If you are squeamish, don’t read on. This will not be pleasant.
I tell myself that Cornwall is a bad area for slugs, that mild winters mean they are active all winter, breeding all year round. Our often wet summers mean we don’t get prolonged dry spells to reduce their numbers. I tell myself that anyone gardening in a worse place for slugs would simply give up. I know they are pest number one for most of us.
I have Dahlias in a number of places in the garden and the best of them are now about two feet tall. The worst of them are barely two inches tall and consist of chewed off leafless stems. I have one prominent bed with Dahlias planted in the middle of it. It is still largely bare ground, which is pretty disappointing half way through June. The difference is entirely down to slugs. According to one website they consume up to 40 times their own weight in a day. I’m not sure I believe that but they certainly do a huge amount of damage.
Generally when plants are relentlessly targeted by slugs, I roll over and give up the fight pretty readily. I am very reluctant to use even the supposedly wildlife friendly slug pellets as I know we have hedgehogs around and want to do all I can to encourage them. I’m not sure that giving up on most slug vulnerable plants, then doggedly carrying on growing one of the most susceptible makes sense, but it’s the course I’m set upon and I’m not ready to give up yet.
My main control method is simple. I venture out when there’s just about enough light left to see by, around 9.30 at present, and go round the garden checking on all the plants that get attacked, dispatching the slimy assassins by cutting them in half with secateurs. Over the last three evenings I have killed over 500, almost all the brown version of black slugs, quite big things, around 2 inches long. On one foot high Dahlia there were 36 of them.
The difference between the area where the Dahlias are growing well and the rest is that there is nowhere for them to hide during the day. Mostly they hide under nearby plants, within 3 or 4 feet of the thing they’re targeting in most cases, and they are most fond of Primulas and Foxgloves in my garden, they being the things with large, low, spreading leaf canopies.
My supplementary control method then is to go round during the day, checking for slugs in their most likely hiding places and killing them. As well as providing them with cover, it provides me with likely places to look.
When Dahlias are first emerging, a single slug can remove all the above ground growth in a single night. If it keeps coming back, the plant simply never grows away. Once the plant is a few inches tall, it can usually grow faster than the slugs can eat it.
Does my method work? I think it does, but I think what I fail to do is to go in as soon as the first Dahlias show with a full on assault. That’s the time to be meticulous and seek them out in their bunkers. Instead I tend to grumble and not do much, building up slowly to being thorough. It needs to be the other way about, thorough to begin with, then relax a bit as the plants grow away.
It may be that if there is too much nearby cover, it just isn’t possible to grow Dahlias well. Perhaps in those areas I grow something else or lift the Dahlias, start them in pots under cover and plant them out when they are big enough to withstand some damage.