Why Do Cactus Have Spines ?

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spines of cactus

What comes to mind when you think of cactus?  

Perhaps the first thing you think of is the spines. If you have ever been unfortunate enough to have been pricked by a cactus, you’ll likely never forget that most of them have needles.  

*Did I ever tell you about the time I worked on golf course landscape and backed into a teddy bear cholla and got an entire piece lodged in the back of my leg?

Besides being painful to those who get too near to cacti, did you know that there are important reasons that cacti have spines?

spines of cactus

 Golden barrel cactuses (Echinocactus grusonii)

First, let’s look at the spines of cactus for what they are – the main part of cactus often functions as a modified stem, and its needles are the leaves.

The most obvious function of cactus spines is to protect the cacti from animals and people. There are, however, a few animals who aren’t deterred by the sharp spines of cacti such as javelina, tortoises and pack rats.

spines of cactus

 Saguaro cactus (Carnegiea gigantea) spines

Suprise, the primary function of the spines are to actually shade the cactus.

Although just one small spine would hardly provide shade, thousands of them can provide enough.

Why is sun protection needed for the surface of cacti? The shade from the spines let the cactus lose water through the atmosphere. This helps keep the cactus temperature relatively low.

spines of cactus

 Black-spine prickly pear (Opuntia macrocentra)

 Another function that the spines serve is that they help certain species of cacti such as cholla to root and spread.

spines of cactus

 Teddy bear cholla (Opuntia bigelovii)

Spines of the Cholla are specialized to detach and attach onto anything that comes to close. There are tiny barbs at the tips which grab on to anything that gets too close. It almost appears as if they ‘jump’ off of the main cactus as they latch on the unlucky recipient.

Spines of the Cholla are specialized to detach and attach onto anything that comes to close. There are tiny barbs at the tips which grab on to anything that gets too close. It almost appears as if they ‘jump’ off of the main cactus as they latch on the unlucky recipient.

**If like me, you are ever unlucky enough to find a piece of cholla embedded in your clothes or worse, your skin – you can use a comb to help pull out the barbs.  When hiking in the desert, it is easy to get them stuck on your shoes.  I usually grab a rock and use it to push off the Cholla segment.  When all else fails, a good pair of needle-nose pliers works.

young saguaro cactuses

 Two young saguaro cactuses are emerging from the shelter of a creosote shrub.

Hopefully, you have a new appreciation for cacti and their spines.  But, it’s still important to be careful because it hurts when you get pricked!

What Plant Where? Beautiful Plant Combinations

Nurse Plants and Cactus

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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 Desert Tree, The Palo Verde

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Large blooming palo verde an 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 palo verde, an iconic tree with their beautiful green trunks and branches.

An Iconic Desert Tree; The Palo Verde

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 planted in groups along a walkway

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

Palo Verde Trees Are Nurse Plants to Saguaro Cacti

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 Palo Verde Flower

 Desert Museum’ Flower

There Are Several Species of Palo Verde

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’).

Grab my FREE guide for Fuss-Free Plants that thrive in a hot, dry climate!

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.

Palo verde Iconic tree

 Iconic tree, Palo Brea

Palo Verde Landscape 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.  

Palo verde in bloom Iconic tree

 Foothills Palo Verde

Basic Palo Verde Maintenance

Pruning for Canopy Elevation and Structural Integrity:

Pruning Palo Verde trees in your desert Southwest garden is a crucial aspect of maintaining their health, aesthetics, and structural integrity. One of the primary objectives of pruning is to elevate the canopy, ensuring it remains well-balanced and visually appealing. This practice involves selectively trimming the lower branches to create a more elevated and open canopy. By doing so, you allow for better air circulation and light penetration, which can promote overall tree health and reduce the risk of disease.

Steering Clear of Hedging and Topping:

While pruning is essential, it’s equally vital to understand what not to do. Avoid two harmful practices: hedging and topping.

