What’s the best way to eliminate Japanese beetles? Photo by Lela Martin

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Yes, April showers do bring May flowers, though tulips tend to bloom in April. Photo by Lela Martin

Many gardeners rely on a proverb, an almanac or their grandmothers for gardening advice, while Master Gardeners are trained to convey information that is research-based.

Here are a few adages with a little bit of scientific discussion to clarify the level of their validity:

April showers bring May flowers

This saying can be traced back to English poet Thomas Tusser, who wrote in the 1500s, “Sweet April showers do spring May Flowers.” In England, the jet stream lifts northward at the start of spring, bringing weather swings and more rain. The jet stream in the U.S. also moves north in spring.

In Central Virginia, April and May are tied for second as the rainiest month after August. Additionally, increasing air temperatures by about 10°F during April, combined with warming soil temperatures, do indeed stimulate the budding and blooming of flowering plants.

One bad apple can spoil the whole barrel

Is this how you remember the saying? If you grew up hearing The Osmonds sing “One Bad Apple” by George Jackson, you might think the saying is “one bad apple don’t spoil the whole bunch, girl.” So, which is it?

In fruits such as apples, tomatoes and bananas, ethylene gas is produced internally to stimulate ripening. Ethylene triggers a complex process that ends in rotting, with more ethylene being released into the surrounding air. This spurs the ripening of nearby fruit, setting off a chain reaction that, with time, spoils it all.

Adding sugar to the soil will make your tomatoes taste sweeter

Tomatoes do not get their sweetness from the soil. Instead, sweetness is determined by the variety of tomato, as well as plant photosynthesis. Typically, the sweetest are cherry and plum tomatoes.

Ants help peony flowers open

Peony buds often have ants on them because ants are attracted to the sugary secretions produced by the plant. While ants do nothing to contribute to the flower opening, they help keep away other insect pests in exchange for peony nectar.

Eliminate white grubs this year, no Japanese beetles next year

The larval form of the Japanese beetle is a white grub in the soil. Treating for grubs may reduce the number of grubs in your lawn. Unfortunately, Japanese beetles can fly 10 to 15 miles, so they will come from other yards.

Furthermore, the beetles release an aggregation pheromone that tells other Japanese beetles where to find food. Because hanging traps contain this pheromone, they just attract Japanese beetles.

The best control is to go out in early morning and pluck the beetles feeding on your plants, dropping them in a bucket of soapy water.

Nothing grows under a walnut tree

The black walnut (Juglans nigra) produces a chemical called juglone that remains in the soil beneath it and destroys or deters plants from competing with it.

This is called allelopathy. Some other plants, including fescue grass, have lesser degrees of allelopathy.

Plants most susceptible to the black walnut’s toxicity include birch, pine, azaleas and plants in the nightshade family, such as tomatoes and potatoes. Some native plants that tolerate juglone and can grow under black walnuts include asters, ferns and Virginia bluebells.

Abundance of acorns means a bad winter

This has not been proven. When you see a mast crop (large number) of acorns, it simply means that the oak tree had a good growing season.

Many proverbs have to do with when to plant or harvest. Phenology (not to be confused with phrenology) is the study of cyclic and seasonal natural phenomena, especially how climate is related to plant and animal life.

Plant potatoes (or beans) on Good Friday

First, the date of Good Friday changes each year. Second, the weather on Good Friday is variable from year to year.

A better rule of thumb is to plant potatoes (or beans) once the risk of frost has passed. In Central Virginia’s Zone 7, the last frost date typically falls between the end of March and mid-April.

Corn should be knee-high by the Fourth of July

This is one my mom, who grew up on a Kentucky farm, used to say. Years ago, if corn plants were knee-high in early July, they would be growing at a good rate.

However, with advances in agricultural technology and plant genetics, in most years corn should be waist-high by July Fourth.

The earlier saying morphed in 1942 to corn will grow “as high as an elephant’s eye.” This comes from the lyrics of “Oh, What a Beautiful Morning” from the musical Oklahoma!

Sweet corn plants can reach six to eight feet or more in height by late July or August. Chicago’s Lincoln Park Zoo says an elephant’s eye is about six or seven feet high. Maybe Oscar Hammerstein II knew something about farming!

You should garden by the moon

The basic idea behind this belief is that the moon’s phases affect plant growth. According to this thinking, it’s considered best to plant crops that grow underground (such as potatoes and carrots) on the days during the dark of the moon or its waning (the time between the full and new moon).

Conversely, crops that produce edibles above ground (such as beans and broccoli) supposedly should be planted on days during the light of the moon or its waxing (the time between the new and full moon).

Additionally, as the moon’s gravitational pull causes tides to rise and fall, the theory is that it also affects moisture in the soil.

While gardening by the moon may not be lunacy, it has not been supported by research.

Lela Martin is a Master Gardener with the Chesterfield County office of the Virginia Cooperative Extension.