Q&A
If you’re going to add plants around a street tree, make sure they’re not too thirsty and have shallow roots.
CreditVictoria RobertsQ. Will planting flowers and bulbs in a tree pit seriously harm a city street tree?
A. Probably not, at least after the tree's first few years. By then, the tree should be getting its water not just from the small area of soil within the sidewalk cut but also from its spreading root system.
New York City posts an approved list of tree species for urban planting, many of which are drought and pollution tolerant and will grow in narrow spaces.
In the best circumstances, attractive plants can keep people and dogs from walking on and compacting dirt around the tree trunk. When the plants wilt, it can serve as a reminder to water them and the tree.
But the Brooklyn Botanic Garden and the New York Botanical Garden offer some strong warnings. The extra plants in the tree pits should be varieties that are not too thirsty and have shallow root systems. Some good choices are annuals like impatiens; ground-cover varieties like periwinkle; and small bulbs like crocuses and miniature daffodils.
Avoid ivy, which drinks a lot of water, climbs and strangles the tree, and shelters rodents.
The top inch of soil around the smaller plants should be gently loosened, but deep cultivation should be avoided, so that the tree roots are not harmed. Most important, the soil level should not be raised to pamper the undergrowth.
When too much soil is piled up, the air and oxygen are pressed out, starving the tree roots. Moist soil can also make the bark rot, leaving it vulnerable to diseases and pests.
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