The Pennsylvania Horticultural Society plants hundreds of trees each year. This past spring, volunteers planted 1,100 trees throughout the city of Philadelphia, and in the fall they plan to plant even more. In total, the group has planted over 3,000 trees since it started its tree planting program five years ago. The goal for these trees is to improve Philadelphia’s urban environment by adding shade, reducing the heat island effect, reducing pollution, increasing carbon sequestration and more.
Heaving thousands of 2-inch-caliper trees around the city would have been prohibitively expensive and time-consuming if it wasn’t for the age-old planting technique of bare root planting that is less expensive per tree, and allows volunteer participants—including children—to lift trees using just their hands.
“Bare root planting is God’s gift to the volunteer planter,” said Mindy Maslin, Pennsylvania Horticultural Society’s project manager, who oversees the tree planting projects.
|Photos courtesy of Cornell university.|
|Volunteers transplant trees on State Street, Ithaca, N.Y|
Bare root planting was widely used to plant trees before the late 1950s, and is done using young trees that are dug and stored without any soil around the roots. It is a technique that has fallen out of favor with the advent of the ball and burlapped (B&B) technique and container planting that began in the late ’50s and early ’60s, which allows the tree to survive longer out of the ground.
The advantage of costs and labor to plant bare root trees are particularly appealing to municipality tree planting programs, which are usually limited by tight budgets. Trees can be purchased at one-third of the cost of the traditional ball and burlapped trees, and bare root trees can be easily transported—even using volunteers’ vehicles—rather than hiring large trucks and manpower to transport and plant the trees.
“We pay about $35 per bare root tree … the same tree would cost $150 if it were B&B,” said Maslin. Bare root trees that are around 2-inch caliper weigh about 15 to 20 pounds; a similar 2-inch-caliper tree with a 24-inch-diameter ball would weigh about 300 pounds. “This makes a huge difference in how many trees volunteers can plant, and you can even involve kids in the effort,” said Maslin. Tree planting can be done by simply using shovels. To save even more money, municipalities can also band together to purchase trees wholesale and then distribute the trees at a centralized location.
The bare root advantage
Bare root trees are not only less expensive and lighter to transport, they also establish faster than ball and burlapped or container trees. Bare root transplants come with up to 200 percent more roots because the harvesting machinery for bare roots takes up a larger root system than the tree spade system used for B&B. Root stress is one of the major reasons that tree transplants fail, and trees with bare roots often are left with the fine, absorbing roots when they are harvested, giving them a better chance of surviving.
The risk of burying a tree too deeply is also lessened with bare root planting, since the root flare is easily visible; the root flare is often covered by soil in ball and burlapped trees. Girdled roots can also be spotted more easily and remedied when the tree is in a bare root state.
The downside to bare root planting
While the advantages are appealing, there are downsides to planting bare root trees. Larger caliper trees (exceeding a 2.5-inch caliper) do not do well transplanted using the bare root method; and some species of trees, regardless of size, do not make the transplant well in bare root. Trees must also be planted when the tree is dormant, in early spring or late fall.
The biggest disadvantage to transplant-ing bare root trees is the short window between the time the tree is out of the ground and the time it is planted. These trees must be planted within a few days of harvesting. “If these trees freeze, or the roots dry out, the game is over,” said Maslin.
While packed wet straw around the roots or dipping in mud has traditionally been the solution to keeping the roots moist, researchers at Cornell University have created a more effective way using hydrogel, a synthetic, nontoxic slurry that looks like table sugar when it is in its dry state and can hold several hundred times its weight in water when wet.
“Dipping roots in the hydrogel slurry keeps the roots moist and in good shape for a week or two as you work out the logistics of planting,” said Nina Bassuk, director of the Urban Horticultural Institute at Cornell University who pioneered the technique with fellow research-ers. Bassuk said that the hydrogel slurry was developed by Cornell in the ‘90s at a time when municipal budgets were being cut and many cities and towns needed to go back to the bare root method of planting to save money. “Dipping in hydrogel and then bagging the roots in plastic buys time,” said Bassuk.
