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How to grow Adiantum
One of the most popular of all ferns, adiantum is grown for its finely textured, elegant foliage often held on glossy, black stems. Of the many hundreds of species, a large proportion are from tropical and subtropical climes and best grown as houseplants in the UK. Others come from cooler, temperate parts of the world (including Europe), and can be grown outdoors.
All species enjoy plenty of moisture and varying degrees of shade (see below). The genus can also be known by its common name of maidenhair fern.
Key Information
| Species | Hardiness | Notes | |
Houseplant | A. raddianum | H1C | 5°C to 10°C | Can be moved outside during summer. |
A. capillus-veneris | H3 | -5°C to 1°C | Can also be grown outside in mild, protected areas. | |
A. hispidulum | H4 | -10°C to -5°C | Can also be grown outside in mild, protected areas. | |
Outdoor plant | A. pedatum | H5 | -15° to -10°C | A tough, robust plant which can withstand some drought. |
A. aleuticum | H5 | -15° to -10°C | Fronds tinged pink when young. | |
A. venustum | H7 | -20°C and below | Extremely hardy. Mostly evergreen, although deciduous below -10°C. | |
Position
Soil Conditions
Hardiness
Where & when to plant Adiantum
For growing outdoors, best results come from planting in autumn or spring. An autumn planting can be done by those gardening in mild conditions (and broadly speaking, this is the southern half of the UK). For those liable to cold winters, it is best to wait until spring (generally the northern half of the UK). Planting can also be carried out in summer, though be prepared to water regularly.
Go for a shady, moist yet well-draining spot, such as a woodland garden, streambank, the base of an old stone wall, or any moist, partially shaded border. Adiantum also does well in a pot, as long as it is kept well-watered.
Indoors, the best time to pot up plants is spring.
Most houseplant species of adiantum originate from humid, warm environments, and so do best in steamy parts of the house such as the bathroom or kitchen. Choose a spot out of direct sunlight (so not on a sunny windowsill), though which receives indirect light (i.e., not deep, dark shade). The ideal is perhaps set back a couple of metres from a sunny window, or on a north-east or north-west facing windowsill.
How to plant Adiantum
- For planting in the garden, dig the soil area removing any large stones and weeds and breaking up any lumps. It can be a good idea to mix in some organic matter such as manure or garden compost at this stage, particularly if you have poor or heavy soil.
- Rake level and firm with your heels. Rake level again.
- Water plants well and allow to drain before planting.
- Dig a hole twice the size of the root-ball.
- Place the plant in the hole, ensuring the top of the root ball sits level with the surface of the soil. Too low and the plant may rot, too high and the roots can dry out.
- Backfill with soil and firm in gently with your foot.
- Soak well with water.
- Mulch around the base with well-rotted organic matter.
- For planting in containers, first choose an appropriately sized pot. The best practice is to start just a few centimetres larger than the rootball and increase in size every year or two. Always ensure there are plenty of drainage holes in the bottom.
- If you are using a large or heavy pot, it can be a good idea to fill and plant it in situ to save yourself the trouble of moving once full.
- Use a good quality potting compost with some horticultural grit mixed in and, if not already present (check the labelling on the bag) some slow-release fertiliser granules.
- Start by partially filling the pot with compost; enough so that when placed on it the upper surface of the root ball is about 3cm lower than the top of the pot.
- Fill around the plant with compost, firming down with your fingers then adding a little more so it is held tight.
- Pick up the container (if you can!) and lightly tap on the potting bench or ground a few times to help further settle the compost around the plant.
- Soak well with water.
- A mulch with horticultural grit will look attractive and help to prevent a ‘cap’ or crust forming on the top of the compost (something container plants can suffer due to the artificial nature of their watering).
What to plant with Adiantum
Outdoors, use hardy adiantum species alongside a variety of other moist shade lovers to create a lush foliage display. Try other ferns such as blechnum and dryopteris, along with hostas, asarum, rodgersia, and – one of our favourite secret-weapons for these conditions – luzula.
Inside, pair the more tender adiantum with other shade-tolerant foliage houseplants such as colocasia, solenostemon, and cyrtomium.
How to care for Adiantum
Pruning and Deadheading
Adiantum requires little attention. Many of the deciduous species will die back naturally without the need for pruning, and evergreen species need only the occasional removal of tatty, old fronds. Do this in spring before the new fronds unfurl, snipping off cleanly at the base.