  1. Hedging: Hedging involves indiscriminate shearing or cutting of branches to create a uniform, artificial shape. This practice is highly discouraged for Palo Verde trees, as it not only compromises the tree’s natural beauty but also disrupts its growth patterns. Hedging can lead to dense, bushy growth with weaker, more susceptible branches.
  2. Topping: Topping is the severe cutting of the uppermost branches, often leaving stubs or bare trunks. This practice is detrimental to the tree’s health and stability. When Palo Verde trees are topped, they respond with a vigorous burst of new growth that tends to be weak and prone to breakage. Topped trees are also more susceptible to pests and diseases.

The Proper Tree Pruning Approach:

Instead, adopt a thoughtful and strategic approach to pruning your Palo Verde trees. Start by identifying dead, diseased, or damaged branches, and promptly remove them. This eliminates potential entry points for pests and diseases, promoting tree health.

Next, focus on elevating the canopy by selectively pruning lower branches. When selecting branches for removal, prioritize those with narrow crotches or those that cross and rub against each other, as these can weaken the overall structure.

Consider hiring a certified arborist or a professional tree service to ensure that your Palo Verde trees receive the care they deserve. These experts have the knowledge and experience to prune your trees correctly, preserving their natural form and promoting robust, healthy growth.

By following proper pruning practices and avoiding hedging and topping, you can help your Palo Verde trees thrive in your desert Southwest garden. A well-maintained Palo Verde tree not only adds to the beauty of your landscape but also provides valuable shade and habitat for local wildlife while remaining resilient in the harsh desert environment.

Palo Verde is My Favorite Tree

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. Simple amazing!

Fall Rose Tips for the Desert Garden

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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.

How Long Does It Take Before A Saguaro Grows Arms?

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Saguaro cactus

Exploring the Growth of Saguaro Cactus Arms

In the realm of desert flora, the saguaro cactus stands as an iconic symbol of the American Southwest.

The saguaro cactus (Carnegiea gigantea) is a towering, tree-like cactus native to the Sonoran Desert, spanning the regions of Arizona and Mexico. It claims the title of the tallest cactus in the United States, reaching heights of up to 52 feet and boasting a substantial diameter of up to 30 inches. Despite their slow growth, saguaros have an impressive lifespan, enduring for as long as two centuries.

One of the most common questions about these magnificent cacti is, “How long does it take for a saguaro cactus to grow its arms?” There’s a prevailing belief that it requires a staggering 100 years, but let’s delve deeper into the fascinating journey of saguaro arm growth.

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.  

Unveiling the Mysteries of Saguaro Cactus Arm Development

Saguaro cacti (Carnegiea gigantea) are renowned for their impressive stature and distinctive arms, making them a captivating presence in the desert landscape. However, the timeline for the growth of saguaro cactus arms is far more nuanced than the century-long myth suggests.

The Influence of Habitat and Water Availability

The primary factor influencing the rate of arm development in saguaro cacti is the availability of water. In their native desert habitat, where water is a precious resource, saguaros exhibit a slower growth pattern. It’s not uncommon for them to take between 50 to 100 years or even more to sprout their first arms.

Accelerated Growth in Landscape Settings

In stark contrast, saguaro cacti in landscape settings, where irrigation systems provide consistent moisture, tend to grow at a significantly accelerated pace. The abundant water supply encourages more rapid development, and as a result, these cacti often display their distinctive arms much earlier than their counterparts in the wild.

Regional Variations in Growth Rates

Even within the saguaro’s range, growth rates can vary based on regional climate conditions. For instance, saguaros in areas with slightly higher rainfall, such as southern Arizona near Tucson, may experience faster arm growth compared to those in drier regions of the Sonoran Desert.

The Unique Journey of Each Saguaro

It’s important to emphasize that while some saguaro cacti may begin growing arms in as little as 10 to 20 years in well-irrigated landscape settings, others may take longer. Each saguaro’s journey is unique and influenced by various environmental factors and care.

In general, a saguaro growing in its native habitat can take 50 – 100 years to grow arms. In a landscape setting, where saguaro are treated with gentle care, arms often appear much earlier.

I have had many adventures with saguaros and love seeing them in the garden landscape. They look particularly spectacular paired up with an ocotillo.