How to grow Ilex
Also known as holly, ilex is best known as a prickly-leaved evergreen with festive berries, however there is much more to this large, varied genus. Did you know, for example, that some hollies are not evergreen at all, but deciduous? There are also many species with smooth, non-prickly leaves (perfect for where children and pets roam), and berries in shades not just of red, but orange, yellow, and black too. Some grow very large and make imposing specimen trees, while others remain small and are suitable for containers or clipping.
While some forms of holly are self-fertile and able to produce berries in isolation, most are either male or female, with only the females capable of fruiting. A quick warning – don’t be misled on this matter by cultivar names. For reasons unknown, ‘Golden Queen’ is the name for a male form, while ‘Golden King’ is female.
Holly is a slow growing plant which, while probably ruling it out for urgent screening purposes, has many benefits – namely ease of maintenance.
It is worth noting at this point that the berries can be toxic to humans and pets if ingested.
Zantedeschia is a genus of flowering plants from the family Araceae and is native to southern Africa. With a rich history dating back to the Ancient Romans, these deciduous or semi-evergreen perennials have been used as a symbol of celebration. Zantedeschia was Named after Professor Giovanni Zantedeschia, an Italian botanist.
There are two main forms of Zantedeschia: hardy and tender. Hardy forms of the plant can be grown outdoors, enjoy moist soil and full sun or partially shaded conditions - these are known as Arum lilies. Tender forms of Zantedeschia prefer being grown in containers or pots and should be brought inside over the winter - these are known as Calla lilies.
With tuberous flora in all colours from whites, yellows and oranges to deep reds and purples, Zantedeschias are not to be overlooked in any garden, as long as they have sufficient sunlight to grow in.
Ready to learn more about growing Zantedeschia? Read on for all there is to know...
Key Information
Soil pH
Position
Hardiness
Species at a glance
Most widely grown Ilex aquifolium (our UK native holly), now with hundreds of cultivated forms available.
Self-fertile I. aquifolium ‘JC Van Tol’ and I. aquifolium ‘Pyramidalis’ will produce plenty of berries without the need for different male and female plants.
Smooth leaved I. x altaclerensis and its cultivars tend to be the least prickly, with large, handsome leaves. This hybrid dates back to a few hundred years ago and is a cross between UK native I. aquifolium and a species from the Canary Islands called I. perado.
Best alternative to box I. crenata is widely grown as a substitute for the beleaguered Buxus sempervirens. It has small, rounded leaves and takes well to clipping and topiary.
‘Blue’ leaved I. x meserveae is also known as ‘blue holly’, its leaves so dark they appear almost blue in winter.
Chestnut leaved I. x koehneana ‘Chestnut Leaf’ is a popular hybrid with unusual, distinctly chestnut-like leaves. Faster growing than most.
Deciduous American species I. verticillata and I. decidua both lose their leaves over winter. Neither are widely grown in the UK, though they offer good garden value. Ones to watch..?
Unusual berry colour I. aquifolium ‘Bacciflava’ is probably the best yellow-fruited holly, while I. aquifolium ‘Amber’ is a popular orange form.
Where & when to plant Ilex
Position - Happy in full sun or partial shade. Variegated forms develop the best colour in full sun. Can cope with wind exposure, including coastal winds.
Soil - Will succeed in most soils, apart from very wet or very dry.
Flowering Period - Spring to early summer
Hardiness - The majority of species are very hardy, rated H6 or above. H6 means capable of minimum temperatures between -15 and -20°C.
Having said this, there are a handful of less hardy species, so it’s always worth doing a bit of research on your chosen variety.
Holly is best planted in late winter or early spring. Planting can be carried out at other times of year, though be prepared to water frequently – especially for a summer planting.
Use holly in a woodland garden or as a specimen tree, perhaps in a lawn. Larger forms can be clipped into an impenetrable hedge or windbreak screen, and smaller forms into ‘lollipop’ standards, topiary shapes, or whatever takes your fancy. These more compact types will also grow happily in a container.
How to plant Ilex
- For planting into the ground, start by watering the roots well and allowing them to drain before planting.
- Dig the soil area over, removing any large stones and weeds and breaking up any lumps. Mix in a generous amount of organic matter such as manure or garden compost.
- Rake level and firm with your heels. Rake level again.
- Now dig the planting hole, aiming for twice the width of the rootball.
- Place the plant in the hole, ensuring the top of the rootball sits level with the surface of the soil. Too low and the stem can 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 such as manure or garden compost.
- For planting in containers (remember, smaller forms are best, and those without prickly leaves are easier to repot), first choose an appropriately sized pot. The best practice is to start just a few centimetres larger than the root ball and go up in size gradually every few years. Always ensure there are plenty of drainage holes in the bottom.
- Again, water the roots thoroughly and allow to drain before potting.
- It can be a good idea to fill and plant your pot in situ to save yourself the trouble of moving it once full.
- Use a good quality, loam-based compost with some horticultural grit mixed in, and, if not already present in the compost (check the description on the bag) some slow-release fertiliser granules.
- Start by partially filling the pot with compost; enough so that when placed on it the top of the roots sits about 3cm lower than the top of the pot.
- Infill all the space surrounding the roots with compost, firming down with your fingers then adding a little more so the plant is held tight.
- Pick up the pot (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 Ilex
Grow holly in a mixed, native hedge with companions such as hazel (Corylus), beech (Fagus), and dogwood (Cornus).
Alternatively grow alongside other plants with colourful berries, creating for a feast for the eyes and the birds. Think skimmia, aronia, leycesteria, and callicarpa.
