nurse plants

 Young saguaro cactus were peeking out from its bursage nurse plant.

As you walk through the desert, there are many opportunities to view some of the striking cacti and their unique shapes.  What is not initially apparent, are the many examples of plants helping young cacti survive.  However, if you look closely, it is all around you – desert shrubs and trees sheltering growing cacti from the harsh desert climate. 

nurse plants

 Young barrel cactus underneath a bursage nurse plant

Despite their tough, prickly appearance, cactus are quite vulnerable.  Of the thousands of seeds that are released by each cactus, only a tiny fraction grow into new cactus plants.  Most would not survive if it were not for “nurse plants.”   These plants provide much-needed protection from the sun, cold temperatures and predators (including humans).  Nurse plants also provide much needed additional moisture for the new cacti.

nurse plants

 Mammillaria microcarpa 

It is easy to walk by and not even notice the presence of the small cacti growing underneath nurse plants.  Most of the year, the fishhook cactus (Mammillaria microcarpa), pictured above, are almost impossible to see.  It is only in the spring when they are blooming that you can spot them.

nurse plants

 Hedgehog cactus outgrowing it’s bursage nurse plant.

For the smaller cacti species, bursage (Ambrosia deltoidea) most often serves as the nurse plant.  It also often serves as the first nurse plant for saguaro cacti.

Two young saguaro cacti

 Two young saguaro cacti outgrowing their creosote and bursage nurse plants

Creosote (Larrea tridentata), palo verde, mesquite or ironwood trees often serve as the nurse plants for larger species of cacti.  As it grows larger, it requires more water and nutrients from the soil, which leaves little for the nurse plant.  So frequently, the nurse plant will decline and die as you can see from the photo above.

Young buckhorn cholla emerging from its bursage nurse plant

 Young buckhorn cholla emerging from its bursage nurse plant.

So next time you have the opportunity to take a walk in the desert, look around….you will most likely see examples of this unique relationship of plants helping young cactus survive.

Drought Tolerant and Beautiful: Globe Mallow

Iconic tree

  Iconic tree, Blue Palo Verde (Parkinsonia florida)

When people think of the Sonoran desert, hillsides studded with saguaro cactus and cholla often come to mind.   But interspersed between the cactus, you will find the iconic palo verde trees with their beautiful green trunks and branches.

The word “Palo Verde” means “green stick” in Spanish, referring to their green trunk, which is a survival mechanism in response to drought.  

Palo verde trees are “drought deciduous,” which means that they will drop their leaves in response to a drought situation.  Their green trunks and branches can carry on photosynthesis, even in the absence of leaves. 

'Desert Museum' Palo Verde

 ‘Desert Museum’ Palo Verde (Parkinsonia hybrid ‘Desert Museum’)

Palo verde trees act as a “nurse plant” to young saguaro cacti by protecting them from the cold in the winter and from the intense sun in the summer.  Beautiful, yellow flowers are the product in the spring.    

Desert Museum' Flower

 Desert Museum’ Flower

There are three species of palo verde that are native to the desert Southwest; blue palo verde (Parkinsonia florida), formerly (Cercidium floridum), foothill palo verde (Parkinsonia microphylla), formerly (Cercidium microphyllum) and ‘desert museum’ palo verde (Parkinsonia x ‘Desert Museum’)

Another species of palo verde that is prevalent in the landscape are called palo brea (Parkinsonia praecox), formerly (Cercidium praecox).  They have a dusty green trunk and branches that twist and turn.  Their cold hardiness range is around 15 to 20 degrees F.

Iconic tree

 Iconic tree, Palo Brea

PALO VERDE USES: Palo verde trees serve as beautiful specimen trees where their green trunks, branch structure, and flowers serve as an attractive focal point in the landscape.  They are drought tolerant, once established and provide lovely filtered shade year-round.  

When deciding where to place your tree, be sure to take into account that they need a lot of room to grow, mature sizes are listed below.  

Palo Verdes don’t do well when planted in grass and will decline over time.  Locate away from swimming pools due to flower litter in the spring.

Because of their more massive thorns and branching tendency to point downwards, palo brea trees aren’t recommended in areas close to foot traffic.  

Mature Sizes:

Blue Palo Verde – 30 ft x 30 ft

‘Desert Museum’ Palo Verde – 30 ft high x 40 ft wide

Palo Brea – 30 ft x 25 ft

Foothills Palo Verde – 20 ft x 20 ft

As with many desert trees, Palo Verde trees have thorns, except for the ‘Desert Museum’ Palo Verde.  

Iconic tree

 Foothills Palo Verde

PALO VERDE MAINTENANCE:  Prune to elevate the canopy and maintain good structure.  Avoid hedging and “topping” trees as this stimulates excess, weak growth.

MY FAVORITE: As a landscape manager, horticulturist and arborist, I have grown and maintained all of the palo verde species mentioned, and I truly enjoy them all.  However, at home, I have 4 ‘Desert Museum’ trees.  In comparison to the other species, their trunks are a deeper green; they produce larger flowers, are thornless and grow very quickly in the desert.  Also, they require little, if any, tree staking when planted. 

Fall Rose, 'Double Delight'

 Fall Rose, ‘Double Delight’

In the Desert Southwest, we are blessed with two different blooming seasons – spring and again in fall.  

While two bloom seasons is generally one more than many regions experience, roses don’t enjoy the heat of summer and go into summer dormancy.  That means that they just exist and don’t grow or bloom significantly. Their leaves may show signs of sunburn.

Fall Rose, 'Medallion'

 Fall Rose, ‘Medallion’

However, once September arrives and the days begin to grow shorter and temperatures begin to cool, it is time to lightly prune your rose bushes, which will stimulate new growth. 

Begin by pruning back 1/4 of the top growth, removing sunburned foliage and any flowers present.  

As always, prune back to an outward facing bud at an angle of 45 degrees.  Seal any pruning cuts larger than the diameter of a pencil with Elmer’s glue to prevent borers.

Fall is also time to fertilize roses in preparation for their fall bloom season.  Apply an organic fertilizer formulated for roses.  Afterward, be sure to water in well.

'Abraham Darby'

 ‘Abraham Darby’

**For those that want to go the extra step, I would recommend soil amendments such as compost and manure in addition to rose fertilizer, which results in greater growth, lush foliage and blooms over the long term.  

To do this, first make 4 – 5, six-inch deep holes around each rose, placing them at least 1 ft. from the center (I use the end of a broom handle for this).  Then apply a mixture of aged steer manure and alfalfa pellets (rabbit food) and pour into each hole.  Water in well.  

The aged manure improves the soil structure and slowly releases nutrients.  The alfalfa pellets release a type of alcohol as they break down that roses just love.

By lightly pruning and fertilizing in early fall, you’ll enjoy a fall filled with beautiful roses.

Saguaro cactus

In the past, people have asked me how long does a saguaro cactus arm take to grow back. The commonly held belief is that it takes 100 years before they will develop an arm.

However, as with much plant information, this answer is not always correct, it actually takes less time for a saguaro cactus to grow its arm back in a landscape setting than it’s native habitat.  

The most critical factor in determining the timing of when a saguaro will start to grow an arm is the availability of water. Put simply, the more water a saguaro receives, the more quickly it grows. In a landscape setting where irrigation is present, a saguaro will grow much more rapidly then they do in their natural desert habitat. Saguaro cacti that grow in southern Arizona (near Tucson) grow more quickly than those in the western areas of the Sonoran desert because there is more rainfall in southern Arizona. 

A saguaro growing in its native habitat can take 50 – 100 years to grow arms. In a landscape setting, arms often appear much earlier.