)
•  Screwbean Mesquite (Prosopis pubescens)

Blooming cacti and succulents can include:

•  Karoo Roses (Adenium spp.)
•  Elephant Tree (Bursera microphylla)
•  Big Needle Cactus (Coryphantha macromeris)
•  Golden-chested Beehive Cactus (Coryphantha recurvata)
•  Chain Fruit Cholla (Cylindropuntia fulgida)
•  Diamond Cholla (Cylindropuntia ramosissima)
•  Easter Lilies (Echinopsis spp.)
•  Red Torch (Echinopsis huascha)
•  Coville’s Barrel (Ferocactus emoryi)
•  Compass Barrel (Ferocactus cylindraceus)
•  Fishhook Barrel (Ferocactus wislizeni
•  Turk’s Head (Ferocactus hamatacanthus)
•  Midnight Lady (Harrisia pomanensis)

•  Giant Hesperaloe (Hesperaloe funifera)
•  Red Yucca (Hesperaloe parviflora)
•  Yellow Yucca (Hesperaloe parviflora ‘Yellow’)
•  Graham’s Pincushion (Mammillaria grahamii)
•  Artichoke Cactus (Obregonia denegrii)
•  Madagascar Palm (Pachypodium lamerei)
•  Slipper Plant (Pedilanthus macrocarpus)
•  Queen of the Night (Peniocereus greggii)
•  Rose Cactus (Pereskia aculeata)
•  Guyapa (Pereskia sacharosa)
•  Octopus Cactus (Stenocereus alamosensis)
•  Bird’s Nest Cactus (Thelocactus rinconensis)
•  Turbinicarpus viereckii ssp. neglectus

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Watering

Proper irrigation to your plants during the summer months is crucial. As the temperatures rise, plant watering needs will also increase. Continue to water your established and newly planted landscape plants according to the summer schedule (See July’s calendar). However, adjust your watering schedule if your garden receives a deep, substantial rain event. 

Monsoons bring humidity and moisture to the low desert. More and more we see periods of high night temperatures of 90º F and above during this time.  This makes it a risky month for watering cacti and some other succulents, particularly aloes. It is imperative to allow the soil to dry out for at least a week or two to prevent your cacti and succulent plants from rotting. Be sure to adjust your irrigation timers if we receive a good soaking rain. 

Mediterranean plants and California chaparral plants, such as Cleveland Sage (Salvia clevelandii) and White Sage (Salvia apiana) can be easy to overwater during this time. Allow the soil to dry out between watering. If these plants are on the drip system, consider using an emitter that can be shut off during this time.

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What to Plant

When planting native and desert-adapted plants, it is usually unnecessary to back-fill with soil amendments and vitamins or to add rooting hormones. Take a look at our Desert Gardening Guide on How to Plant Desert-Adapted Trees and Shrubs.

Although fall is the better time, with the higher humidity we can get away with planting trees and warm-season shrubs and vines now but not herbaceous perennials. It is imperative, when planting during the summer months, to monitor your plantings carefully for signs of water stress particularly if it has been drier than usual.

Always water your trees and shrubs immediately after planting and monitor the moisture for the next few days to keep the root ball from drying out. Gradually extend the time between watering.

Trees to be planted include:
•  Anacacho Orchid-tree (Bauhinia lunarioides)
•  Desert Willow (Chilopsis linearis)
•  Texas-olive (Cordia boissieri)
•  Texas Ebony (Ebenopsis ebano)
•  Kidneywood (Eysenhardtia orthocarpa)
•  Palo Brasil (Haematoxylon brasiletto)
•  Mexican Ebony (Havardia mexicana)  
•  Golden Leadball Tree (Leucaena retusa)
•  Desert Fern (Lysiloma watsonii)

