Garden Variety: Old wives’ tales have no place in the garden

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Old wives' tales led people to think eggshells could be used in the garden to deter slugs, cure blossom end rot, and provide calcium to plants despite research discrediting those supposed benefits.

Old wives’ tales, myths and misconceptions perpetuate in the garden world thanks to self-proclaimed experts, clever marketers, and well-meaning friends, family and neighbors. Sorting out bad information from good is a challenge at times, especially with regional and seasonal variations. Start this year off right by following these tips to get the most reliable information for gardening in the Lawrence area and avoiding the top gardening myths.

How do you know whom to trust? The best resources for lawn, landscape, garden and houseplant care are research- and education-based. In Lawrence, start with Kansas State University Research and Extension. Neighboring states’ land-grant institutions may provide additional resources and support, including the University of Missouri, University of Nebraska Iowa State University. Other universities are reliable, but the information may be less applicable here because of differences in soil type, seasons, weather, etc.

Beyond that, look for information that has science to support it. If the author or speaker only shares anecdotal information, talks about the practice being handed down through generations or tries to sell you a product, use extra caution.

Here are some of the top gardening myths and advice to avoid:

• Putting gravel in the bottom of a flower pot — The story goes that when potting up a houseplant or other plant in a container, you should put a layer of gravel, rocks, broken pottery, etc. in the bottom of the pot before adding potting soil. The gravel is said to improve drainage.

You can disprove this yourself by placing a sponge over a bed of gravel. Pour water onto the sponge. You will see that the water moves through the sponge until it hits the gravel, then stops. If you add more water until the sponge is saturated, excess water will move into the gravel but the sponge remains saturated. You are essentially raising the water table and reducing the volume of soil in the container.

Skip the gravel and fill flower pots only with high quality potting mix instead.

• Using eggshells in the garden to deter slugs, cure blossom end rot, and provide calcium to plants – There is a lot of advice floating around about all the wonderful things eggshells can do for plants and pest control. Research disproves all of them.

Avoid using eggshells in the garden.

• Use landscape fabric/weed barrier cloth for a weed-free landscape or garden. Landscape fabric is a black mesh product typically sold on a roll that can be laid out and stapled to the ground when planting. Mulch over the fabric to cover it, and the garden will be weed-free for years.

Landscape fabric works for a very short time. Then, as the mulch that covers it breaks down, weeds will start growing on top of it. Some weeds will also grow laterally under the cloth and develop extensive root systems before emerging on the edges.

The bigger downside of landscape fabric is that it prevents water movement into the soil and blocks the natural exchange of air from soil to the atmosphere. There are millions of beneficial fungi, bacteria and other microorganisms living in the soil that need water and air.

Use mulch instead. A four inch layer of mulch works as well as landscape fabric and improves soil rather than diminishing it.

• Adding sand to clay soil to improve drainage – The idea is that sand drains better than clay, so mixing the two together will create a happy medium.

The difficulty with this advice is the wide variability in soil types, actual clay content of soils and varying particle sizes of sand. Research supporting or disproving this advice is lacking, especially with northeast Kansas soils. Besides the beneficial claims, there are also anecdotal claims that the practice will worsen drainage instead of improving it.

In this case, adding sand might work for your soil or it might make things worse. Adding organic matter is a safer bet.

• Poinsettias and rhubarb are poisonous – Poinsettias, the popular holiday indoor plant, and rhubarb, an old-time garden plant are both reported to be poisonous to humans and pets if ingested.

Poinsettias have a milky white sap that can cause some skin irritation. They have very low toxicity to humans or pets when ingested. The Pet Poison Helpline reports that dogs and cats may vomit or drool after ingesting poinsettia, but the concern is greatly exaggerated.

Rhubarb contains oxalic acid, a substance produced by many plants which is poisonous in high quantities. The old wives’ tale with rhubarb is that the stems are safe to eat but not the leaves because they contain higher amounts of oxalic acid.

Research on the lethal dose of oxalic acid shows some variability, but an average adult would likely have to eat 10+ pounds of rhubarb leaves to be poisoned. Spinach leaves contain about twice as much oxalic acid as rhubarb leaves and chives contain about three times as much oxalic acid as rhubarb.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.


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