Managing Ground Vegetation in an Organic Orchard

If you’ve spent time around orchards, you might have noticed that the ground vegetation in organic orchards often looks “messier” than the vegetation in conventional orchards.

A block of galas on our orchard in June of 2024.

By comparison, in conventional orchards, the orchard floor is typically kept tidy using herbicides (under the trees) and consistent mowing (between the trees).

Image of a conventional apple orchard in spring, by ringelbaer from pixabay

In this post, I’m here to inform you that this aesthetic difference does not arise out of neglect! In fact, the greater complexity of the orchard floor in our organic orchard (see what I did there?) is the result of intentional management strategies that follow from organic principles.

Before going on, you’ll need to know some terminology:

Tree row: The part of the orchard floor where trees are growing, which includes the ground underneath the trees and extending out as far as the trees’ longest branches (this area is also called the dripline of the tree, since it is the area where rainwater drips off).
Drive row: The part of the orchard floor which functions as a path for the movement of people, animals, and machinery. Since orchards are planted in rows, drive rows are interspersed between tree rows.

As organic orchardists, our aims are to:

Increase soil organic matter
Increase biodiversity throughout the farm system
Manage pest outbreaks in the most benign way possible

To accomplish these aims, we use two main strategies when managing orchard floor vegetation:

Subtractive management of vegetation in the tree row.
Maintenance of habitat strips down the center of the drive row.

Let’s see what these strategies involve…

Subtractive management of vegetation in the tree row

The idea behind subtractive management is to remove, mow, or prevent from going to seed any vegetation that you want to decrease in abundance in a given place. Any vegetation that you want to increase in abundance, you simply leave alone, thereby allowing it to spread and/or go to seed.

Ambrosia block right after weedwacking in the tree row, June 2022.

For example, we consistently mow grasses and sedges (which have no trouble regrowing) and plants with thorns (hazardous for large mammals and machinery) which pop up in the tree row. On the other hand, plants which are ideal for the tree row, such as white and red clovers (low-growing nitrogen fixers), and henbit (low growing and favoured by bumblebees), are encouraged to flower, go to seed, and gradually spread throughout the orchard.

To accomplish subtractive management, we use electric weed-eaters to do precision weed-wacking of vegetation in the dripline of trees. We do this up to four times per growing season. We also occasionally remove vegetation using tools or hand-pulling, often casually while we’re walking through the orchard doing other things.

Subtracting vegetation from the tree row has numerous benefits: it increases soil organic matter (through decomposition of mown stems and decaying roots), keeps the area around ground-level sprinklers clear, and makes it easier for us to access and work in the trees. It also aids in reducing rodents by reducing their favoured habitat and exposing them to predators.

We rarely add new vegetation (or seeds) into an established orchard floor system, as doing so requires removing the vegetation that is there (without herbicides), which can be extremely labour intensive. It also requires disturbing the soil, which in turn disturbs the community of organisms which already live there.

2. Maintenance of Habitat Strips in the Drive Row

In the rainforest, different layers of the vertical forest canopy provide ideal habitat for different species. In fact, the structural complexity of vertical spaces in the forest canopy is one of the reasons that rainforests are so biodiverse.

Why is this idea important for us? Because in general, the more biodiversity within the orchard the better — not only because of the inherent value of having as many lifeforms coexisting here as possible, but also because biodiversity increases biological control (when beings in the orchard control the populations of other beings in the orchard), which is the most benign method of pest management there is.

This spider (genus Argiope) makes its home in the forest-like canopy on the orchard floor in one of our Pink Lady blocks, September 2022.

One of the way that farmers apply this idea is by establishing hedgerows (walls of trees and shrubs) around a farm’s perimeter to serve as habitat. In orchards, we can take the principle one step further: the more our orchard floor looks like a jungle, with structural complexity in the vertical dimension, the more biodiversity we can support. So, in addition to encouraging hedgerows to grow around the orchard perimeter, we maintain an unmowed strip of natural vegetation down the middle of every drive row.

