Trials in Orchard Understory Plantings and Management
John Knisley, Madelia, MN
Since 2010 we have been experimenting with various plantings and non-mechanical means to keep fruit tree rows free from being encroached upon by grass or other potential tree-resource competitors. Through these different trials we have found some real “winners” and a few that I would not try again. Generally speaking, we have been planting higher density tree rows with spacing anywhere from 4-8’ between trees and on dwarfing and semi-dwarfing rootstock (B9, G11, and some M7, and G935). The really dwarfing rootstocks have been known not to compete well with grasses and therefore we have taken efforts to keep the base of the trees free from extra competition. The results are as follows:
Bocking #4 Comfrey:
This variety does NOT self-seed and has worked amazingly well under both larger and smaller trees! It should be understood that when you are planting root cuttings from comfrey you will not achieve full growth until the 2nd or 3rd years, and therefore must put some extra effort in the first year to keep grass out. Ideally you are planting the comfrey in the tree rows when you are planting the trees, keeping the growth of the comfrey in-line with the growth of the tree. Consider spacing the comfrey plants anywhere from 12-20” from the base of the tree and on both sides of the tree. In a year or two the comfrey plant will have matured and will smother out grass very well around the base.
Comfrey produces a taproot and does not tend to be rhizomatous (unless you cut the root) and forms a nice, neat clump. When fully grown a mature plant will easily cover a 3’x3’ space or more, with multiple growth periods during the warm season. In addition to the re-growth, the plants produce beautiful purple flowers, of which you will find many different pollinators, especially bumblebees. We have been practicing cutting the growth, after flowers have fallen, to force new growth more quickly – this creates more biomass under the tree and seems to keep the grass at bay the best. Comfrey cuttings can get rather expensive if you are planting 2 cuttings per tree in a long tree row, so consider starting your own comfrey bed in another location, let it grow for a few years, and you will have all the comfrey cuttings you want for a long time. We started our bed five years ago and continue to harvest hundreds of cuttings each spring, all started from the original 20 cuttings we purchased. Comfrey is both a medicinal plant and a nutrient miner, because its long tap-root brings up nutrients from deep in the ground and can make it available to your new tree. Lastly, a friend has recently told me that comfrey is a good indicator of soil moisture levels; if the comfrey wilts, it's too dry for your tree; if it's moist enough, the comfrey will be green and rigid.
We all know we enjoy fresh rhubarb in the spring time from our little secret patches, so why not expand that patch and bring it into the orchard? Rhubarb has nearly all of the same features as comfrey (deep tap root, multiple leaf flushings in a season, and flowers that pollinators and parasitic wasps like) but has a slightly less dense canopy. Rhubarb can spread its leaves fairly wide so I would suggest planting no closer than 16-24” from the base of the tree. Like comfrey, you can cut the leaves to force new growth and increase biomass, but there is a point in the summer where you no longer want to continue to cut the leaves so it can restore itself before winter. Typically we stop cutting our rhubarb around July. The roots of rhubarb can also be divided and re-planted in the spring time around new trees in your orchard. On top of all of this, it’s a potential value-added crop that can also save you time in weeding around trees.
Cover Crops (Buckwheat, Chicory, Oats, Radish, Crimson Clover, etc.):
Cover crops can be a good choice for smothering grass if you are preparing your tree row a year or more ahead of planting. The density of the cover crop depends on the density of your seeding; the key here would be to go heavier on the seeding. The cover crops noted above winter-kill and will needed to be re-planted annually. We have struggled with cover crops after the trees are planted as they can actually act somewhat like grasses and take away from the trees because of their root density. These are definitely an affordable pre-tree planting option for most orchards.
We have been using wood mulch in trellised rows for a number of years and there are positives and negatives.
Positives: provides good grass suppression if mulch is deep enough (6” or more) and holds moisture very well. We have not watered a tree in any of the rows with wood mulch after planting. Placing wood mulch also starts you on your journey towards a healthy forest ecology in your orchard. Lastly, as the mulch breaks down, it provides a perfect planting medium for your other herbaceous perennials or herbs.
Negatives: the wood mulch tends to break down rather quickly and needs to be re-applied annually in our case, which can be a labor intensive. If you do not get the mulch thick enough you will have grass invading your row, so this needs to be monitored and weeded. I suggest using wood mulch for the first year and at the same time planting your herbaceous perennials – the mulch keeps the row free of grass and allows your perennials some time to grow without competition.
Various Herbs (Chives, Walking Onions, Oregano, Sage):
Of all the herbs we have planted around the trees, those in the onion family seem to do the best with grass competition and annual growth. Chives clumps nice and be planted right next to the tree; walking onions will form a nice little colony around your tree, but may not suppress grass like you want. Sage and oregano are perennials that are fairly low-spreading, but again do not compete well with grasses. So, I suggest planting a mix of herbs with comfrey or rhubarb to get the maximum benefit in the tree row.
The goal at our farm is to create a healthy ecosystem for both the trees and other creatures that live here – AND to reduce the extra steps needed to keep a farm running. Often, we see the benefits from these various management techniques in a year, but sometimes it takes more years before you truly see the end-game. We hope this article can give you some food for thought when considering your own orchard or that new plot you were thinking of planting.
Feel free to contact John and Brooke Knisley with any questions or feedback at Alternative Roots Farm.