Vachellia xantholophaea: Is this really the best choice for my small garden?
A bit of background
Many of us will recall the words from Rudyard Kipling's story of The Elephant's Child, who was told by the Kolokolo bird to 'Go to the banks of the great grey-green, greasy Limpopo River, all set about with fever-trees,....'.
Why Fever tree? It was a common occurrence for early travelers and pioneers to contract a bad fever when traveling through areas where the trees grew and the trees were thought to be the cause of the fever. The fever of course was Malaria. In a cultural twist, the bark of the trees was traditionally used by the indigenous population to treat fever.
This then, is the home of the Fever tree. Hot and dry in winter, hot, wet and humid in summer. Here they are in their element, soaring up to 25 meters high with a spread of 12 and more meters across, invariably living near a source of summer water. In winter, the pans in which they often stand dry up, the rivers and streams on whose banks they grow, recede to a trickle and the trees take their winter rest.
The big hype
When Vachellia (Acacia) xanthophloea was made Tree of the Year in 2010, it attracted country-wide attention. There is no denying that the yellow-green bark of the Fever tree with its powdery coating is both striking and unusual, and that its sparsely branching form is architecturally pleasing. It did not take long for the wholesale and retail nursery trade, encouraged by gardening publications, websites and public demand, to respond to the growing market.
It is my personal opinion that media articles overlooked the essential suitability of this tree for its use in diverse situations. Without these limitations being clearly stated, the Fever tree has been made available to the uninformed public for use in conditions where it is simply not suitable.
Is this tree the best choice for my garden?
If you have a large garden where you have space to plant a wide variety of trees and you can plant a Fever tree a distance from your living area, you probably don't need to read any further.
If your property is less than 1 000 square meters, read on. Going on the assumption that you have limited space and can only plant 2 to 5 trees in your garden, you need to choose carefully. Remember you have to live with the tree for years to come.
Let's consider some of the facts as they relate to a city or town environment.
How big will it grow?
As mentioned above, in its natural environment, the tree can reach up to 25 meters tall, so if you have a similar climate such as in KwaZulu-Natal, you can expect it to become a very large tree indeed.
If you live in Gauteng or other summer rainfall area with no frost or mild frost, you can expect it to be a great deal smaller. The amount of water available to the tree in summer will be the deciding factor here and my guess would be anything between 8 and 12 meters.
In areas where regular heavy frost is experienced, it is unlikely that the tree will survive its first couple of years, unless wrapped and protected. Once it is too big to protect, it may be partially or completely killed.
From the photos I have seen of Fever trees in the Western Cape with its winter rainfall and hot, dry summers. it would appear that they do not grow excessively tall, possibly due to the generally dry conditions during the prime growing time of summer. I would really be guessing at future size. Most of the trees have been planted within the last 5 - 10 years and have not yet reached maturity, so there is no yardstick with which to make a prediction.
The most important point to consider here is the size of your property. This is not a small tree.
Are the roots invasive?
All Vachellias have a tap root so the automatic assumption is that their roots are therefore not invasive. On the whole this is true.
However, all trees with tap roots also have a network of sub-surface roots, some larger than others, that are utilized for water and nutrient supplies. The Fever tree, being a water thirsty tree, has a more vigorous sub-surface root system than many others and as it ages, these become thicker and stronger, and also travel a great distance from the tree. Shallow watering may result in some of the roots developing close to the surface of the soil, which could cause a problem in later years.
How far away from my house can I plant it?
After you have considered the size and root system of the tree, consider this:
The fever tree is a thorn tree. After three or fours years it will begin to drop twigs. On the twigs are thorns. Big thorns. Thorns that can even penetrate shoes. If there are children or pets around, the ground below will have to be closely monitored to prevent injury. Watch your feet if you walk below the tree and check the ground before you to sit beneath it. Deeply embedded thorns are both extremely painful and can be a serious source of infection (so says the voice of experience!).
While the tree is young be vigilant of little hands that may clutch a branch and wary when walking past the young tree, to avoid a side-swipe from a thorny branch.
So how close can I plant the tree from my house?
For safety, well away from pathways, pedestrian traffic, braai areas, the swimming pool and playing areas.
I've been told that the Fever tree attracts birds.
In its natural habitat and presumably in urban environments, Fever trees are used by some bird species for nesting as the thorny branches provide security Other birds are likely to make use of the tree for perching or resting. Insect eating birds will come to feed but the tree has nothing to offer seed, fruit and nectar eating birds.
Can't I just prune it to keep it small?
You can, but you will forfeit the sparse, long limbs that are so fundamental to the beauty of the tree and you will alter it's natural shape - which is one of the reasons you wanted it in the first place. When any plant is pruned, you stimulate it to produce more branches which may result in more debris falling to the ground.
Is it suitable for a container?
I have had a few queries about this but was not able to find any concrete examples or reports of whether the trees are suitable for container growth.
Growing trees in containers causes the plant to become in effect, a Bonsai, albeit quite a large one, so I researched the use and suitability of the Fever Tree as a bonsai. All the sites I found that even mentioned using the tree as a bonsai indicated poor results. Almost all attempts to grow the tree in reduced size failed and those that were initially successful died within a couple of years at most.
My impression is that it may grow in a container for a few years but will not sustain this growth once it has become pot bound.
Is the tree prone to pests and diseases?
In its natural habitat, no more than the usual caterpillars that may denude it once a year and insects in general that are dealt with by the local bird life.
In suburbia, the outlook is not always so assured. Reports of ant, aphid and whitefly infestation are well documented. Unfortunately the bird and insect predators are unable to make inroads into these infestations and chemical methods may have to be applied.
Since the popularity of the Fever tree in suburban situations has grown, so too have reports of various diseases from which the trees have succumbed, increased. Particularly evident is a canker that attacks the tree and which is invariably terminal. (Admittedly, most of the queries I have had about this disease have come from the Western Cape - something to do with the winter rains perhaps.)
Should I reconsider my choice?
Once again, if your space is limited, look a little further.
There are dozens of smaller, indigenous, non-invasive, wild-life friendly trees to choose from. Trees that provide an all in one attraction: nectar bearing flowers for sun birds and butterflies, fruits for the fruit and seed eaters and the insect eaters will arrive to feed off the insects attracted by the flowers and fruits. If you choose a specimen from your own natural region, you will have some added advantages: it will be water wise, it is already familiar to the wild-life and, as it does not have the stress of adjusting to an unnatural climate, it is unlikely to suffer from pest infestations or disease.
Please, don't get me wrong. I have great respect for the Fever tree. I would love to have one in my garden. I even tried. I bought into the hype. It wasn't successful. I mulched and watered and protected it as best I could through our dry summer. It looked better after the autumn rains. Then I turned my back on it for a couple of weeks, we had a berg wind and the next time I looked I had a stick.