How To Keep Alpine Plants Healthy Through Winter – Simple Steps to Prevent Waterlogging and Encourage Spring Growth

Alpines are tough plants, popular for being pretty, hardy, versatile, and low-maintenance. You may not think that this rugged group of plants needs winter protection, but neglect them at your own risk. The one thing that harms alpines in winter more than anything else is wetness.

Cold isn’t usually an issue over winter, but waterlogging during the colder months is an alpine plant’s nemesis. Stopping them from sitting wet for extended periods is key to overwintering alpine plants.

Thankfully, overwintering alpine plants isn’t too difficult. Either cover rock garden plants in situ with a cold frame, mini greenhouse (such as this at The Home Depot), or a cloche, and move potted ones indoors for winter. This prevents the roots or crown from rotting. Maintaining airflow is vital too, so fungal issues don’t build up and affect plants over winter.

The Hidden Danger of Winter Wet

Alpine plants naturally grow in tough conditions, often at high altitudes and in climates with intense sun, strong winds, and cold winters. Over the years, they have evolved to cope with these harsh environments.

For home gardens, this means alpines are drought-tolerant plants that can thrive in poorer soils. These low-maintenance plants need little watering or feeding once established, which has helped make them popular choices over the years.

With that in mind, overwintering alpine plants might sound unnecessary. However, one key difference between their natural habitats and most home gardens makes overwintering plants a balancing act – and one you need to get right.

It is not freezing temperatures that usually kill alpine plants in winter; it is waterlogging. Alpine plants usually grow at altitude and sit under an insulating layer of snow over winter. These winters are cold and dry. The snow protects them from icy winds and rain, and when it melts, the lean, rocky soil drains quickly.

This is not often the case in home gardens, where winters are usually wet and mild. Alpines aren’t protected from freezing rain, waterlogged soil, or repeated freezing and thawing, which can lift plants from the soil (known as frost heave). Long periods of sitting in cold, sodden soil can signal the demise of alpines.

The danger stems from the fact that alpines don’t absorb much moisture during winter. Jessica Mercer, Horticulturist at Plant Addicts, explains: ‘During wet winters, water fills the air spaces around the roots and deprives the roots of oxygen. Over time, the roots and crown can rot.’

‘Plants with hairy or woolly foliage (e.g. edelweiss, pussytoes, and partridge feather) trap more water near the crown and thus are more susceptible to crown rot,' she adds.

Such hairy or woolly plants, including spring-flowering alpine varieties of pulsatilla and saxifraga, won’t use all that extra water they store during winter and can quickly decay unless protected from the elements.

How to Protect Plants From Rot

Overwintering alpine plants will differ depending on where you grow them. Plants in a rock or crevice garden need protection in place, while potted plants in container gardens can be transferred to a sheltered spot.

Alpines in the Ground

Sensitive hairy and woolly foliage plants in rock, crevice, or gravel gardens can be covered for winter. This can be done with a cold frame, a garden cloche, glass panes, or plastic sheeting. The latter two need securing in place, and plastic sheets should be staked to keep them from blowing away.

‘When I lived in Seattle, where winters are mild but wet, I grew cold-hardy dryland plants in my rock garden under clear mini cloches all winter,’ claims Jessica Mercer. ‘These included sulfur buckwheat (Eriogonum umbellatum), beavertail cactus (Opuntia basilaris), and Agave ‘Blue Glow’.’

A portable cold frame like this on The Home Depot protects plants from the worst winter weather. On warmer days, remember to open the vents for essential air circulation.

Garden cloches (like these at Walmart) offer the same protection. Any leftover glass panes from renovations and plastic sheets over garden hoops make budget-friendly DIY cloche alternatives.

Alpines in Pots

Move potted alpines for winter to protect containers from frost and freezing rain. Plants are more susceptible to freezes in containers and should not be left outdoors, as they risk sitting waterlogged when temperatures plunge during winter.

An ideal place to overwinter alpine plants in pots is an unheated greenhouse, alpine house, cold frame, or porch. Keep plants somewhere warm and dry. On warm days, open the doors or lids of the greenhouse or cold frame so air circulates freely, rather than sitting damp and humid to risk fungal problems.

If you don’t have an indoor structure, you can move pots under the eaves. For extra drainage, Morgan Brooks, the Founder and Editor at Plant Style Home, advises: ‘I raise every pot on pot feet or bricks and tilt it slightly so rain runs off, and I plant in a gritty mix of compost, sharp sand and fine gravel.’

You can get a pack of pot feet at Walmart to raise containers over winter. To prevent waterlogging, check each pot’s drainage holes before winter to make sure they are not blocked and are allowing excess water to flow away.

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FAQs

Do You Need to Water Alpines Over Winter?

Watering is a very delicate balance when overwintering alpine plants. The general rule is that they require very little water over winter, as you don’t want them sitting in waterlogged soil. Check the moisture levels every few weeks to avoid the soil drying out, especially when plants are protected from the elements.

‘Water when the mix feels dry about an inch or two down,' advises Jessica Mercer from Plant Addicts. ‘Pots in a cold frame or greenhouse can heat up quickly in afternoon sun and may dry out more quickly as a result.’

You can check the soil beneath the surface with your fingers, or a soil moisture meter available on Amazon is an alternative option that gives instant results.

November is a prime month to look around the garden, think about which plants you need to protect from frost, and how best to do it. Useful kit like cold frames, frost cloth, and mulch helps protect plants in beds and borders.

Plants both large and small need some TLC ahead of winter. It may be that larger tender plants need wrapping in November, such as tree ferns, banana trees, or tropical hibiscus. For this, use frost cloth, burlap, or special winter plant covers.

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