Companion planting (planting certain plants or flowers near each other to complement each other's growth and reduce weeds and pests) has been practiced for a long time. Until recently, this planting technique lacked the scientific studies to show its benefits.
Now, more scientists around the country and around the world are experimenting with companion plants, and many of their findings are documented in a book published last year by Jessica Walliser called “Plant Partners.”
Science-based planting strategies
One of the interplanting strategies scientists have studied involves arranging plants for nutrient sharing.
Particular combinations that work well include plants that release nitrogen into the soil as they grow and plants that absorb it.
Legumes such as peas “fix” nitrogen, or turn it into a form that other plants can use in the soil. That nitrogen is beneficial for leafy vegetables that thrive with high levels of nitrogen, such as lettuce, kale and Swiss chard. These plants do well when planted closely together in gardens or raised beds.
Another way to study successful companion planting is to look at the root depth of the plants – for example, lettuce has very shallow roots, while carrot roots grow very deep.
These two types of vegetables get the nutrients they need from different layers of the soil, so they won't compete with each other if planted close together in the garden.
Another plant combination technique that has been used for decades in home gardens has to do with pest control.
Certain vegetable plants give off scents that attract pests, who then take up residence on the plant, lay eggs, which develop into larvae and destroy the plant.
These plants are sometimes called “plant traps.” Studies have shown that planting “plant trap” crops, such as Hubbard squash, can attract pests that bore into squash vines and keep them away from other squash plants. To prevent these pests from infesting your entire garden, try to plant squash in a separate garden space.
Other scientifically tested plant combinations use aromatic compounds to scare away garden pests, such as planting nasturtiums next to zucchinis or summer squash.
Nasturtium flowers give off a scent that insects find attractive and hides your pumpkin plants. If garden pests can't find your pumpkin plants, they will lay fewer eggs and fewer larvae will hatch, minimizing the risk to them.
This scent-masking technique also works well if you combine basil and tomato plants: try planting some basil that gives off a scent that confuses the tomato wasps to see if that reduces egg production.
Questions about blueberry revival
Q: I was pruning dead branches from my blueberry plants and noticed black spots on one of the trunks. They look like spider mite spots, but they are black instead of white. What's going on with the blueberries? How can I save the plant? – Karen, Elmore
A: Because we've had a lot of rain this spring, there may be a fungal disease on the leaves, so it's a good idea to keep the plant clean by pruning away any dead branches.
You can also spray it with neem oil, which is a fairly harmless fungicide.
This is also a good time to fertilize your blueberries, especially if you need to lower the soil pH level, as fertilization will help alleviate the problem and make the plants stronger.
Next year, prune your blueberry plants a little more to encourage new growth, which will encourage more vibrancy, reduce dead shoots, and encourage larger, fuller plants.
Asparagus: To Fern or Not to Fern
Q: Two years ago I wrote you about the woodchucks that were devouring our asparagus and whether it would still grow last summer. Good news – it did! But last year we were unable to contain an infestation of asparagus beetles and their hungry larvae. This is our second summer without a good fern. This spring the asparagus is growing but the stems are very thin. Should I harvest the thin roots or let it fern from the beginning? – Barry, Lipton
A: A good rule of thumb for asparagus stalks is that if they are thinner than the diameter of a pencil, they should be left alone until they become ferned.
Asparagus has been heavily damaged by asparagus beetles and woodchucks so it may be best to leave it alone.
We also recommend feeding your asparagus with compost now, placing it all around the plant and making sure the soil drains well.
These adjustments will hopefully improve plant condition for next season and reduce asparagus pests.
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