It took the entire summer to figure out the logistics, but Iāve finally done it: Iāve successfully planted a group of flowering crabapple trees on artificially raised ground in my orchard, protecting their roots from the frequently waterlogged subsoil below.
Have you ever set your heart on planting trees in a specific location, only to realize the soil conditions arenāt ideal? Thatās what happened to me. Iād latched onto the idea of planting crabapple trees in two parallel rows on a slope, with the notion of watching them form a beautiful walkway of pink blossoms every spring.
In June, I dug the holes in advance of ordering the trees. Everything was perfect ā¦ until the rains came.
I quickly discovered that my holes didnāt drain particularly well. Situated as they were on sloping ground, the bottom two holes in particular were problematic. Whenever an inch or so of rain fell, water would migrate down the sloping terrain, fill the holes, and sit there for days on end with minimal draining.
I tried a few experiments to improve the soil drainage, including digging deeper holes to try and break through the hardpan layer, but my efforts were unsuccessful.
Ultimately, I decided to employ a different approach. I would raise the ground level at the bottom of the slope and plant the two lowermost trees at an artificially elevated level.
A Challenging Task
Such a task is more challenging than it sounds. Trees need a lot of room to spread their roots. And the volume of soil required for raised plantings is substantial.
My flowering crabapples will eventually grow their crowns to a circumference of 20 feet, so each āraised bedā needs to be at least 20 feet by 20 feet to provide sufficient space for a mature tree.
Furthermore, I wanted the tops of my crabapple rootballs to sit about 8 inches above the surrounding ground, which created an imposing mathematical outcome. In order to raise a 20-by-20-foot area 8 inches high, I needed 264 cubic feet of quality topsoilāand thatās for a single tree.
To put this in perspective, filling a 4-foot-by-8-foot trailer with 12 inches of topsoil yields a load of 32 cubic feet. So I would need 8.25 loads to plant one tree.
The need for an abundance of topsoil isnāt the only challenge. Ironically, planting trees on raised ground means youāll have to pay extra attention to keeping it watered. The soil underneath might contain plenty of water, but your raised bed will likely drain quickly, and you donāt want your tree to suffer from drought while itās getting established.
Erosion is also a concern. How will you keep your raised ground in place and prevent rainfall from washing youāre carefully-placed topsoil away? Retaining walls built of rock, brick, wood, etc. may be necessary to keep the soil contained.
Work in Progress
My plantings are still a work in progress.
I was able to source a lot of topsoil from the edge of a wooded spot on my farm. But since my immediate goal was getting the trees in the ground before autumn, I didnāt build my raised plantings to their full extent. Instead, I made them 5 feet by 5 feet or so.
This provides just enough room for the trees to grow next spring while I continue bringing in topsoil throughout 2021.
To limit erosion and keep the soil in place, I got creative. Rather than build temporary retaining walls, I instead took a shovel and chopped up sections of sod around the planting areas. I flipped them outward and upside down (away from the holes) to form perimeters of well-rooted soil still partially attached to the ground by the roots of grasses and wildflowers.
With the sod chunks serving as surprisingly firm barriers, I was able to fill the interiors with a few small wagonloads of compost, packing it all down tightly to secure each tree in place.
Best of all, I wonāt need to remove the chunks of sod when I expand the raised plantings next year. Theyāll simply decompose and become an organic part of the soil.
Ultimately, Iām happy with the way my experimental planting project turned out. Iām confident my crabapple trees will appreciate sitting above the waterlogged ground, and Iām looking forward to adding more soil and building the true retaining walls in 2021.
I wish I could use pure compost for the projectāIāve got plentyābut alas, Iām concerned it would be too rich for my trees. The last thing I want to do is burn their roots after going to such great lengths to avoid drowning them!