Every Tucson Home Needs A Creosote Bush

Creosote-bush_Larrea_tridentata_flowersseeds.jpg

Creosote bush
Larrea tridentata
Zygophyllaceae

  •  Typically about 4-5' tall and wide but can get much larger

  • Responsible for "desert rain smell"

  • Tolerant of extreme heat, full sun

  • Low water user (top zone)

  • Blooms in warm weather

  • Hardy to about 15°F

  • Important species for native bees

Tucson has a particular smell, and that smell is caused by the creosote bush (Larrea tridentata). When the monsoon comes and the rains gush from the sky, the aroma that has ensnared every red-blooded Tucsonan (and many visitors) wafts along with the winds--phenolic compounds from creosote bush which have been carried by wind and moisture. 

As Tucson changes, and developers convert beautiful desert into monoculture housing developments and strip malls populated by Starbucks and Mattress Firm, we lose more and more of what makes this place so special. 

This summer we are launching a campaign to help keep Tucson smelling like Tucson.

We want every yard in Tucson to have at LEAST one creosote bush. 

Creosote bush is easy to grow. Once established it requires very little water (though some water will make plants look lusher and grow faster). Plants do best in full sun, and in hot locations where few other plants thrive. Give them lots of room to grow as they generally grow about 4-5 feet tall, though they have been known to get up to about 12 feet tall in special conditions. Surprisingly they take well to pruning, so you can keep them at bay if they seem to wanna sprawl out more than space allows. 

This plant is fascinating on many levels. In the wild, it grows where nothing else will, on hot dry, caliche ridden, barren soils. It is probably the most drought tolerant plant in North America. They photosynthesize only in the morning — which is why, if you start paying attention, you may notice that the foliage tends to face southeast, to take advantage of the morning sun. Resins on the leaves slow transpiration and plants can temporarily shed leaves and stems in extreme conditions. Creosote bush can also keep photosynthesizing when leaves are fairly decimated, keeping it alive in rough times.

The stems emerge from the base, and new stems form on the outside, which over a number of years begins to form a ring of clones. There is a famous colony, called the King Clone, in the Mojave Desert that is roughly estimated to be around 11,000 years old, one of the oldest-known organisms in the world.

 The 11,000 year old King Clone

The 11,000 year old King Clone

While creosote has a reputation for being fairly competitive, ecologically (some studies suggest plants secrete allelopathic chemicals that exclude other species from growing near them), from what I’ve witnessed, when there are solid stands of creosote bush, it is growing in soils that most other plants could not inhabit anyway. And that probably makes it an important pioneer plant — their structure encourages biomass to collect at their bases, enriching soils. Also, creosote bush is known as an important nurse plant (providing shade) to many succulent plants. Rodents love the soil beneath, and select these spots for their burrows, adding to the richness of the soil, and providing habitat for other organisms like lizards and insects when abandoned. This species is also very important to bees, especially in spring when bees really need the nectar and begin building up their colonies.

 That's not a stem! That's  Diapheromera covilleae

That's not a stem! That's Diapheromera covilleae

Numerous insects have evolved specifically with the creosote bush, including the creosote walking stick (Diapheromera covilleae) that mimics the creosote from birth to death, looking like new creosote leaves when young and when old, resembles the older, more mature twig growth. A scale insect, Mexican lac scale (Tachardiella larreae), feeds upon creosote bush and then exudes lac, a substance some people use as a sealant, or as glue.

Many larger creatures depend on the plant for shelter and a few as food. Black-tailed jackrabbits (Lepus californicus) are the only known mammal species to eat the plant's leaves, which have a bitter taste and are only eaten when they can find no other source of food. Desert woodrats (Neotoma lepida) and Merriam's kangaroo rats (Dipodomys merriami) depend greatly upon creosote bush seed. 

There are other non-mammals that eat creosote: chuckwallas eat creosote bush flowers, leaves, fruit. Specimens range in size depending on the conditions, averaging 3-6 feet tall. Plants in landscapes tend to get larger without pruning, up to 10 feet tall. If you plant a creosote bush in your yard, select the most punishing, hot, sunny spot you can find. Plants that don’t get full sun tend to be leggy. Once established, they take well to pruning. But the best-looking plants are the hard-grown plants in full sun. Flowers occur heavy in the spring, but are a response to any significant rainfall. They are followed by silvery, fuzzy, pea-sized fruits. The stems are conspicuously, and rather gorgeously, segmented.

 Midge gall on creosote bush

Midge gall on creosote bush

You might find an odd growth pattern on some plants caused by a midge fly (one of many Asphondylia species). The female midge inserts her egg along with a fungal spore from a mycangia (a small pocket to store fungal spores). A gall forms and the fungal mycelium grows to line the inside of the gall, when the egg hatches the developing larva feeds upon the fungus. Adult emergence is timed with periods of plant growth associated with winter, spring, or summer rain fall.

Katherine Gierlach