Science and the gardener

Jill Severn

JILL SEVERN & GEORGE WALTER

Slugs and snails, gardens and birds

JILL SEVERN'S GARDENING COLUMN

Dishing on dirt

A couple of weeks ago, George Walter and I teamed up on a column about the damage slugs do in gardens, and their value as food for birds. We quickly discovered that slugs are a hot topic that elicits plenty of opinions.

One reader swears by her crunched up eggshells as a slug deterrent, even though we linked to an article in The Guardian that reported on research by the Royal Horticultural Society (RHS). It concluded that eggshells (and several other remedies) don’t help. Another reader is sticking with beer (untested by the research), and yet another is determined to keep using the poisonous product we recommended against, but hides the bait and the dead slugs from birds and other animals under a pot.

Our favorite was the reader who scooped slugs into a jar and traded them to a neighbor for duck eggs. This brought back memories of having happy ducks roaming the yard with slug slime hanging from their bills. For ducks, slugs are fine dining. For people, duck eggs are.

Aside from being entertaining, that conversation alerted me to a conflict between science and experience. If a gardener uses eggshells and observes that they deter slugs, I needed to ask more questions.

So I went to the RHS website to find out how big the trials of various methods of slug control were, how long the studies lasted and whether they’ve been replicated. Were they sure about the eggshells? It turned out it was a brief, small project that ended with intentions for further study. This is not, to say the least, settled science. I should have checked that out sooner. So should The Guardian‘s reporter.

Eggshells came up in an even less science-informed venue this week: Facebook. When a gardener asked what she should add to her soil to perk up her plants, adding eggshells to the soil was the first suggestion.

Tea bags were also recommended, but only if no sugar had been put in the tea.

Banana water got multiple mentions. It’s made by putting banana peels in a big jar of water, letting it sit in the sun until bubbles appear, and then pouring it on. A caveat: We are advised not to put the banana peels in our gardens because they will attract animals. (Also, banana peels are known to attract comedy.) There are a remarkable number of websites and YouTube videos about banana water. I wonder if someone started this trend as a prank.

Epsom salts are also a popular folk recommendation, as are coffee grounds, coconut water and lime. At first, this being Facebook, I wondered if the contributor meant lime as in Margueritas; on second thought, perhaps they meant ground limestone.

A final Facebook expert advises us to season our soil with pepper, sage, rosemary and garlic.

Not surprisingly, more sensible websites urge caution about some of these ideas.

The final item on the Facebook suggestion list was bunny poop. That’s a clever and appealing name for rabbit manure, and whoever coined the term may have a promising career in marketing. But it’s also a solid idea: the Easter Bunny and all his relations do indeed poop out a well-balanced plant food/soil amendment that comes in tidy little pellets.

The complexities of soil chemistry, fertility, and plant nutrition – not to mention slug control – are often confounding to both new and experienced gardeners. The proliferation of low-quality science and fanciful online trends can deepen the confusion. The gardener’s challenge is to question authority – even our own – and to be savvy critics of all we see, hear and read.

Here’s a beginner’s guide to the basic, settled science about garden soil and what it needs. But beyond this, we’re on our own to conduct our own experiments, evaluate causes and effects, and protect our plants from slugs.

Jill Severn writes from her home in Olympia, where she grows vegetables, flowers, and a small flock of chickens. She loves conversation among gardeners. Start one by emailing her at  jill@theJOLTnews.com