•  Palo Blanco (Mariosousa willardiana syn. Acacia willardiana)
•  Ironwood Tree (Olneya tesota)
•  Palo Verdes (Parkinsonia spp.)
•  Mesquites (Prosopis spp.)
•  Catclaw Acacia (Senegalia greggii syn. Acacia greggii)
Shrubs to be planted include:
•  Bee Brush (Aloysia gratissima)
•  Baja Fairy Duster (Calliandra californica)
•  Red Bird of Paradise (Caesalpinia pulcherrima)
•  Little-leaf Cordia (Cordia parvifolia)
•  Skyflower (Duranta erecta)
•  Mexican Tree Ocotillo (Fouquieria macdougalii)
•  Desert Cotton (Gossypium thurberi)
•  Guayacán (Guaiacum angustifolium)
•  Guayacán (Guaiacum coulteri)
•  Fire Bush (Hamelia patens)
•  Malabar-nut (Justicia adhatoda)
•  Lagascea (Lagascea decipiens)
•  Lantana (Lantana camara)
•  Texas Rangers (Leucophyllum spp.)
•  Velvet-pod Mimosa (Mimosa dysocarpa)
•  Slim-pod Senna (Senna hirsuta var. glaberrima)
•  Yellow Bells (Tecoma spp.)

Herbaceous perennials and groundcovers should be planted in fall or spring. However, many warm-season vines can be planted during the summer months. Water immediately after planting and monitor the moisture for the next few days to keep the root ball from drying out. Water newly planted native and desert-adapted vines twice to three times weekly to a depth of at least a foot. Gradually extend the time between watering and monitor plants regularly for signs of water stress.

Vines to be planted include:
•  Queen’s Wreath (Antigonon leptopus)
•  Yellow Orchid-vine (Callaeum macropterum
•  Old Man’s Beard (Clematis drummondii)
•  Arizona Grape-ivy (Cissus trifoliata)
•  Slender Janusia (Janusia gracilis
•  Purple Bushbean (Macroptilium atropurpureum)
•  Yellow Morning Glory-vine, Yuca (Merremia aurea)
•  Passionflowers (Passiflora spp.)
•   Arizona Canyon Grape (Vitis arizonica)

Many cacti and warm-season succulents can still be planted in the summer. When transplanting cacti and succulents, mark either the south or west side and plant facing the orientation you marked to avoid the burning of tender tissues. Most nurseries will mark the side of the container to help you determine proper planting orientation. However, if the original orientation is not known, newly planted cacti and succulents need to be covered with shade cloth if the plant surface appears to yellow or pale suddenly. Use a shade cloth rated between 30-60% as anything higher will block most of the sunlight and will not be suitable for your cacti and succulents. You may need to keep the shade cloth on the plant for the duration of the summer to prevent sunburn. After planting your cacti and succulents wait about a week before watering to minimize the chance of rot.

Plant cacti and warm-season succulents including:
•  Agaves (Agave spp.)
•  Ponytail Palm (Beaucarnea recurvata
•  Burseras, Elephant Trees (Bursera spp.)
•  Chollas (Cylindropuntia spp.)
•  Golden Barrel (Echinocactus grusonii)
•  Horse Crippler (Echinocactus texensis)
•  Hedgehogs (Echinocereus spp.)
•  Easter Lilies (Echinopsis spp.)
•  Candelilla (Euphorbia antisyphilitica)
•  Pencil Tree (Euphorbia tirucalli)
•  Barrel cacti (Ferocactus spp.)
•  Midnight Lady (Harrisia sp.)
•  Giant Hesperaloe (Hesperaloe funifera)
•  Red-yucca (Hesperaloe parviflora)
•  Pincushions (Mammillaria spp.)
•  Prickly-pears (Opuntia spp.)
•  Old Man of the Andes (Oreocereus celsianus)
•  Mexican Fence Post (Pachycereus marginatus)
•  Senita (Pachycereus schottii)
•  Slipper Plant (Pedilanthus macrocarpus)
•  Queen of the Night (Peniocereus greggii)
•  Elephant Food (Portulacaria afra)
•  Organ Pipe (Stenocereus thurberi)

 

Cacti seed can still be continued to be planted.   Seed can be soaked overnight in water to help begin the germination process.  Place seed in a well-draining soil mix (½ quality potting soil and ½ perlite or pumice) and lightly cover.  Keep soil moist until germination occurs.  See our Desert Gardening Guide on Growing Cacti from Seed. 