Watering
Adiantum enjoys moist conditions and so, when grown outside, benefits from a good watering in on planting and then regular soakings until established. After this it should need watering only in hot, dry conditions. Allowing the top few centimetres to dry out between soakings is a good rule of thumb to avoid overwatering. To check this, wiggle your finger down into the soil until you hit a cool, damp bit.
Grown in a container indoors, adiantum needs watering frequently throughout the growing season (roughly March to September). Again, aim for consistently moist but not soggy compost using the ‘finger check’ technique above. Be aware that in hot weather, containers may need watering more often than you might think (particularly smaller containers which can dry out very quickly). As growth slows in autumn reduce watering to the bare minimum, i.e., just enough to prevent the compost drying out completely.
Feeding
On healthy, fertile soil, a mulch of well-rotted organic matter (i.e., a layer of leaf mould, manure, or garden compost applied to the soil around the plant) should provide enough nutrients for your adiantum. This has the added benefit of suppressing weeds and locking in moisture. Mulch when planting, and then again each spring.
If you garden on poor soil or your adiantum looks in need of a boost, applying a general-purpose granular feed to the surface of the soil and lightly working in can reap benefits. This is known as a top dress and should be done to coincide with mulching in spring – first apply the feed, then cover with the mulch.
Container-grown plants are different as they rely solely on the gardener for nutrition. Get off to a flying start by making sure you use a good quality compost with slow-release granules mixed in. These generally provide nutrients for around 6 to 8 weeks, after which you’ll need to apply a balanced liquid feed every 2-3 weeks until the end of the growing season (i.e., September-ish).
Remember to repot your adiantum every few years into a slightly larger pot using fresh compost. In the intervening years, it’s worth removing the top few centimetres of compost each spring and replacing with a fresh mix of compost and slow-release granules.
Cold Protection
Because there are so many different species of adiantum occurring in a range of climates, it is important to know the hardiness of your species and what this means for its ability to get through a UK winter.
Adiantum rated H1C needs to remain above 5°C all year. It’s best grown indoors, though can be moved outside during the warmer summer months. Here it will benefit from both increased airflow and the help of birds and insects to keep pests at bay.
H3 rated adiantum struggles any lower than -5°C. It can be grown outside in mild areas (e.g., around the coast, or in the microclimate of a walled garden), otherwise is best overwintered indoors.
H4-rated adiantum can cope with temperatures dipping to between -5°C and -10°C, so should be fine outside in an average UK winter. It may struggle in very harsh winters, particularly in gardens where drainage is poor, and the roots sit in permanently wet soil. As a container plant it is more vulnerable, and it can be worth wrapping the pot in bubble wrap, fleece, or hessian to protect the roots against frost.
Adiantum with a H5 rating can endure temperatures between -10°C and -15°C, so will cope with winter throughout most of the UK unless grown in a very cold or exposed location. Protect container-grown specimens as above.
Adiantum rated H7 is as hardy as it gets (to -20°C and beyond), so can be relied upon to get through a UK winter without concern.
Pests and Diseases
Outside, adiantum is considered trouble-free. Indoors, scale insects can be a problem. As always, we recommend the first line of defence to be taking the time to get the growing conditions right, as healthy, thriving plants are considerably less susceptible to pest infestations.
Scale insects flourish in dry conditions, so keeping your adiantum in a humid environment or regularly misted will help to ward these off.
How to propagate Adiantum
The recommended way to propagate adiantum is to divide the creeping rhizomes in autumn or early spring. These are the horizontal stems that sit on or just below the surface of the soil.
- Sever a rhizome from the parent plant.
- Cut into lengths 5-7.5cm long, ensuring each section has some roots attached and at least one growing point (i.e., a bud).
- Plant each section individually into a seed tray or 9cm pot filled with a well-draining mix. Make sure it is at roughly the same depth as it was previously – planting too deep can cause rotting.
- Water lightly and place in somewhere in light shade. For hardy species this can be outside or in a coldframe. For the more tender species, keep in a heated environment such as a propagation unit or on a sunny windowsill.
- Grow on until large enough to be planted or potted into an eventual location, always keeping the compost moist yet not soggy.
* Many plants carry Plant Breeders Rights and cannot be propagated for commercial purposes.
Common Adiantum questions
- Is adiantum dangerous for my pet cat?
This fern has no toxic effects reported and is on the Cats Protection list of safe houseplants. - Is there an adiantum species native to the UK?
There is, though ironically capillus-veneris is not hardy throughout the whole of the UK – only the mild, south-west where it can be found growing naturally.