"My heart is glad, my heart is high
With sudden ecstasy;
I have given back, before I die,
Some thanks for every lovely tree
That dead men grew for me"
~ Violet Helen Friedlander, Planting Trees
At once infinitely rewarding and altogether unselfish, planting a tree is among the most simple and altruistic acts we can perform. It can also be ill-advised and even destructive in a world full of subterranean pipes and cables. Be it Arbor Day or just another weekend, if you're planting a tree, there are a few things you should know so that your deed remains testament and gift to the future, and doesn't turn into an expensive, catastrophic plumbing problem.
How can plants affect my plumbing?
The major issue with regard to plumbing is root infiltration of the sewer line. When pipes are laid underground, the soil around them has typically been dug out and loosely backfilled. It's much easier to establish roots in loose soil than compacted, so trees will take advantage of such areas if they're available. Roots are also incredibly tenacious in their hunt for water and nutrients, and your home's sewer lateral (the pipe running from the house to the public sewer main) just happens to contain plenty of both.
Once roots find their way in – usually by way of a loose joint in the lateral pipe – the feeding frenzy begins. They continue to grow and travel, compounding their own obstruction by capturing oil and grease, debris and bathroom waste. And blockages might only be the beginning; given a point of entry, even just a crack, tree roots can break through boulders. So a pipe made of PVC, concrete, or clay doesn't really stand a chance. How can you avoid this scenario? You'll need to do your homework.
What can I do to prevent problems?
It's important to know the lay of the land before you break out the shovel. The primary concern is the lateral, but the ground around your home is concealing a network of other pipes and cables, too. Knowing the location of these is key to a successful planting. Your city's public works department should be able to provide you with this information, or you can call 811 (http://www.call811.com) a few days ahead to have utility companies mark the relevant lines in your yard for free.
Once you know what and where to avoid, you'll have either the simple matter of finding a good spot, or an intractable dilemma. It all depends on the location of the lateral, the size of the yard, and the type of tree or plant you want. It could be that the "perfect" spot in your yard – the one you stare at every day through the window, the one that needs a tree – is the absolute worst place you could ever plant. Just try to keep in mind the problems it could lead to down the road: not only is there the shame of neglecting good advice, but a torn-up yard, and a massive bill as well.
Among your available planting areas, you'll obviously want a location with enough water and nutrients for the tree you've chosen. These requirements vary by the tree, and you'll want to get specific on how to keep it happy. It may be helpful to break up and amend some soil around the planting area and away from pipes to encourage root growth in that direction. Remember that roots, like most things, take the path of least resistance whenever possible.
Though it varies with the type of tree, a good rule of thumb for planting distance is to take the height of the mature tree and add 20%. This may not always be practical, so some go with the height alone. Still others maintain that a mere 10 feet from the sewer line is acceptable. We believe the further, the better. If you're on a septic system, avoid planting above the tank or the leach field. Instead, try to find a spot near the end of the line. If you really need to plant something on the field, go small and try to plant between the drain lines.
Note: If you're on a septic tank and plan to plant near a leach field, keep in mind that the effluent/waste can affect the pH of the surrounding soil, which may limit your choices.
In addition to a good planting location, some choose to heavily compact the soil on the sewer-side of the tree in an effort to retard growth in that direction. Root barriers are also an option, and should extend at least 2 feet below the surface, and be at least 5 feet away from both the sewer line and the tree. Rather than encase the roots of the tree, it's recommended that the barrier run alongside the lateral to promote healthier root growth. Others implement barriers using rocks or chemicals. While these can be effective, we advise against the use of chemicals since they may end up harming the tree and surrounding life.
What's safe to plant?
That depends on many factors, but in general, trees with deep root systems are usually okay to plant with some precautions, while those with shallow root systems lead to doom. You'll want something slow-growing and not terribly water-hungry to minimize risk. Don't get too hung up on finding a problem-free tree, though: you should reconcile yourself to the idea that even a small, slow-growing one may need replacement in 8-10 years to stall a march into your pipes.
The Arbor Day Foundation has a helpful tool (https://www.arborday.org/trees/) for choosing a tree, while California Polytechnic State University has an even more powerful one (http://selectree.calpoly.edu/ attribute_search.lasso) that allows you to select specific constraints and attributes ranging from salinity tolerance to fruit color. To find a tree that shouldn't cause too many plumbing problems, select "low" for "Root Damage Potential".
By selecting an appropriate tree and location, you can minimize the risk to your sewer line, and rest easy knowing you've done your best to ensure your effort will reward yourself and others for years to come. Whether it's a passerby admiring the tree's beauty, a child climbing it, or the next grateful tenant who doesn't have to tear up their lawn to replace a pipe, their joy is your thanks for taking the extra bit of time to get things right.