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Repellent Companion Plants

Many plants will naturally control pests in your garden. It is possible to cover the scent of their favorite foods, use plants or extracts to annoy or kill pests, or even create physical barriers to keep insects away from your plants. You might even want to try using some plants that are said to repel vertebrate pests such as gophers, deer, and rabbits.

Scent Barriers

The chemical compounds created by strong-smelling plants can discourage most pests. Bold perfumy or lemony frangeces can be found in such plants as mints, thyme, lemon balm, and lemon geranium. Since many herbs produce these compounds, they become natural choices for companion plants. Mixing them in amongst pest-prone plants may just keep the pests guessing where the food is.

Garlic has long been touted as a companion plant for plants that are prone to pests such as aphids and mosquitoes. But, it will also deter their natural enemies, the lacewings and ladybugs. There is some evidence to show that there may be some fungicidal and bactericidal properties to garlic which might help protect tomatoes and potatoes from blights. A garlic oil extract (Soak 3 ounces of minced garlic in 2 teaspoons of mineral oil for 24 hours then strain and add 1 pint of water and 1 teaspoon of liquid soap. Use at the rate of 1 to 2 tablespoons of the mixture in 1 pint of water and spray on the pests.) may be even more effective, but beware - it will kill the good bugs, too.

Plant Fences

Since many of the destructive flying insects just ride the breezes, alighting wherever they find a suitable plant, you may be able to keep them from your plants by putting up a barrier of plants that they don't like. Block the prevailing wind with a fence, trellis, hedge, or screen. Use tall plants such as sunflowers or deciduous shrubs to screen your garden throughout the growing season. Planting evergreen shrubs and trees can block the wind year-round. These types of leafy barriers can also serve as shelter for beneficial insects.

Vertebrate Controls

It has been said that people are the only animals who enjoy spicy or strongly aromatic foods. If that is the case, it should be possible to discourage other kinds of creatures from turning your garden into a smorgasbörd. Sound your garden with boldly scented or spicy herbs and vegetables for an edging that you will enjoy, but animals won't.
Folklore and other sources have claimed that certain plants are especially good for repelling deer, rabbits, moles and similar nuisances. Planting the seeds of castor beans at 5 or 6 feet intervals around your garden is said to keep out moles and deer. Again, there needs to be a warning attached to this. Castor is toxic to children, and eating a few of the seeds has been known to be fatal. The mole plant (Euphorbia lathyrus) is said to repel mice, gophers, and moles. Some gardeners claim that you can annoy gophers by planting it next to their holes or by spacing plants every 5 feet around the garden as a barrier.

Unfortunately, with both of these, there is nothing that will necessarily stop the pest from just going around these unpleasant plants. Only a fence (8 feet high for deer, 2 feet high and 6 inches deep for rabbits, and 36 inches deep for gophers) will be more of a guarantee.


Marigolds and Nematodes

Having problems with nematodes? You might want to try marigolds. In addition to being beautiful plants, many gardeners swear by their power to repel all kinds of pests.

So far, scientists have only been able to show that marigolds can affect root knot nematodes and root lesion nematodes - microscopic soil-dwelling pests. The roots, and produce compounds called thiophenes. Studies have been inconclusive as to whether these chemical compounds kill the nematodes chemically or whether the nematodes get trapped by the roots of the marigold where the thiophenes keep them from reproducing.

However they work, you can use marigolds to clear nematodes out of the soil before or after planting susceptible crops. Any cultivar of American or French marigold will work. There is a 7-foot tall variety called 'Nemakill'. For best results, space the plants evenly over the bed. If you clear out your bed each fall, you can shop up the tall stems and turn everything under at the end of the season. As marigolds decay, they'll kill anything you plant. But by spring, the soil is safe for planting again. For this reason, I personally would not "plow" them under in a bed where you keep perennials. But, they should be safe to add to compost heaps.


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