In the past I have sprayed my hosta with an ammonia solution in the early spring while the hosta were just emerging. My hosta is now 4 to 6 inches high and just beginning to leaf. Can I go ahead and spray them or is too late?
Thank-you for contacting Toronto Master Gardeners with your question.
Unfortunately, hostas and slugs are perennial partners in our Toronto gardens. We have handled this issue in several queries on our website. I am including a previously published answer as I believe it will give you as comprehensive an answer as I could. The one thing I would stress from personal experience is that while no hosta is totally immune to slug predation, the “slug resistant” varieties now available, with their thicker, corrugated leaves, do seem to attract fewer of these pests.
The Toronto Master Gardeners do not recommend chemical control for any pests. The Ontario ban on use of pesticides for cosmetic purposes included a ban on home remedies, like use of soap and diluted ammonia outdoors. Gary Westlake of the Peterborough and area Master Gardeners, in Gardeners Get an Earth Day Present from the Province clearly explains this.
It may be challenging to find slug eggs, but if you clean up your yard, get rid of organic matter and wood and any other items that could provide shelter for the slugs, you’re off to a good start. The eggs may be on the surface of the soil and are often covered by debris or leaves. Unfortunately, as you won’t be able to find ALL the slug eggs, you may have a number of adult slugs invade your garden.
The best way to get rid of slugs is to hand-pick them in the early evening, about 2 hours after sunset, as the critters are more active at night. Go out with your flashlight, and examine the bases of pants, backs of leaves and between the rows of your vegetable garden. You can use a spoon to loosen the slugs from the plant, then put them in a pail of soapy water. Other methods, e.g., trapping them and spreading diatomaceous earth in areas they like to hide (this acts as a barrier as the particles are scratchy), may also be effective. See the Government of Canada’s article, Slugs and snails.
There are also strategies you can use to make your garden less attractive to slugs. The Toronto Master Gardeners and City of Toronto collaborated to prepare the fact sheet https://torontomastergardeners.ca/wp-content/uploads/2012/07/Integrated-Pest-Management.pdf. Much of the information in this article is relevant to your slug problem.
- Choose plants that are resistant to slugs – e.g., see All About Slugs’ Slug and snail resistant plants. And ask your local nursery for plants that are less likely to be attacked by slugs. For example, while no host is slug-proof, there are some varieties that are more resilient to slugs (in particular the varieties with blue leaves that are thick and puckered).
- Water the garden less frequently and more deeply, and try not to water late in the day – morning is best (slugs are less active then)
- Slugs gather under mulch and other debris, and among weeds, so keep the garden area as tidy as possible.
And examine your plants often for signs of damage from slugs – look at the whole plant, from top to bottom, and both sides of leaves. If slugs have started to appear – take out your flashlight and go hunting!