How to care for Ilex
Pruning and Deadheading
The pruning of holly varies according to how it is grown:
Free-standing specimens benefit from a little light shaping in their early years (in late winter to early spring), then are best left to their own devices apart from the occasional removal of dead, diseased, damaged, or badly placed growth.
Holly grown as a hedge can be trimmed once a year. Some advice advocates doing this in early spring, but we prefer an early autumn timing to avoid harming nesting birds.
Holly grown as a formal shape can be clipped in summer.
Overgrown holly can be given a hard prune (i.e., cut down to just about ground level) in late winter or early spring. It will respond to this by sending up new growth, often bearing extra prickly leaves.
Variegated forms can be prone to reversion, where pure green leaves are produced rather than the desired bicolour. These shoots tend to be extra vigorous and should be pruned out as soon as you spot them.
Watering
Like all woody plants, holly should be regularly watered during its first couple of growing seasons in the ground while its roots become established. After this it is known to be drought tolerant and should require watering only in prolonged periods of hot, dry weather. An annual mulch is also useful for locking in moisture – more on this in our ‘Feeding’ section below.
Container-grown holly has less access to moisture so will need to be regularly watered throughout every growing season. Allowing the top couple of centimetres of compost to dry out between watering is a useful rule of thumb to help avoid overwatering (holly hates to sit in soggy compost), though be aware that during the height of summer this can happen in as little as 24 hours. Wiggle your finger into the compost to check. From mid-autumn, the British climate tends to take over watering needs, though do remember to step in in the event of an unseasonably dry spell.
Feeding
To give it the best possible start, feed holly for its first couple of years in the ground with a general-purpose granular feed applied to the surface of the soil and lightly worked in (known as a ‘top dress’). This is best done in late winter, along with a mulch of well-rotted organic matter. By this we mean a layer of manure or garden compost applied to the soil around the plant), which, as well as improving the soil structure and nutrient content, also suppresses weeds and locks in moisture.
Once your holly is well established an annual mulch should provide sufficient nutrients, however, apply a top dress as above if ever you feel an extra boost is needed.
Container-grown plants rely more 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, then throughout the growing season (March to September) apply a monthly liquid feed. An annual top dress is also advisable: each spring, scrape off the top 5cm of compost and replace with fresh.
Cold Protection
Most popular holly species are hardy enough to withstand even a very cold UK winter without the need for additional protection.
Of those most widely grown, the least hardy is the chestnut-leaved holly with a rating of H5 (-10 to -15°C). This should still be fine in most UK situations, though if grown in a container it may be worth insulating the roots if you’re in a very cold, exposed spot. Hessian, horticultural fleece, or bubble wrap all work well, and this offers the added benefit of protecting the pot from frost damage.
Pests and Diseases
Though a tough, robust plant, holly does host a few pests. Its young shoots can be susceptible to aphids, and you may notice the presence of scale insects and leaf miners on evergreen species.
Small populations of these are unlikely to do harm and should be tolerated. As always, we recommend the best line of defence to be creating a healthy, balanced garden ecosystem by encouraging as many species of insects and mammals into the garden as possible. Natural predators of these pests include ladybirds, wasps, and birds, so try to boost their numbers by growing a wide range of pollinator-friendly plants, not using chemicals, and providing suitable habitats.
How to propagate Ilex
Holly is best propagated by semi-ripe cuttings in late summer to early autumn, using growth that is becoming firm and woody at the base but is still flexible at the tip.
- Snip cuttings off the plant, if possible taking a longer piece than the ideal eventual length of around 10cm (to allow for trimming).
- Put them in a plastic bag straight away to prevent drying out.
- Fill several pots with a well-draining compost mix.
- Trim the end of the cutting to just below a node (point at which leaves grow).
- Remove all but the top 2-4 leaves.
- If the remaining leaves are large, cut them in half with a sharp knife (to reduce water lost through transpiration).
- Insert the cuttings into the compost and water lightly. Several cuttings can be put in the same container if there is enough space to do this without them touching.
- Place in a greenhouse or propagating unit if you have one or covered with a plastic bag on a windowsill if not (out of direct sunlight).
- Keep the cuttings misted and occasionally watered until they root. You will know this has happened when roots emerge out of the bottom of the container – expect this to happen the following spring.
- Gently remove rooted cuttings and pot them into individual pots. Grow on in a cool yet frost-free environment such as an unheated conservatory, greenhouse, or cold frame, until they are large enough to be planted out.
* Many plants carry Plant Breeders Rights and cannot be propagated for commercial purposes.
Common Ilex questions
How fast does ilex grow?
Holly is a relatively slow-growing plant, with an annual average growth rate of 10-20cm.
Does ilex need full sun?
No, it is equally happy in partial shade – however, the leaf colour of variegated forms is more vivid and intense in full sun.
Deep shade is best avoided.
Is ilex an evergreen?
While the majority of the 400 or so species are evergreen, there are a handful of deciduous forms.
Do birds eat holly berries?
Yes! While they are toxic to humans and pets, birds can digest a few holly berries at a time without issue. Red are the favourite (usually all gone by December), while the evidently less appealing orange and yellow type often remain untouched until the new year.
Can a holly be transplanted?
Yes, this is best done in late winter or early spring. Dig up as much of the rootball as you can, leaving plenty of soil attached to aid a quick and successful establishment in its new location.
Where can I learn more about ilex?
RHS Rosemoor in Devon holds the national ilex collection. Here you may see examples of many different species and cultivars, including the more unusual deciduous forms.
My holly tree has differently shaped leaves at the top. Is this normal?
Hollies often have smoother, less spiny leaves towards the top of the tree. If you’re after a prickly, intruder proof barrier it can be best to grow holly as a hedge – the regular trimming will generate spiny foliage and extra dense growth.
