Slug Proof Plants – what don’t they eat?
By Andy McIndoe •
Slug proof plants…..I bet that got your attention.
Slugs and snails are the bane of many a gardener's life; they munch their way through precious new shoots, devour seedlings and cause devastation to many of your favourite plants. But the Royal Horticultural Society (RHS) has just announced that they'll no longer class slugs as pests, but as an important part of the garden ecosystem.
Some plants are just slug magnets: hostas for example. You may try to protect them with copper tape, grit, wheat bran, beer and hundreds of other magic repellents but those slimy little critters will probably reduce your precious funkia foliage to lace at some point in the season.
Slugs and snails have built a reputation on destruction and I don’t think I’ve ever done a Gardener’s Question Time without the question of slugs.
However there are plenty of plants that they do not eat; so the simple answer if they are a problem is to grow more subjects that are not on their menu.
In many cases the selection of slug-proof plants is common sense. If leaves and stems are felty, hairy, dusty or tough then they are less likely to be slug fodder. Silver foliage subjects like lavender, santolina, helichrysum and teucrium are rarely devastated by molluscs.
When you think about it these tend to have leaves that are aromatic and repellent too. The golden-leaved form Santolina ‘Lemon Fizz’ offers a lively alternative to the usual silver foliage.
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View courseAll Gardening coursesI’m not going to talk about shrubs because these are not usually slug and snail targets. Their woody stems are not appealing either to eat or climb over.
Perennials
When it comes to perennials keep the aromatic element in mind. Plants with oil-rich foliage are usually more resistant. Take herbaceous geraniums for example. Slugs and snails may hide beneath the leaves, but they do not eat them.
The early flowering Geranium phaeum even grows well in shady spots which slugs and snails love, but they will not feed on its leaves or flowers.
Herbs
Marjoram, Origanum vulgare and its various forms are totally slug resistant. On light, dry soils it often seeds prolifically but there is no denying its value as a drifter in the border as well as a culinary herb.
The golden-leaved form is particularly attractive early in the season when the leaves are fresh and bright and in late summer when the plants are in flower and the leaves change to soft gold.
Foxgloves
Foxgloves are poisonous, so they are left untouched by most voracious pests including deer and rabbits. The wild foxglove, Digitalis purpurea is a biennial, in other words it grows one year, then flowers, sets seed and dies the next.
However some foxgloves are short-lived perennials, Digitalis ferruginea for example. This is an even more desirable garden plant with its upright spikes of tightly-packed coppery flowers; you’ll love it but slugs and snails will hate it.
Euphorbias
Euphorbias, the spurges as they are commonly known, fall into the same category. Their stems and leaves contain a milky, irritant sap which gardeners should avoid getting on their skin. This makes them repellent to any pests.
Again deer and rabbit proof they are also slug-proof. The tall and architectural Euphorbia characias is a striking plant which will seed on sandy, well-drained soils. Plants live for a number of years, producing new stems from their woody bases each season.
This euphorbia is an evergreen perennial; more like a shrub in many ways. The lime green “flowers” at the tips of the stems are stunning in late winter and early spring.
Penstemons
Penstemons are similar in some ways in that they are evergreen and have woody stems. I’m not going to recommend these as slug proof however because slugs and snails seem to devour them in some gardens, so I am told.
However I will recommend the evergreen hellebores such as Helleborus x ericsmithii and Helleborus argutifolius. These have tough foliage and tough flowers carried above the foliage in large clusters. These seem to be unpalatable to molluscs and they are carried well out of harm’s way.
They also grow well in shade, so they will brave those haunts of our slippery enemies.
Pulmonarias
Here too pulmonarias, the lungworts resist attack whereas hostas will be devoured. Pulmonarias have the benefit of early flowers and attractively patterned leaves, sometimes spotted or overlaid with silver. The foliage can become rather tatty as the season progresses, but it rarely looks as unsightly in the garden as a slug-damaged hosta.
Seedums
For sunny positions in the garden sedums are invaluable for late summer colour and their strong, bold plant forms. Sedum spectabile and its cultivars are the best known and most widely grown.
Occasionally slugs may have a nibble at the fleshy growth buds clustered on the soil in early spring, but they don’t seem to do too much damage as the stems grow. If damage does occur, surround the crown of the plant with coarse grit which the slugs won’t like to cross and the plant will enjoy the drier soil surface.
In most gardens the stems and faded flowerheads, which turn deep brown, remain attractive into winter. In others they seem to collapse as the stems outgrow their strength. This is a particular problem in late winter.
To prevent this cut back the stems by one third to a half in late spring. They will then branch, but grow shorter and remain upright. The flowerheads will be smaller but the overall effect should be more pleasing.
Aquilegia
One of our favourite cottage-garden plants, the aquilegia or columbine is also a good slug-proof subject. There are many forms and they do tend to hybridise and seed around the garden; all a part of their charm.
The varieties with larger outer petals and long spurs are some of the showiest; Look out for the ‘State’ series. Aquilegias are good “drifters”: plants you can tuck in between other perennials and shrubs where their long flower stems and nodding blooms will add light height to the planting.
Agastache
As I said anything with aromatic foliage is always a good choice as a slug resistant plant. Agastache foeniculum, the giant hyssop, is becoming more and more popular as a border perennial and for use with grasses in prairie schemes.
There are a number of excellent varieties with larger and showier flowers than the species. Their appeal is their attraction of bees, butterflies and pollinators; the bonus is their unattractiveness to slugs and snails.
Other perennials I’ve found to be pretty mollusc resistant include: Knautia, eryngium and nepeta.
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NEW 2022 RHS Level 2 syllabus - everything you need to know to help you pass the RHS Level 2 Certificate in the Principles of Plant Growth and Development.
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