Hellebores enjoy well-drained, moisture-retentive soil, rich in organic matter under deciduous plants that will protect them from the full sun in summer. They prefer neutral to alkaline soil but will do OK in slightly acidic too. Any other details will depend on the cultivar of hellebore, for example, the newer hybrids with marbled leaves will be happier with more sun than traditional (orientalis-type) hybrids. Each species will also have their own preferences (e.g. H. lividus likes more sun, H. niger prefers less but both prefer less water than others). See Dispelling myths and assumptions for more information on where hellebores come from.
In pots, use compost that mimics these conditions. Use a really good quality peat-free compost as a basis. You can add soil, leaf mould, composted bark, garden compost etc. but make sure it is also free draining. I use potting bark for this. If potting H. lividus or H. x sternii that like really free draining soil, add horticultural grit. Feed regularly in spring and autumn. In the summer, move them to somewhere more shady.
Hellebores have a massive amount of thick roots, so if you intend to keep a garden hybrid in a pot, be prepared to work your way up to a 10 litre pot in 5 years or so. Some cultivars are smaller and more suited to pots. Repot each year as the roots fill the pot it is in.
This image shows a seedling that is less than one year old, next to a normal 9cm pot. If it can grow roots like that in less than 12 months, imagine what they look like when mature!
Don’t plant hellebores too deep or they won’t flower. The knobbly top of the root growth, where the growing points are, should be below the surface, just covered. Nor should they be planted too shallow, the crown does need to be covered so it does not dry out.
Cut the leaves away of flowering-age garden hybrids before Christmas. This is so you can see the flowers clearly but also to remove any traces of black spot, which can infect flowers and stems especially in a wet winter. Some species, such as H. niger, will just need a tidy up. Species that have flowers and leaves on taller stems (i.e. H. argutifolius and H. lividus plus H. x sternii) can have the flowering stalks cut back when the flowers start looking scruffy later on in the year.
Keep an eye open for the hellebore aphid, often found on the aging flowers. They are rather large, usually green aphids at least 3mm long. They can transmit viruses, including hellebore Black Death. I squish them when I find them, they can increase quickly but possibly not as fast as the ones you see on roses or veg.
And if you don’t want one hundred seedlings to swamp your original plant, remove flower heads before the seeds ripen! Unless of course you’ve got an infertile interspecies hybrid, which so many of the new cultivars are.
Seedlings swamping parent plants are the most common cause of the question “Why has my hellebore changed colour?”
Why hasn’t my hellebore flowered this year?
Yes, sometimes they don’t. Perhaps conditions were not ideal while the flower buds should have been forming. Possibly too dry, or too shady, or not enough food if it’s in a pot (they are hungry plants). Mice and voles could also be a problem.
When divided or transplanted they might also take a break for a year, especially if that has happened later than mid spring.
Flower buds start to form over the autumn, when in their native environment they would have had the rains after the dry summer. So if you divide a plant in the summer, it may be trying to grow new roots and settle back in rather than trying to produce flower buds that year. The best time to divide is in early spring so the roots can grow before the quiet summer period. In the UK as we get a lot of rain, they may continue growing through the summer.
The same goes for transplanting them with a lot of root disturbance i.e. digging them up in the garden and moving them elsewhere. Do this in early spring and then you may get flowers the following year.
Occasionally you may get a proliferation of small leaves on a mature hellebore crown. This usually means it’s been through a tough time, often this happens in a pot and means the crown has got too dry. Or even too wet. The only way of ‘curing’ this I have found is to divide the crown and shock it back in to growing normally. I haven’t seen anyone mention another way to fix this.