Thinking outside the pot

Steve Mercer’s family hasn’t been in the nursery industry for decades, but the way he sees it, that’s not a disadvantage.

“I’m not a second or third generation nurseryman,” Mercer said. “We’re in the greenhouse business, and we’re just starting to do some nursery, although we’ve been propagating our own nursery stock for a while. But I don’t have any bad habits, so to speak, from being in the nursery industry for generations. I don’t have any preconceived notions of how things are supposed to work.”

Mercer runs Preston Greenhouse in Louisville, Ken., where he grows a wide variety of annuals, vegetables, perennials, trees and shrubs, and operates a garden center.

He believes the fact that he doesn’t have several generations of family in the nursery business frowning over his shoulder, telling him that he’s not doing something the “right way” is a boon. It allows him to see persistent problems with clear eyes.

For tree planting, Mercer uses root-pruning fabric bags. The American Standard for Nursery Stock for trees grown in bags is different than the standard for balled-and-burlapped. For a 4 inch caliper shade tree, the standard for B&B is a 44-inch root ball. The same tree in a growbag would have a 28-inch root ball. Mercer believes growing in bags saves the buyer of these trees in shipping, labor and replacement costs. The grower can plant more trees per acre because wide aisles are unnecessary, or interplant a few rows of holly or boxwood between two rows of shade trees.

The problem
The biggest complaint most nursery growers have with growbags, Mercer said, is that you have to put them in the ground and return later to plant.

“They don’t like doing that,” Mercer said. “The day they want to plant trees, they want to plant trees. They don’t want to have to plan it out six months ahead.”

Mercer decided the reason using growbags is more difficult than it could be was not having a planter that works the way nurseries are used to working. Conventional wisdom had nursery crews using an auger to dig the hole for the growbag, then dropping that dirt back into the bag, and planting the bag back into the hole. The problem with that system is that the soil is unsettled after using the auger. Disturbed dirt creates a planting problem.

“You can’t put a plant in it right away,” Mercer said. “You have to let the rain settle that dirt, or else the first time it rains you’ll go out there and all your liners will be listing at a 45-degree angle, because the dirt you put back in that bag is completely unsettled.”

Mercer decided the best way to improve the process would be to eliminate the auger part of the equation.

“By using an auger, you are putting all that loose dirt back into growbags,” Mercer said. “That precludes the grower from being able to plant a liner right away. The best way to eliminate that problem is to use a hydraulic tree spade and take a plug out of the ground rather than take all that loose dirt out of the ground.”

The solution
“Necessity is the mother of all invention,” Mercer said. To satisfy his need for a better system, he started with a hydraulic nursery spade that is used for field potting. He had it custom-built by Dutchman Tree Spades.

With this configuration you don’t need a gate on the machine because you’re not planning to back away or pull into a tree to dig it. An adjustment is lined up in the center of the machine that allows the placement of a steel tube, which can be adjusted up and down for the various sizes of trees you want to plant. For a 4-inch pot, you have a 4-inch diameter tube. If you want to plant a 3-gallon pot, you have a tube that is as wide as a 3-gallon pot. Those tubes actually stick down below the frame of the tree spade, so when the operator pulls up and sets the machine on the ground, that tube has already cut a dibble hole before you even run the spades in the ground.

Then you run your three spades into the ground, and pick them up. At that point, an operator on the ground slips a custom-sewed growbag onto the blades. The bag is tapered to the same angle as the blades on the spade.

There is a spring clip on the top of each blade, which holds the bag on the machine long enough that the operator on the ground could step back away from it. When the operator sets the machine back into the same hole and retracts the blades, and picks up on the machine, it picks up the plug of dirt that was in the dibble hole.

“You don’t get near the settling that you would if you used an auger to punch a hole to a 12-inch depth and you have all this fine dirt you’re putting back in the hole,” Mercer said.

Now, the grow bag is in the ground, full of soil, with a hole in the middle of it, ready for a liner. Then when the loader operator picks up and pulls forward, a crew behind him starts knocking plants out of containers and planting them in those dibble holes.

“It’s a fairly simple operation,” he said. “We’re still fine tuning it, but the concept is sound. It allows us to plant a liner in the bag right away as opposed to having to wait six months before we plant it. I’m surprised that somebody didn’t think of this a long time ago.”

With this system, a four-man crew should be able to plant 1,500 trees a day – all bagged with a liner in them.

“It’s a one-pass deal,” Mercer said. “When you get to the end of the field you have a row of trees planted in the growbags, and you’re done.”