The Benefits and Disadvantages of Cover Crops in Your Orchard

What are the benefits and the disadvantages of planting cover crops around fruit trees? Can cover crops on an orchard floor help prevent fruit trees from climate change? Those are just a few of the questions I discussed with  Christina Curell, Cover Crop and Soil Health Educator at Michigan State University. You can listen to the entire hour-long interview by clicking on the podcast player below. This interview has been slightly edited for clarity.

what are cover crops?

CC: Cover crops are crops that are planted at a different time or used for a different purpose than our main crop. So, for orchard trees, it might be grasses and legumes that we would plant when we are not actually actively harvesting or working in our orchards.

why do we plant cover crops?

CC: We plant cover crops for various different reasons. We do it for the environment. We do it to enhance biodiversity in the microflora of our soil. We do it to increase soil infiltration of water. And we plant cover crops because they can help prevent flooding issues. Cover crops can decrease leaching and runoff of both nutrients and chemicals. And they also can create wildlife habitat in instances when we need it or to attract honeybees and other beneficial insects.

can cover crops combat climate change?

CC: Cover crops can be helpful in dealing with climate change. If we look at some of the patterns in the last several years, we've seen an increase of huge rain events. We may be getting the same amount of precipitation during the year, but instead of a nice gentle rain throughout the growing season, the rain is coming at once within 24 to 48 hours. We're seeing massive amounts of precipitation leading to a lot of flooding.

In those instances, where there are cover crops in the system, those cover crops can actually hold the excess water.  The water will infiltrate through the soil and it can be held in that root zone of cover crop plants. So the water is there when our cash crop needs it. So that's one of the ways that we're seeing that cover crops increase water holding capacity.

how do cover crops prevent flooding?

Oh, I've seen it in my own my own fields.  Last year when we had a hard spring, those fields that didn't have cover crops on them were muddy. They were wet. You really shouldn't be farming on wet fields. In the fields that had cover crops, the water infiltrated down through the soil and ran off the fields. The fields with cover crops dried faster.

can cover crops prevent soil erosion?

CC: When you're looking at huge rain events or snow events, we see a lot of soil movement through runoff. If we have nothing growing in the soil, there is nothing to stop that water and some topsoil from running off into our lakes, rivers, streams, or ditches, or anywhere. Then that soil is gone. We've lost that good rich, highly organic topsoil. But cover crops will actually prevent soil from being washed away. They will hold that water and soil in place. And that is really important for all producers of any crop.

can cover crops have a negative effect on on fruit trees during a drought?

CC: Cover crops can have a negative effect on fruit trees during a severe drought. So you have to really be careful on the cover crops you choose. One of the things that we work with in a perennial system is putting in a cover crop that will hold that water in the soil and actually move it down into that subsoil, where the tree roots are located. That way the water is available to the trees when they need it.

These best cover crops for this purpose will have deeper roots than grasses would probably have. So yes, cover crops can steal the water in a drought situation. But the key is to make sure that your trees’ roots are deeper and that they can actually suck up the water first. The key is to match the cover crop with your crop itself, and we can do that.

is it safe to plant cover crops under fruit trees?

CC: If your fruit trees are established and they have a good root system, the cover crop will not hinder nutrient uptake or water uptake. The tree is going to get the nutrients first, before the cover crop. But I don't recommend planting cover crops close to young fruit trees.

how close can cover crops be planted to fruit trees?

CC: I very rarely recommend that fruit growers put their cover crop right up to the base of their trees. I like a little bit of bare soil around those trees. That helps with pest and disease control.

If I was going to use a cover crop in an orchard, I would recommend a low-growing one, like a low growing grass and legume mixture.

I like a legume and a grass mixture because the legume is going to help with the nitrogen fixation and the nitrogen production, and the grasses have slightly deeper roots. So, I might look at a low growing mixture of white clover with the short growth grass.

can cover crops attract pests to orchards?

CC: If you've got a lot of moles, voles, or mice or any other animal that might nibble at the bark and girdle your trees, you might have a problem. That’s because these pests can create their habitat and live in the cover crops.

So in instances like that, I check if the farmer has issues with pests and if they have a good handle on keeping all of those mammals away. If that’s the case you can try a cover crop. But a lot of times I'm a hesitant because cover crops can cause pest issues, and I don't want that to happen.

can cover crops protect fruit trees from deer?

CC: There are instances where we are planting "trap crops" of cover crops around orchards. We do very specific plantings to keep deer or other wildlife out of the orchard blocks.  We're actually training the deer to come to a certain area where they'll have food year-round. So, we plant that trap crop away from the orchard so that the deer will have something else to eat other than our fruit trees’ bark and branches.

We plant crops that they really like. So, we'll plant some grasses and forages like the type we would use for cattle feed. We would include some grasses that they really like, oats and high value forages. We will put in things like oil seed radish, turnips, rapeseed, canola.

Those “trap crops” will give the deer some feed throughout the winter so that they stay out of the orchards in the winter. That prevents the deer from harming the bark of the fruit trees. It prevents them from chewing or gnawing on the trees. They're actually eating that food for them.

We sometimes put the trap crops around the orchard blocks, like a barrier, hoping that the deer and other wildlife don't even go through it.

