(illustrated version)

Making Merry in the Mulch: of Toads and Toad Lilies

June 4, 2001

For years now I've been recommending the use of fall leaves as a mulch. I'm in great company in this (as any of you who have heard David Tomlinson speak will know), and I don't withdraw the recommendation, but I thought I'd qualify it just a bit.

Often people will ask me if I rake up the leaves in the spring. I don't. I do sometimes help a few struggling tulip shoots push through the mulch (most of the leaves in my neighborhood are maples, which make a tough mat when damp) but I leave the leaves in place for the earthworms to munch upon. Usually by the end of June the leaves have been turned into worm castings, enriching the soil.

This year, however, I found an exception I must make to this rule. I had been wondering for some years about a healthy patch of Toad Lilies (Tricyrtis hirta) which disappeared without a trace over one winter. The previous fall I had given the patch a topdressing of both compost and leaves.

This spring another patch of toad lilies seemed about to go the same way. All the others were up and growing and there had been no sign from under the leaves of these. As I value the charming little flowers on arched stems of Tricyrtis quite highly in my fall garden, I decided further investigation was in order.

What I found on lifting the leaves was what any hosta grower could have told me. A symposium of slugs was feasting on the tender growing tips of the toad lilies, chomping them down as fast as they could grow up. I hastily removed the leaves, applied a very few slug bait pellets, and now a few weeks later the patch has recovered nicely.

I hadn't quite learned my lesson, though! Normally I plant lilies in the fall, much the best way, as their roots need time to develop. However a very advantageous price in a local garden centre tempted me into spring planting. This was during a very dry, hot spell in late April/early May, so I carefully mulched the spots where the bulbs went in.

In late May only a few of the lilies were showing. Once again, inspection revealed squadrons of slugs feasting on the tender tops of the lilies. Again, removal of mulch and a few bait pellets saved the plants.

I thought about my experiences for a little while and realized what is happening. Early in spring, when tulips, crocuses, and fall-planted lilies are coming up, the soil is cold and the slugs, well, sluggish! The tenderest shoots shoot by the danger zone and are quickly out in dry air. But plants that start growth late, especially those spring planted or those in the shadiest parts of the garden, pass out of the soil into the mulch when warm rains have stirred the slugs into action.

Some plants, like daffodils, rhubarbs, snowdrops, and others, have toxic substances in their shoots to discourage grazers. But many plants in the lily family, such as hostas, lilies, and toad lilies seem to be very tasty indeed, so if their growth is delayed, watch out.

So, in the future, I'll rake the leaf mulch off the toad lilies and any spring planted lilies just long enough for the plants to get a few inches tall. After that their stems toughen up and are less attractive.

The very best way to reduce problems with slugs of course is to encourage a lively community of toads. Unfortunately, in my neighborhood of downtown Toronto there are too few breeding habitats (lakes, marshes, or large ponds) to sustain toads. Proposals have been made to establish runoff water holding areas in several city parks nearby; so far none of these has progressed the next step to creating spring ponds (those with at least 30-60 cm of water from April through June) where toads could breed. Even my backyard pond, 1 m deep and 2 m wide, is not quite big enough for toads, though I keep hoping. I'm pinning my hopes on the parks, but am not holding my breath.

Lacking toads, what are we gardeners to do? There's always drowning the slugs in beer, or pouring on salt, but an old, toxic solution (slug bait) has just gotten environmentally friendlier.

Did you know about the new slug baits? The older ones contained compounds (metaldehyde or methiocarb) which were toxic to other animals as well as slugs. This meant you had to be careful to cover up the pellets after applying them, to keep birds, pets, and babies from eating them.

The new baits (available in such brands as Safer's Slug Bait, Sluggo, Multiguard, etc) contain various iron compounds such as ferric phosphate. These compounds tend not to be absorbed well by the stomach and intestines of mammals, so they are much less toxic if eaten. They don't kill the slugs as quickly as the older more toxic baits, but the slugs stop feeding soon after taking the bait, so no more damage is done to your garden.

Copyright 2001 by Clement Kent, c l e m e n t @ g o d e l . n e t

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