Adding a few simple companion crops (or "cover crops") to your soil-based grow room can benefit your plants in so many ways.
Companion crops are known to:
- Slow soil erosion.
- Improve the health of your soil
- Enhance your plants' water availability
- Control weeds and pests
- Increase root production
- Increase your overall yield
How? By sewing a cover crop into the soil of your main crop.
And in this article we'll explain how companion crops will help the quality of your plants, and which are best for your plants.
So let's get started!
Why plant cover crops?
Companion crops have benefits for your plants on the front and back end of your grow.
And they don't just help plants thrive and improve harvests, but they improve your soil going forward.
In fact, here's three big impacts companion crops will make to your grow:
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Increased Yield & Flavor: Cover crops do this by improving soil fertility, water retention, and reducing soil compaction.
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Pest & Weed Control: Cover crops help by providing competition for resources and releasing chemicals that deter pests and weeds.
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Soil Health: Cover crops improve soil by adding organic matter and nutrients to the soil, reducing soil erosion and runoff, and improving soil structure and biodiversity.
But for companion crops to have those impacts, you need to find the right crop for the job.
What companion crops should I plant?
You can tell a lot about your plants by the way they look, so identify what your plants need before you go sewing cover crops.
Here's four types of companion crops you can use depending on what your plants need:
1. Nutrient Miners/Scavengers
When your plants are looking a little yellow, chances are they need some extra nitrogen. That means you'll need something to scavenge for nutrients.
If that’s the case, grains like rye and wheat will help in good root growth because they are great at scavenging for nitrogen through your soil. But other plants that help include:
- Clover
- Peas
- Beans & legumes
2. Weed Suppressors
If your plants are starting to brown but weeds are popping up, then weeds are taking the nutrients your plants need. So you need a weed-suppressing crop.
Buckwheat and mustard are great for suppressing weeds and killing them before they can affect your grow. But you can also use these other plants to reduce weed growth:
- Sunflowers (this also attracts pollinators!)
- Oats
- Rye
- Hairy Vetch
3. Pest Deterrents
There's two things pests hate: odors and toxic plants. So if you're having trouble with pests you can keep them at bay by using flowers like marigolds and borage to repel pests.
But other plants and flowers repel pests, too, including:
- Nasturtiums
- Garlic
- Sage
- Dill
4. Soil Improvers
If your soil's compacted or deteriorating, cover crops can help break it up and keep it from eroding. Plants like radishes and ryegrass help break up soil to introduce more water and nutrients to keep soil loose for your plants.
And other plants that will improve your soil as they grow include:
- Sweet Alyssum
- Sunflowers
- Phacelia
And this is just a small sample of the companion crops that will help your plants.
But you have to be strategic about sewing cover crops. So here's what you'll need for success:
Utilizing your companion crops
Now that you know what kind of companion crops to plant, it’s time to see when you need to plant them. Because while cover crops help your grow, you don’t want them dying before they actually can:
- Start by determining the harvest time of your main crop.
- Then find out how long it takes for your cover crop to grow and begin to die.
- Based on these calculations you’ll want to plant your cover crop just in time so they’re growing with your plants and not against them.
For example, plants like rye should be planted early enough in the fall so that they don’t freeze in the winter (usually done for early-ripening plants). On the other hand, plants like cloves might need to be sewn a season or two ahead to ensure it grows nice and thick to help your longer-ripening plants.
Remember that when you’re using cover crops it’s important to use plants that will survive seasonal conditions. Again, you don’t want to plant rye in the dead of winter because it naturally grows well in the spring and summer.
At the same time, plants like cloves can be planted at nearly any time of year because of their resilience.
So choose the cover crops that work best with your growing schedule and the changing seasons.
So what happens to cover crops once I harvest?
Remember that after you’ve harvested your cash crop your companion crops will still grow.
These plants will provide your soil and future crops the same benefits your first cover crop harvest did, but how they get those nutrients can be all the difference when you’re working with a time limit.
The all-natural way of making “green manure” is to simply let your crop die off and decompose back into the earth. However, letting a crop naturally breakdown can take a long time.
Think about how long straw takes to break down in a field. It eventually will break down, but it’s going to take a while, and if you need to harvest fast you may not have the time to let Mother Nature do her work in your garden.
If this is the case your best option is to chop those cover crops and compost them. Doing this may leave a few nutrients behind (some things can only be released during the gradual breakdown of plant material), but this will make a majority of the nutrients in the cover crops available for use in your next grow.
Otherwise, you can allow your plants to naturally break down, till the soil, and you've got a super-charge soil bed ready for next season!
And there you have it, growers. Now check out your grow room and see where you can add a bit of color and a whole lot of growth.
Editor’s note: This post was originally published in October 2018. It has been updated for accuracy and comprehensiveness as of May 2023.