Growing the Texas/Mexican Madrone
People say that Texas Madrones are hard to cultivate. Indeed they can be, but it is certainly not impossible. In Alpine Texas I have seen multiple large, beautiful specimens in people's yards. They are always growing in protected locations however, like the north or east side of a house, were they won't get cooked in the hot summer afternoons. This makes sense when you keep in mind that the few places that they can be found in Brewster and Pecos County, for instance are relictual habitats like narrow washes and canyons, protected from the hot afternoon sun.
No doubt like many of the members of subfamily Arbutoideae (of the blueberry family, Ericaceae), They harbor specific kinds of mycorrhizal fungi and they have the root morphology to do it, consisting mostly of many fine fibrous root hairs that provide ample surface area for the fungi to colonize. That said the exact species of fungi have most likely not been genetically sequenced or analyzed, which is yet another tragedy of how understudied so many aspects of Texas botany and ecology are.
Dr Michael Powell at Sul Ross University states that the limiting factor is for the most part the very narrow window of water that they require when young. It is very easy to let them dry out And it is very easy to overwater them to the point that they easily rot. The trick is keeping the soil moisture level within the boundaries of that fine window in between two wet and too dry. Others have stated that products like root shield can inoculate them with the fungi they need, but others state that it is not necessary. Depending on how hot and dry the climate is, they are probably best with morning sun and shade in the hot afternoon. They do like water when they are old, but they do not like swampy soil.
At the University they are grown in narrow tree tubes. With a large volume of fast training soil it seems safer to prevent them drying out while also preventing them rotting. The fast drainage prevents rot in the larger soil volume prevents drying out quickly. Perhaps a mixture of half organic substrate mixed with a quarter pumice and a quarter pine or cedar bark chips (which are organic but also resistant to fungal attack) would be the key. Vermiculite might also help since it holds moisture but is not easily eaten by fungi. Keep in mind that most pathogenic fungi get their start eating organic matter that is already dead and decaying and then gain enough strength to attack living tissue, like the roots of the madrone. If the roots are inoculated with the beneficial mycorrhizae, then attack by pathogenic fungi is probably less likely, since mycorrhizae have been known to “ward off” pathogenic fungi in various settings. This makes sense, since there is a self-interest on the part of the fungi in protecting its own food source (forgive the anthropomorphizing, lol It just helps in an explanatory sense).
Whatever the specific code is to growing madrones, It is important to keep trying. This is such a great and beneficial plant for pollinators and wildlife and should be revered in Texas horticulture as many wild plants continue to succumb to drought and a changing climate.
Things to remember when growing Arbutus xalapensis:
Avoid root disturbance at all costs. If you grow a few seedlings together in the same pot keep in mind you cannot separate them at any stage during their later growth. Just let them grow together and accept that if you might die or they might all grow together to form a single tree. It's not worth disturbing the roots and breaking those fine sensitive root hairs.
Protect young trees from deer. If a tree is damaged when it is young, it will resprout leaves but the leaves will likely wither and die. No one really knows why this happens but they do not recover from deer browsing when young. It is worth culling deer when possible unless you have the help of a local mountain lion.
The most important thing to consider when growing Madrones is to keep the soil in that fine and narrow window between too much moisture and too little. Do not water them unless you have picked up the pot and felt how heavy it is, since The weight of the pot changes according to how much water is in the soil. Sometimes you can eye the top of the soil level too but that will only give you an idea of the top inch of moisture content, when it is the roots that are most affected by overwatering or underwatering.
All photos and auto-correct typos my own.
