The Hole Truth About Planting Holes

by Joran Viers

Which is better: planting a five-dollar tree in a fifty-dollar hole, or planting a fifty-dollar tree in a five-dollar hole? Don’t worry, it’s a rhetorical quiz and the answer appears below. No points will be deducted.

What I’m trying to get at is a question that was at the heart of a three-day workshop I attended last fall, sponsored by the New Mexico Chapter of the Colorado Nursery and Greenhouse Association. The workshop brought together what my colleague and mentor Andrew Lisignoli calls the “partners in chlorophyll”; that is to say, people involved in the planning, growing, planting, and maintenance of trees and smaller plants. Landscape architects to landscape contractors, and all points in between.

There are many reasons trees in urban settings suffer, and in an arid city like Albuquerque, those seem to be compounded. If I could boil it down, however, the root cause (pun intended) is often a lack of water in the leaves. Notice, I didn’t just say a lack of water, but rather the inability of the water to get to the site of photosynthesis where it is most critically needed for tree health and growth.

Sometimes the problem is with the tree. Current nursery production methods using plastic containers have a strong tendency to produce young trees with roots that hit the side of the pot and then turn, continuing to grow at the edge of the root ball. They may grow all the way around, they may grow up and around, they may grow back through the root ball, but the gist is that an unnaturally twisted and confined root system is developed. If part of that mess includes roots that grow all the way around the container, they will create “stem-girdling roots”. These are, simply, roots that surround the young trunk, and they develop size as the tree grows, and then years later the trunk meets the now-large root, which doesn’t give way. The trunk, unable to continue growing outward, is effectively strangled by the root. The tree declines and then dies, sometimes actually breaking off just below ground level at this constriction point. The problem – water moves up little straw-like cells in the sapwood (the wood just below the bark), and those get crushed against the root, with the consequence of less and less water reaching the leaves.

Sometimes the problem is with the hole. Urban soils are notoriously hard (“compacted” is the term we like to use), and roots cannot grow well into hard soil. So, even if water is applied to those compacted soils, few roots are there to take in the water, and the leaves don’t get what they need. Tree decline ensues.

Sometimes the problem is with the irrigation design. Tree roots grow shallow and broad, and they need to be watered broadly. Drip systems or bubblers that provide water right at the trunk get the tree started, but soon the amount of water, and the placement of that water in the soil, are not what the tree needs. Tree decline ensues.

Often, the problem is some combination of the above: poor quality root system in a small hole in compacted soil, insufficiently irrigated. Welcome to the life of many Albuquerque trees; a life, it should be noted, that is much shorter than we want or expect, even by urban tree standards. Trees that don’t live long don’t get big; trees that don’t get big don’t provide all the wonderful benefits that we know they can give us – shading, reduction in energy use, carbon storage, air pollution reduction, storm water amelioration… all of these benefits come with trees of a mature stature. Too many of the trees planted in our lovely desert city never make it to that point. Too many of them die within a few years of planting, and in that case all the money, time and effort put into the tree up to that point is wasted.

So, what is the answer? Well, it’s a trick question, because the right choice is a fifty-dollar tree in a fifty-dollar hole. Too often designs call for large trees but fail to provide soil volume and site preparation specifications that will actually succeed in the long run. Too often nursery stock comes to us with root defects, many of them hidden, which will kill the tree no matter how well designed and prepared the site is. Too often the contractors’ bottom line gets in the way of the extra time and effort needed to plant the tree well. We’re all to blame.

Let’s take it a step further, then. How do we overcome these limitations?

First, we must be willing to demand, and then pay for, quality planting stock. No amount of further discounts will make a bad tree a good investment. The nurseries are caught between their own financial success (i.e. staying in business) and the buying public’s unfortunate ignorance of what it takes to grow a good tree.

Second, but no less important, those artistic souls who design our landscapes need to understand what it will take to get the living part of their composition to cooperate with the design. Just because the tree fits in that tiny spot on paper doesn’t mean it will work in the real world. Biology trumps aesthetics every single time.

Third, we need to understand that trees are large plants with lots of leaves, and they will need a lot of water. They will need that water throughout their lives – very few sites in Albuquerque have enough natural soil moisture to support tree growth. But not all irrigation is equal, so understanding how roots grow and function is important. Knowing what soil conditions will support that root function is important. Knowing that gravel mulch is a bad thing for trees is important (I could rant on that one issue for hours…).

I guess it all boils down to education – we need to educate ourselves and each other on the reality of what it takes to grow decent trees in a desert city. It ain’t easy, folks! If it was, we wouldn’t be second in the nation for tree canopy loss. You can use the internet and search out this information for yourself! Just be sure to steer clear of magic bullets – they don’t exist. If it sounds too good to be true, it is.