by Olivia Saunders, UNH Extension Field Specialist, Carroll County
If you’re a grape grower, raspberry producer or have a few blueberries, you may have wondered what grasses are best suited between your fruiting rows. Ideally, you want the ground between your perennial crops covered with something slow growing, with a low maintenance requirement, not a harbinger for pests, and one that does not compete with your commercial crop for water or nutrients.
By growing a cover crop you are enhancing the underground microbial diversity. This may sound well and good if you care about biological diversity, but what does that mean for your bottom line? How does that impact your plant productivity and ultimately your yield? If you take a microscopic look at your soils underfoot you will find a diversely functioning mega-city. By adding a cover crop (as opposed to bare soil) you are enhancing the habitat for these soil organisms, like channeling earthworms (of which there are many types), the champion decomposers fungi, beneficial nematodes, mineralizing bacteria that enhance nitrogen uptake, the list goes on. You are providing a food source for these guys who in turn provide fertility, break down organic matter, move nitrogen molecules from point A to point B, and compete with soil born pests like Phytophthora or Verticillium. Some growers have reported fewer leafhopper and mite problems due to increased predator-prey relationships when a cover crop was grown. Studies from Oregon State have demonstrated that soil community enrichment was correlated with leaf phosphorous content, and changes in soil biodiversity associated with nitrogen mineralization and availability.
Permanent Grasses: There are a number of fine fescues commonly used for turf production that are also well suited for perennial fruit production, these include: Chewings fescue, creeping red fescue, hard fescue and sheep fescue.
As a group, fescues can tolerate low fertility & low pH, droughty soils, and shaded conditions. They will not thrive in: hot, humid conditions; wet soils; high-traffic areas such as athletic fields; and high rates of nitrogen fertilizer. During periods of heat or drought they will become dormant, and start growing again as cool temperatures return. The fine fescues are more favorable than tall fescues in perennial crop production.
Grass alley with vegetation-free strip: This is the most common system here in NH. This allows for tractor access between the fruit rows, prevents erosion, and improves water infiltration. The 2.5-3 foot zone directly under the tree or berry is managed with herbicide or clean cultivation, this eliminates competition for water and nutrients in the rooting zone of your crop.
Mow and blow: A technique where you mow the grass alley and blow it under the crop. This may be advantageous if you grow a legume and want to supply nitrogen to your cash crop, or to provide weed control with the mulch. Not ideal if your row middles have weeds that have gone to seed.
A note of caution: Organic growers interested in growing a legume within their perennial beds to capture and add nitrogen should be aware of potential risk. Legumes also attract Tarnished Plant Bug (TPB), which affects both small fruit and vegetable crops, even at low densities. Vetch and clover species as well as a number of common weeds may attract TPB to your perennial crops. If you have a meadow or plantings that could host TPB near perennial fruit plantings, mowing should be timed carefully to avoid the time of flowering for fruit crops; the displaced TPB can migrate into the fruit crop and damage can result.
Mowing: how often you need to mow will be determined by your site, seasonal weather and the grass species. At minimum, you should anticipate mowing 1x month, although more often is recommended. Grass mixtures marketed as “no-mow” will need to be mowed at least a few times a year.
What to avoid: Any high stolon producing grasses which will creep into your crop over time. These include Bentgrass, Zoysiagrass, or the forage-type grasses like Timothy, tall fescue, orchardgrass, perennial ryegrass or bromegrass. Highly productive grasses should be planted on only the most vigorous sites with deep soils.
Avoid planting perennial crops into an existing field without proper weed control. If planting into an existing field, there is a high likelihood of being out competed by creeping grasses like quackgrass, which could significantly depress yields. Once the crop is established there are limited herbicide options. At minimum, one year of cover cropping or tillage should occur prior to planting.
Mulches: By applying a thick layer of organic mulch like compost or wood chips, you increase the risk of vole related damage to fruit trees. If your site is excessively droughty or sandy and you are looking to conserve moisture & control weeds, organic mulches may be appropriate. A small layer of compost that gets worked into the soil to add fertility every few years should not be a problem. A thick layer of organic mulch however, is the ideal habitat for voles. In New Hampshire, blueberries are the exception and are typically mulched with wood chips to provide weed control.
Establishing the crop: If desired, you may want to add a nurse crop of oats in the seeding mix at a rate of 5 pounds per acre to help establish a covering in the first year to prevent erosion
Want to know more? Here are a few helpful factsheets-