I have been battling with slugs for years. I never had them in my previous garden (all sand,) but I have oodles of them in my all clay garden. In fact, as I've amended the soil and made it more "loamy" the slugs have increased. They seem to like leaf mulches and thrive on the extra organic material.
In the battle of the slug, I've tried a multitude of organic remedies. This year, I am experimenting with the following: wood ashes, no mulch, and lava rocks.
In my main 2 annual beds, there is no mulch. ZERO mulch. This is a first for me and I can see the stress in my plants. They are not as robust and the soil dries out much quicker. I also added a thin layer of wood ashes last fall. I mixed it in in order to add nutrients to the soil and maybe wreak havoc on any slugs that were planning to overwinter. I have not seen any slugs, evidence of slugs, or slug damage in these two beds. I have, however, had lackluster growth and mass attacks of flea beetles. MASS attacks - many leading to the death of whole plants!
The other two beds are covered in mulches. One is covered in leaves and old garden debris - this bed may have slugs but the bed contains only raspberry plants and slugs have never dared climb their spikey bodies. Maybe they grow here and then migrate to the annual beds....
The other bed contains annuals, blueberries, and strawberries and is mulched half in pine needles/half bare soil. The bare half contains mostly onion family plants - chives, leaks, onions, garlic. I have not had slug damage in the bare soil area this year, but pulling back the pine needles to fertilize the blueberries revealed a slug extravaganza!
In addition, the strawberries near the blueberries were riddled with slug holes. Grrrrrrrrrrr! I thought the spikey pine needles would spear the slugs and make them rue the day they entered the garden. NO!
The ground under the pine straw is gloriously black and moist. I sometimes throw leaves, garden debris, cardboard, or kitchen scraps beneath the pine straw to decompose. It doesn't seem to harm the blueberries (never mind the center blueberry in the photo below - it is still repairing from 7 years of no pruning and the top portion is currently dying while "a new" bush forms from new canes.)
In fact, my blueberries (with the exception of the unpruned) are bigger, healthier, greener, and more loaded with berries than ever.
But there are slugs.
The slugs don't usually bother blueberries unless they are near the ground. So I didn't plan on killing them in the blueberry patch. In fact, I would guess they help quite a bit with decomposition of organic matter. But I do not want them eating all my strawberries.
So I devised this plan:
Strawberry season is pretty much over, but I do have one berry ripening in this patch. We shall see if it is protected from slugs or not! EVERY berry that has come out this year had at least one slug hole, so I would have expected this berry to be slug eaten as well. I will update in a few days.
Lava rock will make plant propagation more difficult, but I plan to pinch the runners anyway. I can always scoop them aside to dig and put in new plants. If they keep out slugs, it will be worth any/all extra work.
For other plants, slugs are still a challenge. You do not want to add wood ashes very often as they sweeten the soil (and my clay soil is already very alkalkine). Diatomaceous earth is ruined by water and kills all soft bodied insects indiscriminately. Mulches bring slugs.....but mulches maintain consistent moisture levels and provide organic material to feed growing plants. They also provide cover for other insects (beneficials included.)
Would it be prudent to mulch the annual beds, but ring each individual plant with lava rocks? If you till your garden, then rocks in the beds will be a challenge. I do not till, so I can always push them aside at the end of the season.
This year, I am committed to giving the no-mulch strategy a try. I want to see how it all turns out in the end. I'm also still trialing the lava rocks. We have a 1 strawberry test awaiting, and probably won't know the full extent of the benefits/issues until next July.
I will update this page accordingly:
**Update 1** The "one" strawberry made it and was eaten by a human being - rather than slugs.
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