By Eric Morse
When it comes to digging, transporting and transplanting trees, there is no better tool than a tree spade attachment paired with a skid-steer, compact-track or all-wheel-steer loader. This solution accomplishes all three tasks, minimizing manual labor by allowing the loader operator to dig, transplant and package trees without leaving the cab. Using a tree spade attachment on a compact loader makes digging and moving trees more efficient, since it is easy to navigate the constrained work areas often found at nurseries or when moving trees on residential or commercial properties.
In order to select the best tree spade attachment for the application, it’s vital that operators know what type of blades to use on a tree spade, what size of tree spade is needed, and the required set-up for the loader.
Tree spade blade configurations
There are three types of tree spade blade configurations: truncated, cone and modified. The type of tree spade blade to use depends on what the contractor is trying to accomplish and the type of soil in which the tree spade is working.
“Truncate” means to “lop off.” The truncated blade “lops off” the bottom of the cone-shaped hole that the spade digs to create a pot-shaped root ball. The lopped-off bottom of the tree spade allows the tree and its root ball to easily fit in a pot or burlap bag and to be stored or displayed in an upright position.
Truncated tree spades in the industry are 22 degrees. What this means is that if a line 90 degrees perpendicular to the ground was set next to the tree ball, the line of the slope from the top of the tree ball to the bottom would be 22 degrees from the line perpendicular to the ground.
“The 22-degree truncated blade is the tree spade with the narrowest profile,” said Bryan Zent, marketing manager for Bobcat Company. “This makes the truncated blade a good option when working in tight tree rows on a nursery, because it can get to where it needs to work without damaging nearby trees in the row.”
Truncated blades dig best in heavy, clay-type soils. Truncated blades are the widest blades used on a tree spade, which makes them the hardest with which to penetrate the ground. Truncated blades also produce the root ball with the heaviest weight.
The cone blade tree spade produces a root ball that is almost pointed, with a narrow bottom. Cone blades produce root balls with sides of 30 degrees. Although 30-degree baskets can be used in nurseries, root balls on cone blades do not stand as easily as balls produced by truncated or modified blades. For this reason, cone blade tree spades are best for moving a tree from one location and transplanting it in another. “The steep angle of the cone blade also makes it an effective tool for pruning roots in a nursery,” said Zent.
The narrow bottom of the cone blade produces less resistance than truncated or modified blades, meaning the cone blade can work in the widest variety of soils, from soils that are hard-packed to sandy. The cone blade is the best option in sandy soils because it minimizes the amount of soil that spills away from the roots. “When soil comes away from the root, the root is exposed to air and can dry out,” said Zent. “Dry roots create greater stress on the tree and the cone blade lessens this stress.”
The modified blade is a transitional blade that offers the best qualities of the truncated and cone blades. Like the truncated blade, the bottom of the root ball is lopped off so that the tree can stand for display or storage. The modified blade has an angle of 25 degrees, which is a steeper angle similar to the cone blade. Like the cone blade, the modified blade will exert less resistance on the soil when working, making it easier to use than the truncated blade.
The root ball that the modified blade produces is wide, not deep, which means it retains a large area of the tree’s roots. “The modified blade is popular with nurseries because it excels at harvesting large trees,” said Zent.
Modified blades should not be used in sandy soils, but are the best option in loam or clay soils.
The 10-to-1 ratio
There is an easy rule to use when determining what size of tree spade to use to dig and transplant a tree. Multiply the diameter of the tree trunk by 10 inches to get the size of the tree spade to use. For example, a tree with a trunk diameter of three inches requires a 30-inch tree spade.
An important thing to remember about the 10-to-1 ratio is where to measure the diameter of the tree trunk. The diameter should be measured six inches up the trunk from ground level. Trees with diameters larger than four inches should be measured 12 inches up the trunk from ground level.
Compact loader set-up
According to Zent, before operating a compact loader with a tree spade, the machine must be properly equipped to carry and use the attachment. Bobcat requires that rear stabilizers are used when operating a tree spade attachment on a compact loader. The rear stabilizers raise the loader off the ground. This transfers the weight of the loader to the front of the machine, where it is needed to maximize the digging performance of the tree spade. This weight transfer is helpful when working in tough soil conditions. “Using the rear stabilizers to transfer the weight helps to maximize the diameter of the root ball,” said Zent.
Bobcat also recommends adding counterweights to a compact loader to improve the productivity and performance of the tree spade attachment.
“Tree spades can make efficient work out of digging, moving and transplanting trees, but like any other piece of equipment, they have to be sized and used properly,” said Zent. Nursery operators and other users should make sure to use the right type of blade for the type of soil and the job being performed. Size the tree spade attachment based on the 10-to-1 ratio and the diameter of the trunk of the tree. Use rear stabilizers and counterweights if they are required or recommended by the loader or tree spade attachment manufacturer.
Eric Morse is with Two Rivers Marketing, Des Moines, Iowa.
Article provided by Bobcat Company, Fargo, N.D.