Another disadvantage of using bare root trees is the scarcity of these types of trees for purchase. Not all species are available in nurseries that carry them, and not many nurseries have bare root trees available at all. Maslin said that her Pennsylvania-based organization must order bare root trees from nurseries as far away as Oregon (although she has found closer sources in New York state and Iowa). “We purchase the trees wholesale and they are shipped via refrigerated truck,” she said.
As municipality budgets shrink even further with the current state of the economy, nurseries might see a thriving market for bare root trees, said Maslin. “We’d love to see bare root growers in our state. That’s what is missing—local growers.”
The author is a freelance writer from Keene, N.H.
|Trees Species and Bare Root Planting|
|Easy to Plant Bare Root|
|Scientific Name||Common Name|
|Acer campestre||hedge maple|
|Acer x fremanii||Freeman maple|
|Acer platanoides||Norway maple|
|Acer pseudoplatanus||sycamore maple|
|Acer rubrum||red maple|
|Acer saccharum||sugar maple|
|Acer truncatum||Shantung maple|
|Catalpa speciosa||cigar tree|
|Cercidiphyllum japonicum||katsura tree|
|Cornus mas Cornelian||cherry dogwood|
|Cornus racemosa||gray dogwood|
|Gleditsia triacanthos||honey locust|
|Gymnocladus dioicus||Kentucky coffee tree|
|Malus spp.||crab apple|
|Parrotia persica||Persian Parrotia|
|Platanus x acerifolia||London Plane Tree|
|Prunus ôAccoladeö||Accolade flowering cherry|
|Prunus virginiana||Canada red chokecherry|
|Pyrus calleryana||Callery pear|
|Quercus bicolor||Swamp white oak|
|Robinia pseudoacacia cultivars||black locust|
|Sorbus intermedia||European mountain ash|
|Syringa reticulata||Japanese Tree Lilac|
|Tilia cordata littleleaf||linden|
|Ulmus Americana and elm hybrids except ôFrontierö elm|
|Moderately Difficult to Transplant Bare Root|
|(Note: With the remaining species, there is better success transplanting in fall.)|
|Scientific Name||Common Name|
|Acer buergeranum||Trident maple|
|Alnus glutinosa||European alder|
|Corylus colurna||Turkish filbert|
|Crataegus crus-galli inermis Thornless||Cockspur hawthorn|
|Crataegus viridis ôWinter Kingö||Winter King hawthorn|
|Prunus subhirtella var. autumnalis||flowering cherry|
|Quercus robur||English oak|
|Quercus rubra||northern red oak|
|Quercus velutina||black oak|
|Tilia tomentosa||silver linden|
|Zelkova serrata||Japanese zelkova|
|Difficult to Transplant Bare Root|
|Scientific Name||Common Name|
|Crataegus phaenopyrum||Washington hawthorn|
|Liriodendron tulipifera||tulip tree|
|Ostrya virginiana||American Hophornbeam|
|Quercus coccinea||scarlet oak|
|Quercus imbricaria||shingle oak|
|Quercus macrocarpa||bur oak|
|Quercus prinus||chestnut oak|
|Taxodium distichum||bald cypress|
|Ulmus ôFrontierö||Frontier elm.|
|List courtesy of Nina Bassuk, director of the Urban Horticultural Institute at Cornell University, Ithaca, NY|
How to Dip Roots in Hydrogel
Get a large vat, like a plastic horse trough, to mix the hydrogeland water. Follow the manufacturer’s instructions for root dips(Cornell recommends 15 ounces of hydrogel per 25 gallons ofwater). Let the hydrogel/water solution sit for 30 minutes to onehour; the consistency should be that of thick gravy.
|Photo courtesy of the Cornell University Urban Horticulture Institute.|
|Dipping roots in hydrogel slurry.|
Dip the tree roots in the hydrogel slurry and do not shake. Putthe roots of the tree into a large pleated plastic bag (use pleatedbags so that the roots won’t poke through the side). Tie the bag orknot it to keep in the moisture.
Store the trees in a cool, shaded location until they are ready tobe planted. Do not wait more than one week after the hydrogel dipto plant.Ask for a fine grade of hydrogel (1,000 micron particle sizeor less), and do not purchase starch-based hydrogel; ask for synthetic,cross-linked polymer hydrogel. Starch-based hydrogelbreaks down too fast for bare root planting purposes.