Tree
Myths and Facts
Lesley and Gil Smith, certified
arborists, Arborsmith
November 8, 2005
Shagbark Hickory
Bud
(photo courtesy of Sue Auerbach)
| Myth 1: | Tree roots are much deeper than grass roots. |
| Fact: | Tree roots are very shallow, so even shallow trenching can seriously injure or kill a tree. In Riverwoods, with its heavy clay, tree roots are typically only 8 inches to 10 inches deep. Construction, including trenching and use of heavy equipment, is the biggest cause of tree injury in Riverwoods. |
| Myth 2: | Tree roots extend roughly to the tips of the branches. |
| Fact: | Tree roots extend well beyond the branch tips – up to two or three times the overall branch spread of a tree. That means that even minor construction activity well beyond the extent of the tree’s branches can injure tree roots. |
| Myth 3: | Short-term parking of vehicles or equipment near a tree will not seriously injure the tree. |
| Fact: | Tree roots are injured by soil compaction. Soil compaction can occur through a one-time event, such as moving a heavy vehicle across tree roots, or a series of seemingly insignificant events, such as periodic disturbance of the soil layer around a tree. |
| Myth 4: | Grass around a tree won’t injure a tree, since in a natural environment trees grow in grassy prairies. |
| Fact: | Because both turf grass and trees have shallow roots, grass competes with trees for moisture and nutrients. Prairies are composed of native grasses with much deeper roots. In nature, trees tend to grow in forests and grasses grow in prairies. When the forest and prairie meet there is competition for moisture and nutrients. |
| Myth 5: | Mulching around a tree is good. |
| Fact: | Proper mulching around a tree is good. The mulch must not be contact the tree trunk, should be no more than 3 to 4 inches deep, and should extend 6 or 8 feet from the tree. It is not necessary to mulch trees in a forested area, since the trees provide their own mulch by dropping leaves. Those leaves cool the soil, trap and preserve moisture and provide nutrients to the tree. The general goal in transplanting and growing trees should be to emulate nature as much as possible, since that’s the environment in which trees have evolved. |
| Myth 6: | Mulching robs the soil of nitrogen and other nutrients. |
| Fact: | There has been no scientific confirmation of that widely held belief. The type of mulch is much less important than mulching itself. Inexpensive mulch is fine. |
| Myth 7: | When a tree is injured, it will show discoloration or drop its leaves. |
| Fact: | Trees react strongly to injury, but the reaction is slow to appear. Tree injury is generally not apparent for three to five years after the injury. By the time trees show injury, significant decline in health has occurred. |
| Myth 8: | Oak trees can live up to 200 to 300 years. |
| Fact: | That’s true, but in Riverwoods there is enough stress on trees that a 150 year old tree is very old. In addition, trees in Riverwoods are about 30% shorter than trees in more natural areas. |
| Myth 9: | Temporarily placing construction soil fill near a tree won’t injure the tree. |
| Fact: | Soil fill injures roots by compacting the soil around roots. In addition, because the soil in Riverwoods is heavy clay, the soil fill may trap so much moisture that it will drown tree roots. |
| Myth 10: | Cutting tree roots is always bad. |
| Fact: | Cutting tree roots never helps a tree, but sometimes is necessary. For example, it is necessary during transplanting a tree. It may be necessary during construction. The best way to cut tree roots is to slice them with a sharp implement, to avoid shredding and tearing. If tree roots will be affected during construction, “root pruning” – slicing tree roots before excavation – will reduce tree injury. |
| Myth 11: | If it's green, it's good. |
| Fact: | Obviously this isn’t the case. Poison ivy is green, but few people want it for their property. Buckthorn has beautiful, glossy, long-lived green leaves. It is undesirable because it is highly invasive – it crowds out other plants with aggressive propagation and intense shade. |
| Myth 12: | Buckthorn can be controlled by cutting. |
| Fact: | Generally, heavy infestations require not only cutting but careful application of an herbicide such as “Roundup”. The herbicide should be applied immediately after cutting, by painting it on the cut. Care should be exercised to avoid herbicide contact with other plants, and with you. |
| Myth 13: | Agricultural herbicide use is more extensive than residential use. |
| Fact: | Three times as much herbicide is used residentially than agriculturally. |
| Myth 14: | When planting trees, it’s best to plant so the top of the rootball is at ground level. |
| Fact: | Because of the heavy clay soil in Riverwoods, sometimes it is better to place a new tree in a slight berm to prevent roots from drowning. |
| Myth 15: | It’s better to plant larger trees rather than smaller ones, for quick results. |
| Fact: | Larger trees generally do not transplant well. It typically takes about one year per inch of tree trunk diameter for a tree to recover from transplanting. It’s best to avoid transplanting trees larger than about three inches in diameter. Possibility Place, in Monee, is a good source for healthy trees for Riverwoods. |
| Myth 16: | The best trees for Riverwoods are oaks, since they are dying out. |
| Fact: | While oaks are having difficulty competing with faster-growing shade tolerant species, variety is still important. In addition, oaks don’t tolerate shade well. Good trees for shaded areas include redbud, ironwood, musclewood, witch hazel, and sugar maple. Swamp white oaks tolerate wet, heavy soil, but need light. Some evergreens, though not native to Riverwoods, may thrive, including white pine and junipers. Hemlocks do not like Riverwoods soil, and are deer food as well. |
| Myth 17: | Frequent watering trees during a drought is good for trees. |
| Fact: | In general, frequent watering is not desirable. Heavy watering, once a month or so during drought, is better for trees. If the soil is dry an inch or two below ground surface, watering is appropriate. Watering can occur at any time, as long as the Village permits it. |