Almost all the ageratum sold is the squat dwarf bedding sort, useful in a window box and no use at all for cutting. 'Timeless Mix' is the florist's form, with straight stems at 60 to 70cm that are long enough to harvest, carrying the same soft fluffy buttons from June through to October.The flowers are why it earns its bed. They hold their shape in water and do not shatter, which is rare in anything this fluffy, and the powder blue is a genuinely difficult colour to find in a cut flower. The mix also gives pink, violet and white. If it is only the blue you are after, be aware you will be growing a fair few of the others alongside it.It is half-hardy, so it needs a frost-free start and cannot go out until the risk has passed. Left alone a plant makes one central stem and stops. Pinch the tip out while it is young and you get the branching that turns it into a cutting crop. Keep cutting and it will run right into the autumn.
