Summertime BLUES ? I love them!
Treat them right, and agapanthus will give you starry bursts of beautiful blue flowers on 4ft stems all summer, says Monty Don
MY AGAPANTHUS have flowered this summer like intense star bursts, mostly blue with a few pure white varieties for good measure. I could not have asked more of them. This success is down to the right blend of neglect and nurture, and once you have that combination in its right balance, gorgeous agapanthus are almost guaranteed year after year.
For a start I always grow them in pots. My rich Herefordshire loam is far too good for the likes of them and would only result in a mass of foliage and a complete absence of flowers. Agapanthus will only flower well when their roots are stressed either by low fertility or lack of space.
I pot them into a very welldrained compost mix (which means adding as much grit by volume as peat-free compost), with no more than an inch or so between the roots and the walls of the pot. Do not repot them again until there is literally no room for any compost in the pot. They will flower at their best when the roots have grown to form a solid mass pressing hard against the pot sides. Indeed, it always used to be said that the time to repot an agapanthus was when the pressure of the roots cracked the pot apart.
But they do need watering weekly, and I also give them a seaweed feed – which is high in potash but low in nitrogen – once a fortnight. This will encourage extra flowers to form without promoting too much extra foliage. If you cannot get hold of liquid seaweed then a tomato feed will do the job as well.
Of course, in a climate such as that of their native South Africa, Spain or Portugal you often see them flowering profusely on roadsides. But they are not hardy and I always bring my pots in when the first frosts are imminent, and do not put them out again until mid-May.
However, deciduous agapanthus, which die right back each winter, will withstand frost down to about -10°C, especially if mulched with a protective layer. Even if the roots become frozen, they should survive as long as they thaw gradually.
We grow the deciduous Agapanthus campanulatus, which has small flowers of a particularly intense shade of blue growing on 4ft-high stems, and slightly glaucous leaves.
Evergreen agapanthus such as A. praecox and A. africanus are less hardy and, as they need protection from all but the lightest frost, are best grown in a container. If you have space, putting your pot in a cold frame or greenhouse is ideal, but horticultural fleece will do in milder areas.
‘Headbourne hybrids’ are a cross between deciduous A. campanulatus and evergreen A. praecox. They’re hardier than the evergreen species but have more flowers than A. campanulatus with a greater vibrancy of colour than most deciduous types. I grow ‘Loch Hope’, which has narrow leaves and plenty of dark blue flowers on a 45ft stem, and ‘Polar Ice’, which has pure white flowers that seem to last for ages – certainly from July through to mid-September.
Agapanthus hybrids form the new buds for next year’s display shortly after the existing flowers set seed, so new plants should be kept watered and fed until autumn to keep them strong. You can collect and sow the seed but they may give you a mass of somewhat muddy colour, effectively combining the worst of the parents rather than the best. For most of us it’s much more effective to propagate by division in spring and accept a flowering delay until the following summer while the new plants get established and start to feel happily constrained in their new pot.