Herb seeds to sow include:
•    Blackeye peas
•    lima bean
•    summer squash
•    carrots
•    corn 
•    green onion

•    green snap bean
•    carrots
•    Hopi red-dye amaranth
•    oregano
•    parsley
•    tepary beans
•    beans
Try the many varieties of corn and beans from Native Seeds/search.
Vegetable seeds to sow in late August include:
•  brussel sprouts
•  cauliflower
•  collards
•  kale
•  lettuce, head and leaf
•  broccoli
•  cabbage
•  rue
•  celery
•  cucumbers
•  leeks
•  kholrabi
•  mustard

If your tomatoes made it through the summer, cut them back; tomato transplants can now be planted if they can be provided some shade for a fall harvest.

Cabbage, broccoli and cauliflower can all be started indoors from seed for fall planting. 

Wait until fall or spring to plant most herbs.

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Pruning

Pruning should be done to maintain plant health (remove dead, damaged or diseased portions, cross branching, etc.), to highlight the “natural” shape of the plant, to train a young plant, and to eliminate hazards. Excessive or heavy pruning causes significant stress to trees and shrubs. The best practices are to prune the least amount necessary and prune for legitimate reasons. How much to prune depends on the size, species, age, as well as your intentions. Two good principles to remember--a tree or shrub can recover from several small pruning wounds faster than from a single large wound and never remove more than 25% of the canopy in a year. 

The extra humidity will elicit new growth on trees and shrubs. Minimal pruning should be performed during this month. Remove dead or broken branches and repair storm damaged areas but do not open up the canopy just yet.

Pruning newly planted trees is not recommended and in fact, can be detrimental. However, at planting time prune broken or torn and diseased branches. Save other pruning actions for the second or third year.  For more information on developing a healthy tree visit www.treesaregood.org

Prune your cacti if necessary to maintain size, for propagation or to remove a damaged or diseased stem; prune at joint or segment.  Use a sharp, clean pruning tool and spray tool periodically with a 70% alcohol solution to prevent infection.  If the pruned stem is to be used for propagation, allow the cutting to dry out for a week before planting. Check out our Desert Gardening Guide on Rooting a Cactus Cutting for more information.

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Fertilization

We do not recommend fertilizing your desert-adapted landscape plants during the summer months.  Fertilizing will cause excessive, luxuriant growth that requires more water and new growth is too tender to take the excessive heat and sun exposure.  Wait until next spring to fertilize, if needed.

Periodic fertilizing may be needed for plants in containers as nutrients in the soil will have diminished over time.  Always follow directions on the label.    

Continue to fertilize your warm-season annuals and herbaceous and woody perennials in containers if necessary.   

Cacti and warm-season succulents in containers should be fertilized at least once during the month depending on the type of fertilizer used. Do not fertilize any winter-growing succulents such as Succulent Geraniums (Pelargonium spp.), Iceplants (Malephora spp., Drosanthemum spp., Cephalophyllum spp.), Living Stones (Lithops spp.) and crassulaceous plants (Kalanchoe spp., Cotyledon spp., Echeveria spp., Dudleya spp.) as they are summer dormant.

Continue to water and fertilize your Karoo Roses (Adenium spp.) to promote bloom through the warm season. Check out our video on how to care and maintain your Karoo Roses or download our Desert Gardening Guide.

Continue to fertilize your vegetable and herb garden as needed.  

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Problems

This month you’ll see an abundance of insect activity. Mosquitoes are now commonplace throughout the Valley. Be sure to empty any containers, buckets, bowls, etc. that might catch rainwater as the larvae require water in which to mature. 

Cicadas are still buzzing away at this time and stem damage may be evident from their egg-laying. See July’s calendar for more information.

Ants and termites are swarming and if you see the mud tunnels of termites crawling up your plant stems, just wash them off. They are not harming the plants. 

If you notice your agave collapsing or its leaves drooping, it may be infested with the Agave Snout Weevil. For detailed information on the life cycle, symptoms, prevention and treatment go to our Agave Snout Weevil Desert Gardening Guide.

