33: Spring 2014

Author: Gary Dunlop

The Cultivation of Agapanthus

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The Cultivation of Agapanthus
Gary Dunlop

Only three species of agapanthus are commonly available, A. campanulatus, A. inapertus and A. praecox, which is often wrongly sold as A. africanus. All can be readily grown/cultivated in the open ground in the British Isles, despite some like A. praecox being from summer dry areas and others from summer wet areas. Most forms of these species should be reasonably hardy except in the coldest winters, which recent experience demonstrates can still occur.

The thick fleshy rhizomes and roots are essentially water storage vessels, which enable the plants to survive periods of drought even in seasons where they normally receive moisture. Thus they are particularly suitable for growing in areas with long dry summers. However, the rhizome and roots being a drought survival mechanism, also means that this can be compromised when agapanthus are lifted and divided, particularly with the larger species and forms, as they usually loose a significant proportion of the roots. The plants compensate by initially concentrating on making new roots. To facilitate this, agapanthus are best lifted and divided when in active growth, preferably early in the growing season or not later than at least a month before they are likely to go dormant. Division even when in full flower can be achieved without negative effect. Division when dormant can often result in the remaining roots and rhizomes rotting away if planted in cold wet soil, though it can be successful if the divisions are kept relatively dry and in frost free conditions.

Division of agapanthus rootstock is not for the faint hearted. The smaller forms of A. campanulatus can be dug up fairly easily or if the clump is large, simply part of the clump prized off and then prized apart using two forks. The smaller divisions can usually be broken apart further by hand. The larger species and forms are usually best sliced into with a spade and then prize the separated part of the clump out of the ground. Further division is then best done with cutting through the rhizome with a sturdy knife or the blade of secateurs. Division is more easily done before the leaves are fully developed. Some growth points are inevitably broken off in the process if done robustly, though the growth points of A. inapertus are more brittle than other species so they should only be divided just as the leaves are starting into growth.

There is much ill-informed advice given by so-called gardening experts about the cultivation of agapanthus. A hangover from Tudor times when A. africanus was first cultivated, and not hardy outside and hence grown in tubs is still often maintained by those who still recommend that they should be grown in pots or tubs. This has given rise to two conflicting views about either feeding them well or that they flower best when root-bound. However, if the pots or tubs are not protected in winter, like most plants the roots are more vulnerable to frost.

In general agapanthus require a light free draining soil in full sun. They will not flower in shade, so clearly require some ultraviolet light to encourage flowering. Grown under glass or polythene the flowers are a much paler colour than when grown in the open air. In cold wet heavy soil the roots of most species can and often will simply rot off in winter. Some forms of A. inapertus may be more tolerant of such conditions. In general most species of agapanthus do not require particularly rich growing conditions, which is just as well as my light free-draining soil is shallow over dolerite with little mineral content apart from iron, devoid of phosphate and with little organic matter and nutrients,. The vast majority of well over 200 forms of agapanthus that I grow have grown well in such conditions, with little sign of deterioration even after clumping for a decade or more. Probably only about half a dozen have deteriorated significantly and clearly needed some nutrition. However, plants that have been micro-propagated, which is most that are readily available nowadays, are different. They have been probably overfed from the start and thus if suddenly exposed to poor growing conditions will perform poorly, so they do need good conditions to perform adequately.

Perhaps surprisingly for drought resistant plants, agapanthus seed does not remain viable for long which is almost certainly due to dessication if kept in dry condition. It is thus best sown immediately when ripe. The seed does not seem to be adversely affected by cold conditions as the first year that I discovered copious quantities of self sown seedlings was after the first really cold winter for many years with several nights of frost of about
-12°C or even lower. Unfortunately most got weeded out inadvertently along with the subsequent more rampant weed growth. However, left to their own devices agapanthus will readily naturalise, especially near the sea and so are clearly well suited to coastal gardens.

In general the deciduous plants are hardier than the evergreen species A. praecox, which tend to have their leaves killed with temperatures below about –8°C. The leaves quickly resemble boiled spinach, though the leaves will re-grow again quickly in spring unless the basal shoot of the leaves is also killed back, which usually requires somewhat lower temperatures or a period under snow. The rhizomes above or even below the surface can be killed back by prolonged low temperatures. However, new buds will usually break from below the rhizomes and new leaves will eventually appear in late spring. If only a few such live growths appear in a large clump, it would be best to lift the whole clump and divide out the live pieces and replant them.

In the last decade, agapanthus seem to have finally gained wider recognition as hardy plants in the British Isles, spurred on by their ability to withstand drought and their more ready availability through micro-propagation. Whilst there is no accounting for taste or judgement many plants that have been micro-propagated and marketed are, to put it tactfully, undistinguished, and a few are less hardy forms of A. praecox. The choice is almost infinite given the proliferation of named cultivars in the last few years, though many would be difficult to distinguish from one another. The only reasonable advice to obtaining agapanthus is to buy plants in flower that you like.

An edited extract from an article first published in the Half Hardy Group Newsletter

© Copyright for this article: Gary Dunlop

This article was taken from a copy of Cornucopia that was published in 2014. You could be reading these articles as they are published to a national audience, by subscribing to Cornucopia.

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