A habitat strip within a Pink Lady block, June 2023.

This practice significantly increases the amount of vertically-complex habitat that exists in the orchard. Based on calculations made using Google Earth:

The perimeter of our orchard is about 1,500 meters.
The total length of all drive rows within our orchard (excluding the orchard perimeter and main tractor trails) is about 8,000 meters.
Thus, the total length of all habitat strips (hedgerows and drive rows strips combined) in our orchard is about 9,500 meters.
Therefore, maintaining vegetation strips within the drive row increases the length of habitat strips within the farm system by a factor of about 6.3 (9,500 divided by 1500).

We have experimented with different widths for drive row habitat strips, ranging from about 2 feet wide up to the width of the entire drive row (stopping at the tree dripline). Generally, wider vegetation strips mean more habitat, but wider habitat strips can make navigating the orchard difficult. 1 meter wide seems to be a pretty good compromise.

To remove unwanted vegetation on the outer edges of the drive row, we have had success using a riding lawn mower, set up to blow cut vegetation back into the tree row (this technique is called “mow and blow”). Weed-wacking this area works as well, though it takes quite a bit more time.

When practical necessity arises, we do mow the entire drive row. For instance, we always flail-mow prunings in the early spring, and we always mow the entire orchard before harvest.

See, we can be tidy too. Gala block, September 2023 before harvest.

Some lessons learned

It is common knowledge among orchardists that one should never mow (or weed-wack) the orchard floor before petalfall (the time when apple blossoms are shed). Doing so can cause thrips to enter the trees, where they feed and do cosmetic damage to young apples. In our organic orchard, where herbicides are forbidden, waiting for the blossoms to be completely gone can result in some pretty extreme growth. The first weedwacking odyssey of the season can feel like bushwacking, and the hayfever can be intense!

This recurring habitat strip is a favourite spot for wasps and pollinating flies, but can be quite difficult to navigate around. Gala block, May 2022.

It is rarely the case that we want to subtract all of a particular species from a place. Some plants are good to have around, but only in low abundance and/or when they are spaced out. For instance, it is good to have mullein around the orchard, since it functions as a bug hotel, allowing us to monitor what insects are present in a block. However, too much mullein can attracts pests. As a compromise, we try to remove most of the mullein, leaving just a few individual mullein plants spaced throughout each block to serve as insect monitoring stations. Likewise, many plants with thorns are beloved by pollinators, so we remove them from within the orchard where they are hazardous for us, but allow them to remain in surrounding hedgerows.

Over the years of experimenting with these practices, we have also learned (the hard way) that certain tall-growing plants have to removed from the drive row before their stems become too tough and woody in late summer (e.g. mullein in its second year). Otherwise, they become a problem for tractors to drive over, and become very difficult to remove. Plants that become large and woody are ideally always kept at low density in the orchard, and then subtracted before they become a problem.

Another lesson we’ve learned is that some plants should be managed differently depending on whether they are found in the tree row or the drive row. For instance, it is best to subtract alfalfa from the tree row, because it competes too effectively with the trees for water. Since alfalfa is otherwise a beneficial plant to have around (it fixes nitrogen and provides ample food for various insects), we encourage its presence in drive row habitat strips.

Alfalfa with cabbage white butteflies, August 2022.

Conclusion

I hope I have managed to convince you that in organic orchards, ground-level vegetation is best thought of as a complex, life-promoting habitat which helps us meet our goals in stewarding the land. We manage this habitat using ecological principles, aiming to increase soil organic matter, promote biodiversity, and increase the level of biological pest control within the orchard (thereby minimizing the need for less benign interventions). Through the application of subtractive management in the tree row and the maintenance of habitat strips in the drive row, we help steer plant communities to evolve in desired directions. In doing so, we hope to provide a haven for diverse beings to flourish, which helps us maximize the wellbeing crop species which our livelihoods depend on.