I write about these bulbs almost every summer because they are so easy to grow and are so important for fall colour and because August is the only time of year to plant these giant crocus that bloom in September. Fall blooming colchicums go by the name of 'Autumn Crocus', although they are not really a crocus at all. In fact, they belong to the lily family and are native to the Mediterranean region.
Colchicum bulbs become huge and can, over time, produce 19 to 25 flowers, one right after the other, until they all open in a profusion of colour. A lady, who used to grow thousands in her backyard in Vancouver, told me it takes about two years for a small bulb to grow into a huge specimen, at which point it splits into four smaller ones. Small bulbs will produce five to seven flowers; mid-sized bulbs will have about a dozen blooms.
I have learned the hard way that these bulbs love a sunny, well-drained, yet moist location, with average soil. One year we planted them in several shady spots, only to have them gradually deteriorate to the point of no return. You can leave them in the ground to naturalize, if that is the effect you wish to have. A single corm of a large colchicum hybrid can easily multiply to cover nearly 900 square centimetres of garden. Just imagine what a few well-placed groupings throughout your garden can do. It is best to plant them about 10 cm deep and about 15 to 20 cm apart. They need some room, not only to multiply, but also for the huge foliage which will develop the following spring.
These fascinating bulbs can actually bloom indoors simply by leaving them sitting on a windowsill. It's best to put them in a saucer on about two inches of gravel. The flowers won't last quite as long, nor will they have the same intense colour, but they will bloom and can still be planted outside to grow on for next year. Each year in late April, just as the tulips are nicely in flower, huge masses of strap-like leaves appear and grow to about one foot in height. After two to three weeks, they disappear as suddenly as they arrived, having provided all the food the bulb needs.
Colchicums are quite hardy and do well from zones one through nine. 'Colchicum speciosus', which blooms in September and October, is most often a bright violet-pink, while 'Colchicum album' is the seldom seen beautiful white variety. Among the hybrids, 'Lilac Wonder' is the most popular with its attractive lilac-pink flowers. The double purple blooms of 'Waterlily' are unusual and quite beautiful, but its heavy blossoms are often knocked down and spoiled by autumn rains.
Colchicums should be planted in areas where they can be naturalized without interfering with other plants. Underplantings around flowering shrubs, like white altheas or P.G. hydrangeas, make a lovely contrast when the bulbs bloom each fall.
I know there are many gardens out there that really need a lift in September and these precious fall crocuses can add that little spark of colour.