One caution though. In Michigan, we have issues with TB in our deer population. So, these trap crops could increase the probability of that disease being transferred in our food systems. TB is transferred from nose-to-nose contact when they're feeding and it's on bait piles and things like that. So, you must be really careful and make sure that if you're going to do something like that, local laws allow you to do it.

can cover crops attract pollinators and beneficial insects?

CC: You can actually do some cover cropping for pollinators. But you've got to manage those plantings carefully because cover crops will become a weed problem if they're not managed.

Why are cover crop mixes useful?

CC: If you want to do a cover crop monoculture, that's fine. Just understand that those grasses at some point may become dormant because we have cool and warm season grasses. Also, a monoculture of grasses may, after a few years, get kind of patchy. So we might have to go in and re-seed them.

If you have a mix of different cover crops, you will usually have something growing all the time. So even if one of the cover crops is going dormant, there's actually something else growing. And if one plant is thinning out and getting patchy, another cover crop will hopefully take over and fill in those holes in the system.

So that's why in a system like orchards, having two different cover crop species is a good thing. It's not required. I can work with anybody if they would rather just do a straight grass or straight legume. Management is easier with a monoculture because you're only dealing with one plant. But it depends on what you want and how long you want to go between having to replant it or re-seed it.

how are cover crops different than weeds?

CC: A common question that I get is, if you don't plant a cover crop, weeds will come in. So why can't we just let the weeds go to cover the soil. Why do we need to plant a cover crop?

The answer to that is, when we put in a cover crop, we are actually looking at the benefits of that plant, just not covering that soil. So there are a lot of plants out there that grow, but they may not have any other benefit. They may not be nitrogen fixing. They may not have a lot of biomass that's going to produce organic matter that is going to hold that water. That's why we use cover crops for those other benefits in the system.

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how do you choose the best cover crop for your climate?

You have to find a trusted local resource. There are Cover Crop Councils throughout North America that people can go to. In Michigan, we're part of the Midwest Cover Crop Council, and so is Ontario. So there's a group of provinces and states that have formed a council and there's information for each state.

The Midwest Cover Crop Council actually has a selector tool. You can go in and say what you're growing, when is it growing, what you want out of the cover crop. Then the tool will give you pointers on what cover crops you should be using. There's a Western Cover Crop Council for the provinces and states in the West side of North America. There's a Northeastern Cover Crop Council too.

These are groups of farmers, researchers, and government officials that talk about cover crops and try to figure out how it's going to fit into your rotation. But again, it's a lot of trial and error. And for those of you familiar with Michigan, we are surrounded by the great lakes and I'm on the Western side, I'm on the Lake Michigan side in the Northwest part, and what grows for us in Michigan will not grow for those people on the other side of the state, just because we have different climates and we have different soil.

how do you choose cover crops for different soil types?

CC: Different soil types will handle cover crops in a different way. And people laugh at me, but I say that for cover crops, Google is our nemesis. You google a cover crop, and you read how wonderful they are! But they may not work for you.

Some cover crops are weeds in some States. Some growers like hairy vetch, which is a cover crop that is widely used. But for a lot of states and provinces it's a weed that actually will kill seedling crops.

Online, everyone loves buckwheat. But buckwheat is my least favorite because it's a weed. Once it gets established, you have to be really careful because it'll take over and it'll out-compete and kill everything else out.

So, you've got to really be careful in choosing the cover crop and look at what works for you locally for your crop and for your location.

how do you prevent cover crops from becoming invasive?

CC: You need to know the lifecycle of that plant. Buckwheat's a weed and so is hairy vetch and other hard seeded plants, because once they flower, they have a hard seed and the seed is set.

So, when it flowers you're actually reseeding! For instance, in Michigan, buckwheat is an annual crop.  It's a warm season crop and does not withstand cold weather. So, it won't survive a frost. However, if that seed has been produced and it's still viable, it'll come up the next year. The same with hairy vetch. So, you need to know the life cycle of your plant before you plant it.

Then there’s annual rye grass.  In some States and Provinces, it is considered an invasive weed. It's resistant to a lot of our chemical herbicides. It will take over.  It's really hard to kill.  It's an annual, but it will survive if the seed has been set and it will become a weed problem.

So, you've got to be really careful about that. In a perennial system it's not normally as big of an issue. We can get some nice perennial plants, we want them there year after year after year, and we're going to manage them for that.

why are some winter cover crops easier to manage?

So there are some specifically brassicas or legumes that don't survive a hard winter. Some of those, such as an oil seed radish, are over 90% water. So, they die over the winter and in the spring there's just nothing there. You don’t have to till it in. You can go into your field and plant.

I work with ornamental bulb farms and they'll plant oil seed radish after they lift their bulbs to sell. They plant the oil seed radish in the fall and then they can go back in the spring and replant the bulbs without any management. We can use oil seed radish for “bio till.” They'll actually till the soil up with their root systems. So those we don't have to do much.

Or oats are one of my favorites for winter kills. It's a wonderful cover crop. We can plant it in most any soil type, as long as we plant it at the right time.  It's going to grow and then doesn't survive our Michigan winters. And when you go back in the spring, it's dead. Some of the plant may still be sticking up out of the ground and you may have to lightly knock it down. But you should be able to go in and plant in it without tilling at all.

Listen to the entire, hour long episode below.

Susan Poizner

Director, OrchardPeople.com Fruit Tree Care Education

Learn more about Susan on the about us page.