How to grow gunnera
Grown for its spectacular, large architectural leaves, gunneras can make an excellent focal point along the margin of a large pond or add tropical-looking foliage to any garden. It is fairly easy to grow as long as the soil doesn't dry out in summer and the plants are given winter protection in-situ.
- Largest gunneras have foliage up to 2m (6⅔ft) across and 2.4m (8ft) tall
- Thrives in wet or permanently damp soil
- Likes a sunny, sheltered position
- Deciduous perennial, dying back to the ground in winter
- Crowns need protecting from frost overwinter
- New plants bought or obtained by division and seed
All you need to know
What is Gunnera?
Gunnera are hardy or frost tender
Perennials are any plant living for at least three years. The term is also commonly used for herbaceous perennials which grow for many years (To compare: annual = one year, biennial = two years).
Gunnera manicata is the most well-known species. It is one of the largest herbaceous plants grown in UK gardens. In some areas of the country, especially in the south west of the UK, this and its close relation Gunnera tinctoria have become somewhat invasive.
Gunnera manicata can be invasive when, particularly went planted along a water course. As a result it is listed on Schedule 3 of the EU (Birds and Natural Habitats) Regulations 2011 in the Republic of Ireland as an invasive non-native species. While this does not prevent it from being sold or from being grown in gardens in the Republic of Ireland, the RHS encourages those that do grow it to take great care with managing it and with disposing of unwanted material.
Stricter rules apply in the whole of Europe and UK for Gunnera tinctoria. It is an offence to plant or cause these to grow in the wild. It is banned from sale and gardeners growing this plant should undertake measures to control its spread beyond their garden, but you don't have to remove it if you have it; just control it.
The bold foliage effect created by the leaves are the most appealing aspect of gunnera, but the amount of space needed to grow certain species will determine which you plant in your garden.
- Gunnera manicata is perfect in large spaces where you want to create a jungle feel along with other dramatic foliage such as Darmera, Rheum and Ligularia. Plants typically reach 2.4m (8ft) tall and more than a 3m (10ft) spread
- There are smaller varieties. Gunnera magellanica is just 15cm (6in) tall and 30cm (1ft) wide). Gunnera hamiltonii is ideal for growing in containers or in open ground at 1.5m (5ft tall and a 2m (6⅔ft) spread.
- Bear in mind that if the temperature drops below -10°C (14°F), you will need to protect the crowns of Gunnera manicata (see Ongoing Care below)
You can also see many gunnera in all the RHS Gardens, with Gunnera manicata located near water features.
How to buy gunnerasGunneras are sometimes available in garden centres and nurseries, and from online suppliers, with a larger choice available by mail order.
You will find gunneras for usually sold as potted plants in spring, just as they begin to shoot from their knobbly crowns. Look for vigorous new shoots and healthy, green leaves without any brown tips. Smaller plants will take two or three years to establish and begin to produce bigger leaves. Sometimes larger plants are available at an accordingly larger price.
When to plant gunnerasPlant gunnera in spring, so that they have a full growing season to establish. However, they can be planted from spring until autumn as long as you water well in dry spells.
Where to plant gunneras
- As long as there is plenty of water at their roots in summer, a sunny or part shady position in thr ground will be suitable. In shade, the foliage will head for the light and tend to grow taller than it would in sun, helped by less moisture being lost from the foliage by the shade
- The larger gunneras quickly get too large to be confined to a container, but you can grow the smaller gunneras successfully in pots
- Plant in a site sheltered from wind and avoid cold areas (such as frost pockets) in a north facing corner of the garden
- The site needs to be constantly moist in summer, but this can be achieved by watering in summer if it gets dry. However, avoid places that get waterlogged in winter as the crown of the plant can rot
- Gunnera magellanica, once established, can tolerate drier conditions than the larger species
How to plant gunnerasIn the ground
To plant gunneras, use our guide to planting perennial plants.
After planting, mulch with well-rotted manure or garden compost annually and, in the second, spring feed larger species with general purpose fertiliser such as Growmore or poultry manure pellets for more vigorous growth.
Smaller gunnera grow well in containers and are easy to plant – see our planting guide below.
With gunneras in particular:
- Choose a container that is at least 20–23cm (8–9in) in diameter - eventually they will need at least a half-barrel sized pot
- Use peat-free multipurpose compost with added loam, or a loam-based compost. Mix in 30% extra horticultural grit or fine gravel to improve drainage
- Position in a spot sheltered from winds and keep well watered
Mature plants can withstand temperatures down to -10°C (14°F). In most UK town and cities gardens, these temperatures are rarely reached so the plants can survive unprotected. However in rural and northern parts of the UK, it is typical for the temperature to reach this cold temperature at least every few winters.
Newly established plants, in particular, will need protection from freezing conditions. The simplest method is to cut the leaves of the plant in autumn, remove their leaf stalks, and place them upside down over the crowns. Alternatively, cover the crowns with at least a 15cm (6in) layer of straw or bracken and hold in place with chicken wire or netting that's pegged down with with pieces of wire bent into U-shapes.
For large gunneras, look for section of the plant where there is an obvious rhizome (crown) with a shoot, growing away from the main part of the plant. This can be severed from the main plant. With larger gunner, this can first involve cutting through the fleshy rhizome, ensuring there is at least one shoot on the new section. You can then use a spade to dig up this new section with as many roots as you can manage - replant this into new ground, improved with organic matter such as garden compost or well rotted manure.
For smaller gunneras, it is often possible to dig up a section with numerous shoots/growing points, and just replant it in improved soil (i.e. you don't usually need the extra step of cutting through the rhizome as they are small enough for the spade to go through).
Slugs and snails may attack young growth.
If you’re a member of the RHS, you can use our online Gardening Advice service, via MyRHS.
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