Planting trees

I recently spent a fun morning planting trees in my neighborhood with the Newton Tree Conservancy.

The NTC is replacing street trees that have died

    The NTC and the city had made all the preparations, leaving us volunteers with the happy task of actually planting the young trees, each with a trunk diameter of about 1 to 2 inches. Our director of urban forestry, Marc Welch, had chosen a mix of species, minimizing the risk that one pest could wipe out all the new trees. Homeowners signing up for street trees in front of their houses had agreed to some conditions: they’d be present on planting day, they’d provide a hose and water access, and they’d be responsible for watering the trees for the next two growing seasons.

    The city team dug a hole where each tree would stand. Beside each hole they left a sapling wrapped in a large plastic bag, to keep it from drying out, a small pile of bark mulch, and a watering bag. You may have seen these cleverly designed green bags around the base of newly planted trees. The bag zips around the trunk and has a double lining, creating a pouch that holds 15 gallons of water. 

A tree watering bag can be filled up with a hose

Tiny perforations at the bottom of the sack allow water to drip out gently over five to seven days, keeping the soil moist.

    Our job as planting volunteers was to make the hole fit the roots of each young tree. Some had spreading roots, others headed deeper into the ground. We were careful not to bury the trunk’s flare, the widening where the trunk meets the roots. That’s because planting too deeply starves the roots of oxygen. 

Central Park. A trunk should flare at the base like this.

 We needed to deepen some holes and replace soil in others. Once the tree was in the hole, a popular way to judge how high it was sitting was to lay the handle of a spade across the hole. We had to make our holes wide enough so that the roots had room to spread out.

    One person held the tree trunk straight, while another gently shoveled soil into the hole. When the soil in the hole looks poor, it’s tempting to enrich the backfill with compost or other amendments. Research shows that it’s better for the tree if you don’t. If the roots find enriched soil in the hole, they’ll stay there and not grow out into the surrounding soil. We returned the original soil to the hole without embellishment.

    We mulched around the trunk of the new tree, being careful to leave a space around the trunk and form the mulch into a saucer, not a dome. Over-mulching prevents needed air and water from reaching the roots.

 

Far too much mulch. Four inches is the maximum safe depth.

Then my planting partner Hal showed me how to set up the watering bag and fill it with water. 

     The weight of the water tended to tilt the trunk at first. Walking by the trees this week, I see that with the watering bags less full, the trees are upright. It’s great to see the young trees settling in.

Felix checks out one of the trees we planted