In this article, we will be discovering how to grow Helianthemums (Rock Rose) in containers. The plants of this genus are either half-hardy perennials or hardy shrub-like perennials. There is a gap in summer displays in containers, where small shrubs that flower in summer are far between. The rock rose thankfully fills this gap, where they grow up to 30cm in height. They are Mediterranean alpines where from late spring to late summer, the plant is covered in white, yellow, or orange disk-like blooms. The flowers can also be scarlet or even bronze.
The flowers are spectacular but the leaves of elongated oval complete the plant. The leaves can be either green or silver-like and they are evergreen also. There are many species to grow either from seed or from shop-bought garden-ready plants. They are fast-growing plants and are ideal for containers in a sunny location. It may be known as Rock Rose such as Sun Rose or Frostweed.
GROWING HELIANTHEMUMS IN CONTAINERS
As with a lot of plants, you have a choice as they can be either grown from seeds or you can buy shop-bought plants. Seeds of hardy perennials can be grown directly outdoors in autumn or they can be sown indoors before first frosts for the half-hardy perennials for planting outdoors after the final frosts of spring have passed.
GROWING FROM SEEDS
Eight weeks before the final frost date of spring, you can sow Helianthemum seeds indoors. To do this, fill a seed tray with a good quality seed sowing compost. And water it in. You can then sprinkle the seeds on top of the compost, thinly. Cover lightly with more sieved compost and then place a propagator lid on top. Place the seed tray on a windowsill and within 3 weeks the seeds should germinate.
When they are large enough to handle, you can prick them out and transplant them individually into 7.5cm pots full of multipurpose compost. After 8 weeks they should be large enough to be hardened off and then they can be planted outside.
PLANTING IN CONTAINERS
At this stage, you can plant tour home-reared seedlings and shop-bought plants in exactly the same way. Buy a suitable container that will suit the plant in question, but make sure it is full of drainage holes. Fill it with a 1cm layer of gravel to help drainage and then fill the rest with any multipurpose compost. They will grow in poor soil but will not do well if it is too wet.
Dig a hole that is slightly larger than the root ball it came in the original housing. Place a plant so that the top of the root ball is at the same level as the top of the surface of the compost.
Backfill with the growing media, ensuring that any gaps that remain are filled with more compost. Firm it in and water well.
They can tolerate drought when well established but otherwise when 5cm below the top surface of the compost feels dry, then it is time to water. As they prefer poor soil, do not fertilize unless the plant is showing obvious signs of a deficiency of nutrients (see my article on the signs for this)
The plant tends to look shabby once flowering has finished. In this case, it is advised to cut back to one-third of the original height, once the first round of blooming has finished. If this is done on time, you may be lucky and get a second flush of blooms later in the growing season. The flowers may only last a day but many more will be produced, especially so if you deadhead frequently.
The container must be placed where it sees the most sunlight, at least 6 to 8 hours.
PESTS AND DISEASES
These plants are not readily attacked by pests or pathogens, but in hot summer powdery mildew can be a problem. If you ensure that air can circulate around the plant and you prune after flowering, then this problem should be minimised.
VARIETIES TO GROW
There are several varieties to grow and most are based on Helianthemum nummularium:
‘ Ben Afflick’ provides orange-yellow flowers, whilst ‘Ben Fhada’ has silvery-green leaves and primrose-yellow flowers.
‘Firedragon’ has flame-coloured flowers, whilst ‘Georgeham’ has pink flowers with yellow- centres.
‘Peachy Keen’ produces double-flowered, peach coloured flowers, whilst ‘Wisely Pink’ has pink flowers. ‘Wisely Primroses’ is a variety with grey-green leaves and primrose-like yellow flowers.
In this article, we have discussed how to grow Helianthemums in containers. This is a useful plant to have as a summer container display, where many colours can be brought in a compact form. It is easy to grow from seed or shop-bought plants where many varieties are possible,
If you have any questions or comments that you wish to make on growing Helianthemums in containers, please do so in the comment box below.
Happy Helianthemum growing.