GNV expert gives tree planting advice

City of Gainesville horticulturist Eric Kohnen has planted thousands of trees in just the past two years alone.

His goal is to retrace his steps and record the exact locations of every tree he has ever planted using the locator app, ArcGIS.

“It measures the exact pinpoint of where all your plantings are,” said Kohnen. “You record the date, species, and height of the planted tree.”

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That way he can keep track of the growth and the impact of his planting efforts.

“Trees are really important,” Kohnen said, as he prepared to plant an 8-foot tall white oak tree recently at Evergreen Cemetery.

Kohnen is building an arboretum that will host 100 trees of all different species at the historic municipal cemetery in Gainesville. An arboretum is a specialized botanical garden that features trees. 

Once he is done, visitors will be able to learn all about each tree by scanning a QR code.

As the City prepares to distribute hundreds of free trees this Earth Day at Northside Park, 5701 NW 34th Street, from 9:30 a.m. to noon, Kohnen shares recommended tips for planting trees. This is his method for ensuring a tree is off to the best start possible so its growth continues for decades and even hundreds of years to come. 

Kohnen, who studied horticulture at Iowa State University, said tree selection is the first step in the process. 

He chose to plant a white oak tree in an open area at the cemetery because he said it would provide abundant shade and brilliant colors throughout the season.

Step by step, here is how Kohnen approaches planting a tree:

City of Gainesville horticulturist Erik Kohnen tree height for planting
  1. First, check the tree nursery stock for a quality tree with full branching all the way around, good width (caliper) on the trunk, and check for roots not too tangled around in the bucket.

  2. At the planting site, snip out the weeds and remove anything that might compete with the growing tree. Make sure there are no utility lines overhead that could be impacted as the tree matures. Check that no cables or pipes will be damaged by digging in the chosen spot. Neighbors can call 811 or 800-432-4770 or put in an online request at my.sunshine811.com — Sunshine 811 to do so. 

  3. Set out two empty buckets the same size as the pot the tree came in to hold the dirt from the hole.

  4. The width of the hole to dig for the tree should be about 9 to 12 inches beyond the pot width. This will enable the lateral roots to spread out more easily. Use your shovel width for reference and easy measuring.

  5. Mark the circle and remove the top grass layer by cutting squares in the top grass, then shake excess dirt off when removing the grass layer. According to Kohnen, that topsoil is full of nutrients. Returning some of the removed grass back in with the fill dirt is okay as well.

  6. Match the hole depth to the depth of the pot the tree comes in. The white oak Kohnen planted came in a 15-gallon bucket which is about 18 inches deep. The trees to be given away on April 22 come in 3-gallon buckets which measure about 12 inches tall.

  7. If you dig at the walls of the hole with the shovel facing backward, you can go wider more quickly quicker, Kohnen demonstrated.

  8. Be accurate in measuring the depth by using a mark on the shovel or a measuring tape. This will help you avoid placing the tree in the hole multiple times. The tree base should be flush with the ground.

  9. Before setting the tree base into the hole, Kohnen removes the tree from the pot and rubs down the roots and loosens the soil. This stimulates the roots that might be tangled up in the pot and helps them spread out easier.

  10. Also, use the shovel to make little divots in the wall of the planting hole so the soil enables the lateral roots of the tree to venture out.

  11. Place the tree in the newly dug hole. As you return the soil to the area around the tree, compact the dirt with your feet. Some say shovel in loose soil, but Kohnen emphasizes that rain on the loose soil can make the tree shift as it settles and the tree could start to lean. Compacting the soil will make sure the tree remains nice and straight. “Stomp it all down with your feet,” Kohnen advises. “Fill it halfway then compact it and put the rest into the top.”

  12. Check to make sure the soil level doesn’t cover the very base of the tree, the trunk flare.

  13. Finally, add mulch and create a berm around the tree making sure the mulch is not touching the tree base.

  14. Kohnen uses City-composted mulch and first clears four to six inches away from the trunk because mulch can harbor insects, pests, diseases, etc. Leave bare soil next to the trunk. The berm will function as a way to retain moisture when water is added. 

  15. Add two 5-gallon utility buckets of water to the tree base. “I let the water pool up and when the ground absorbs it, I give it another drink,” Kohnen said.

  16. And finally, Kohnen recommends to prune at planting to ensure the tree won’t need corrective pruning next year. “Pruning makes a tree grow how you want it to grow,” he said as he backed away to see the branch distribution and balance of the newly planted white oak. Pruning is about preserving the structure and integrity of a tree. “I might take off some lower lateral branches as it grows,” Kohnen said. He left them for now. “It helps the tree gain caliper as it grows.”
City of Gainesville horticulturist Erik Kohnen water tree

The now 8-foot tall white oak reaches about 100 feet when it matures and its location at Evergreen Cemetery falls within the southernmost range in which white oaks naturally occur,” Kohnen said.

It will become a beautiful shade tree with bright red leaves in the fall and should grow 2 to 3 feet each year.

“It’s a fast grower,” Kohnen said, adding that the white oak tree will provide shade, color and acorns for wildlife.

He invites all neighbors to Northside Park this Friday to pick up their free trees (limit two per household) from 9:30 a.m. to noon.

“We are a Tree City,” Kohnen said. “Let’s make Gainesville a littler greener.” 

For additional tips from GRU on tree safety, click here.

City of Gainesville horticulturist Erik Kohnen with white oak in pickup

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