Here are some examples of easy to grow plants which will flower easily in the UK even when quite young. Most of the photographs are of plants in 3" pots. Most of them will grow well in a well drained compost such as an equal mixture of soil based compost and sharp 2mm grit sand. They do not like wet feet, but in summer when growing actively need almost as much water as normal house plants. Reasonable advice is to water once or twice a week if the compost has dried out. It is far easier to kill a plant by overwatering than by underwatering. In winter dormant plants do not need any water at all provided they are kept fairly cool in the range 5-10C. When grown as house plants in a centrally heated home they may need some water to avoid excessive shrinkage.
I quite like the group Notocactus, which includes many easy to grow and free flowering species. They are globular or short columnar plants from South America now lumped with Parodia. Most have large yellow flowers and grow easily. A few are a bit more tricky. Some of the nicest plants have unusual blue grey bloom or purple magenta flowers. The magenta colour is particularly hard for colour films to render accurately. Some Notocacti clump up to form an impressive group when they get older, and others have the irritating habit of becoming corky from the base. They do give excellent displays of flowers from relatively small plants.
Some of my plants in flower
Notocactus species showing a typical golden yellow flower with bright red stigma lobes.
Notocactus mammulosus showing a bright lemon yellow flower wide open in the sunshine.
Notocactus roseoluteus - a very pretty plant with bicoloured pale pink silky petals with a yellow centre.
Notocactus sp. HU238 another strong yellow flower contrasts with a glossy green body.
A tray full of four year old Notocactus tabularis seedlings all in flower together. I have experimented with planting them outside in a well drained sheltered border against the south wall of my house. They grow much more slowly and flower later but can survive all but the very worst of British winters. They set seed easily and profusely and grow well from seed reaching flowering size in about 4 years.
Notocactus ubelmannianus has a splendid glossy mid green body bears a ring of the most amazing magenta to royal purple flowers every spring. There is also a pale yellow flowered form and I would like to acquire a one sometime. All the seedlings I have ever had were this splendid colour. The true colour is somewhat different to the picture as none of the colour films I have tried can accurately capture this wonderful deep colour. It looks surreal!
There are some more pretty cacti and succulents in flower on the next page
You should also visit Tony Mace's fantastic Cactus Mall which is the most comprehensive and informative site for the hobby with links to virtually everything on the net relating to cacti and succulents.