Saturday, June 2, 2012

Of dahlias, snails, slugs and eggshells

Snails think dahlias make a lovely lunch.
     Once again, with newly planted dahlias just up or due to emerge from the ground, it's time to find ways to combat those kings of the dahlia pests, hungry slugs and snails.
     With a reservoir nearby and ivy all along one property border, our garden's a sitting duck for these wretched mollusks. Last year, I had good luck planting my dahlias in pots and topping them up with a good, thick layer of coarsely crushed eggshells.

     Sad to say, a gardening buddy took note and, as I do, saved eggshells all winter to protect his garden against snails and slugs. He set out a nice row of cabbages and covered the ground around it with a hefty layer of eggshells. The next morning, he went out to gaze proudly at his garden and found that all but three of his cabbages had been reduced to stubs.

Eggshell topping kept this pot of dahlias slug-free.
     The problem, he realized, was that he'd prepared the ground for planting with a nice compost mulch. The slugs had probably been snoozing in the mulch, just waiting for him to infuse the area with breakfast.

     The job when you're growing dahlias,  then, is to try to make sure that your composted soil and mulch are slug-free at planting time: no easy task, since even if you eliminate any slugs from the composter, there's a likelihood that there can be eggs that will hatch later and produce tiny, but voracious, junior slugs and snails.

     One inventive gardener we know puts tubs of his compost into the barbecue and heats them to kill any lurking slugs, snails or eggs. It works well, but don't try using the oven; the smell is appalling. (My mother once tried that to sterilize potting soil for her petunias.) It's also pretty labor-intensive for a large garden area.  Your best bet is to plant in rich soil but wait to add mulch until your dahlia plants have gained at least half their height and their stems have begun to harden off. Avoid over-watering. And a barrier of eggshells around your dahlias, and especially between their bed and any ground covers or other haven for slugs and snails will help too.

1 comment:

Mary St George said...

Snails will not only cross egg shells, but actually eat small quantities of the egg shell. They need sources of calcium to grow the shells on their backs. Fresh untreated wood ash is a better deterrent, because it is mildly caustic, however it needs replenishing after rain. I have been interested to read recently that diluted ammonia can be sprayed on slugs and snails while they are active on damp foliage, and can be a useful form of control when used in this way. The ammonia spray also gives the plants a foliar feed of nitrogen. I have yet to experiment with this myself. It is considered to be an organic method of control, apparently, but anyone following a certified organic programme would need to check with their organic growers organisation whether it was acceptable to them, too.

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