Defoliation of many landscape plants can occur with the appearance of a high infestation of grasshoppers. Population size varies year to year and they are a difficult insect to manage in the garden. When population numbers are low, hand-pick and remove. If infestation is high, use a protective cloth or floating row cover to protect your plants.  

Powdery mildew may also be showing up on your perennials such as penstemons and vegetable plants.  There are many species of this fungus and symptoms appear on leaf and stem surfaces as white spots. For more information go to http://ag.arizona.edu/pubs/diseases/az1124/#pm on how to prevent and treat powdery mildew.

Aphids will show their presence.  The excrement or “honeydew” from aphids may cause sooty mold to appear, especially on the Desert Milkweed (Asclepias subulata) and Penstemons (Penstemon spp.). Sooty mold does not infect plants but will grow where “honeydew” has accumulated. If sooty mold is permitted to spread over the surface of the plant, it can prevent light penetration and limit the plant’s ability to photosynthesize. To discourage aphids spray them off with water or use an insecticidal soap or horticultural oil. Wipe leaf surfaces off with soap and water to remove sooty mold. 

Palo Verde root borers are active and they’ll emerge around your trees’ drip lines but, there isn’t much that can be done about them. See July’s Gardening Calendar for more information on Palo Verde Root Borers.

Whiteflies are small, sucking insects that are often found on many ornamental and vegetable plants. Plants infested with whiteflies show symptoms of sticky, yellowing leaves and when the plant is disturbed the small insects will fly generating a white “blur”.  There are many species of whiteflies and they are abundant at different times of the year.  Whiteflies are difficult to control and insecticides are not recommended as it can disturb and destroy their natural enemies. If you choose to use an insecticide, use an insecticidal soap or oil to help manage populations.

Large, green caterpillars may be appearing on tomatoes, eggplant and even the Sacred Datura (Datura wrightii).  They can either be the tobacco or tomato hornworm feeding on the leaves, flowers and stems. After three to four weeks of feeding, the larva will burrow into the soil to pupate.  In approximately two months, the large adult moth will appear and are often mistakenly identified as hummingbirds.  These moths are important pollinators for many nighttime flowering plants including the Sacred Datura (Datura wrightii), Fragrant Evening Primrose (Oenothera caespitosa), and the Queen of the Night (Peniocereus greggii). No method to control is necessary. If infestation is high, hand-pick caterpillars off your plants or allow naturally occurring parasites to help control the population.

A white, cottony mass may appear on ornamental and edible plants and is sometimes confused with cochineal scale because they too produce a waxy, white cottony substance. Both insects feed on plant juices, however, cochineal scale feed exclusively on cacti such as Prickly-pears (Opuntia spp.) and Chollas (Cylindropuntia spp.). Mealy bugs are often difficult to control and systemic insecticides may be used, but may not always be effective. However, usually dipping a cotton swab with a 50-50 mixture of rubbing alcohol and water solution and then wiping on these insects can help manage the population. Mealy bugs are also a common problem for many cacti and succulents grown indoors or in greenhouses and are often found either on the leaves, stems or roots. Take the infested plant(s) outdoors during the summertime as this seems to help get rid of these pests. It takes constant vigilance to keep them under control.

Cochineal scale, that cottony substance all over your prickly-pears may also be active now. Wash them off with a hard spray of water or use insecticidal soap. 

Many butterfly species are in abundance this month, particularly the Gulf Fritillary. You’ll see the Gulf Fritillary larvae or caterpillar on Passionflowers (Passiflora spp.) but, unless the damage is significant, leave them to become the next generation of butterflies.

Would you like to remove your Bermuda grass lawn?  The hot summer months are the best times to begin treatment for eradicating Bermuda grass.  For more information check out our Desert Gardening Guide on Bermuda Grass Removal.

For more information on diseases or problems of landscape plants go to the University of Arizona Cooperative Extension publication http://ag.arizona.edu/pubs/diseases/az1124.pdf or the University of California UC IPM Online at http://www.ipm.ucdavis.edu/PMG/menu.homegarden.html

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