As I view landscapes, while driving through our suburbs and cities, and hear people’s questions, I see and hear serious mistakes – many that risk the health and survival of trees.
Some are based on myths and old-fashioned ideas, because in previous decades folks just didn’t know certain horticultural principles, or we didn’t have some of the plants and products we now have.
Some mistakes are ill-informed or copycat errors, because nobody took a horticulture course or did the homework. Sometimes mistakes happen because people don’t think about plants as living things and instead treat them like furniture. Not everybody is into plants.
What do all these mistakes have in common? Stopping the practice or fixing the mistake early will prevent trouble – or plant death – later. And continuing to do that same thing will definitely cause dire and costly problems. Let’s stop these mistakes now.
• Using tree trunks like telephone poles: Today I saw 12 heavy storm windows propped against a small tree, with a “For Sale” sign on them. They have been there for days, through wind storms, and surely their movement is scraping bark off the tree. I wanted to – but dared not – leave this note: “When you lean heavy things against a tree you are damaging the bark and the delicate vascular system just beneath it. This is somewhat like severing your arteries, and it will harm the tree’s health.”
A tree trunk is also the wrong place to nail or staple signs, banners or hooks for stringing lights. Every time you pierce the bark you are making a wound – a place where insects or diseases can enter. For the same reason, a tree trunk is not a romantic place for drawing a heart around sweethearts’ initials or honoring the Class of 1999. Those are nice sentiments expressed in a harmful way. Rent a billboard.
• Treating soil like gravel: Why do people tend to pile cinder blocks, lumber, stones, wood piles and mountains of mulch on the soil under trees? It is not as if the tree will keep those things dry. Nor is the soil under a tree better at bearing weight than, say, a concrete or gravel driveway, or perhaps a wooden platform out on the side lawn – where you can reseed after the project is over.
When you put weight on the soil under trees, you are compacting the soil and damaging tree roots. Unlike old beliefs, most tree roots do not grow downward – the taproot image.
Most tree roots are in the top 15 inches of soil, way out past the drip line, including lots of delicate ones in the top few inches. Heavy objects are smashing those roots as well as the air and water-holding capacity of that soil. Good soil is a porous substance, including air, water, minerals, organic matter and living organisms. It’s not gravel or concrete.
Once it is compacted, soil takes many years to regain its tilth. Even one pass with a vehicle under a tree does damage. And please, no parking under trees. You may not see damage from soil compaction and root damage immediately, because trees take a couple years to show severe stress, but these mistakes cause serious harm.
• Burying the bark: When it is covered by soil or mulch, tree bark cannot survive; it rots. Tree bark is made of cells that are different from the cells surrounding plant roots. That is why mounding the mulch up a tree trunk – “volcano mulching” – is not only useless and silly looking, it is also going to rot the tree trunk.
When you look at a planted tree, you should see the start of the “root flare” – where the root begins to reach outward – above the soil line. When you plant a tree, keep that root flare slightly above the soil line. And then do not let the mulch touch the tree trunk.
Instead, start the mulch a few inches out from the trunk, and limit the depth to 3 inches. Over the years, continue to pull back the mulch whenever it crowds the tree trunk. You don’t like layers of turtlenecks and woolen scarves tied around your neck, do you? Let the tree breathe.
• Not watering or shallow watering: This passive error can be just as deadly as taking an ax to the tree; it just takes longer to kill. A recently planted tree – “recent” meaning two or three years – must have your help to get water during dry periods, because its root system is still very small, relative to the size of the tree.
A 6-foot (small) tree may need 10 or more gallons of water per week, and rainfall rarely provides that much, even in spring. Ball-and-burlapped trees have had over 90 percent of their roots cut off. The water must be supplied to that small root area, regularly and deeply enough to penetrate all the roots.
Tree Gators (those green bags), if filled regularly, are great tools for supplying water. Daily, shallow watering is irrelevant. Deep, weekly watering is usually better, in proportion to the size of the root ball. Dig with a shovel sometime, after a rainfall or watering, to see how far the water penetrated.
• Strangling by staking: In windy areas it’s often necessary to stake recently planted trees. If it is not windy, staking is not a requirement; tree roots become anchors that hold trees in place. If you stake a tree, be sure to mark the calendar a year from planting with the reminder to remove the stakes and wires, tubes or ropes. Wind is natural; strangulation not so much.
A word to the wise: Now that we agree on these points, please be tactful as you pass the advice on to your partner or the neighbor with the rock pile under the elm tree. They just didn’t know.
Sally Cunningham is a garden writer, lecturer and consultant.