We talk here of only one group of Ranunculus - a huge family - and that is the group known as Ranunculus asiaticus. This group of Ranunculus grow from tubers - though they are often referred to as Ranunculus Bulbs - flower in spring and die down for the summer months.
These Ranunculus offer a welcome splash of many colours from March until April. They are easy to grow, but so many gardeners fail with them. They are generally to be found as potted flowering plants in garden centres during the late winter or early spring.
These turban-flowered or Peony-flowered Ranunculus are especially suited to growing in containers - from flowering plants bought at the garden centres, and such is their normally low price, that you will have to consider if it is worth the bother trying to store the Ranunculus bulbs them for late summer and early Autumn!
As can be seen from the Ranunculus images above, the colour range is fantastic, and of course, they are a photographer's dream flower. There are many other flower colour variations, and the great thing about buying them as flowering plants, is the fact that you can rummage around the display and choose those that suit or appeal.
These Ranunculus can be bought as tubers in the Autumn and grown in individual pots by planting and over-wintering in a cold green house. Best to soak the claw-like tubers or bulbs for 24 hours before planting. The plants will show signs of growth quite soon, and should be kept under protection for the worst of the winter. They can then be planted out into the garden during late February or March, when the flower buds will probably be showing through.
Ranunculus asiaticus prefer a position of full sun, though if simply grown as a one-year plant, can be planted almost anywhere. If long term growth is the aim, then remove the old faded flower right after demise, and keep the plant watered throughout the early summer - until it dies down. The glaucus finely cut leaves will start to appear again in the late Autumn and will remain throughout the winter.
Ranunculus bulbs are ideal as 'fillers' for the patio containers, where they will mingle well with early flowering tulips or plants such as Myosotis. If grown in containers, then best regarded as a one-off job - to be replaced the following Autumn or Spring.
The height of these Ranunculus is around 6 8 inches - 15 20cms - though can get to a gangly 10in - or even a 12in plant if previously forced or grown too close together.
Ranunculus can be bought as seed, and should be sown in gently heat during September-October. Pot into single pots - three and half inch as soon as seedlings are large enough. The earlier sowing will produce better plants for the flowering season in the following spring. Sow and grow under glass for the whole of the winter season - growing cold without heat - though frost-free for the winter months. They will be flowering size in the Spring following.
If bought as tubers, then treat as mentioned above.
Division of Tubers. Once the Ranunculus have formed clumps - after two - three years, the tubers can be divided just after the foliage dies down in late spring.
If grown under glass, then powdery mildew can be a problem. Keep air vents open on milder days and encourage good ventilation. Use a general fungicide as a preventative measure from potting time onwards.
They make a seemingly tasty meal for slugs and snails which are generally short of tit-bits in the late winter early spring.
Over-watering during the winter months will materialise in yellowing of the foliage. Needless to say, if this occurs, then cut back on the winter watering - which should be at a minimum in any case.
Container grown plants may suffer from an attack of the Vine Weevil Beetle Larvae. The first sign being the sudden wilting of the plant.