Why it’s time to di­vide and conquer

Belfast Telegraph - Weekend - - GARDENING - BY DIARMUID GAVIN

We’ve been dig­ging up the gar­den we cre­ated at Dun­drum town cen­tre (while plan­ning some fu­ture ex­cite­ment in its place) and I’ve been amazed at the growth of the plants in a cou­ple of sea­sons, es­pe­cially the herba­ceous peren­ni­als.

Most of the plant­ing com­prised colour­ful species, us­ing peren­ni­als to add height and in­ter­est to the plot. By their na­ture th­ese plants be­gin to dieback at this time of year. Be­cause they don’t pro­duce woody stems, the flower and fo­liage will wither away while the root sys­tem takes a rest over the late au­tumn and win­ter.

Herba­ceous colour pro­vides most of the in­ter­est in con­tem­po­rary flow­er­ing gar­dens. In my youth I spent some fan­tas­tic years train­ing among won­der­ful gar­den­ers in Dublin’s Botanic Gar­dens. One of my most vivid mem­o­ries from those days was its long herba­ceous bor­der.

This is a gar­den fea­ture that over­whelm­ingly re­lies on herba­ceous-type plants for in­ter­est (with oc­ca­sional bulbs, an­nu­als and bi­en­ni­als adding to the de­light). I was en­chanted by its sea­sonal de­vel­op­ment — al­most bare dur­ing mid­win­ter and then, just six months later, a huge flour­ish of colour.

The win­ter pe­riod was when fo­liage and flow­ers had died off and the plants needed tend­ing. This could in­volve dig­ging out the roots of bindweed or couch grass, or feed­ing with a mulch of well-rot­ted ma­nure. But my favourite herba­ceous job was di­vid­ing the over­grown spec­i­mens, which we are now be­gin­ning to do at the Dun­drum plan­ta­tion.

As leaves start to fall and au­tumn draws in, Oc­to­ber makes me pre­pare for more prop­a­ga­tion. It’s a great time to plan and re­view what worked best this year in the gar­den. And if there’s a herba­ceous peren­nial that did re­ally well and you’d like to see more of it around the gar­den, the best way to achieve this is by di­vid­ing up the plant into smaller plantlets and re­plant­ing. This is called lift­ing and divi­sion and it is one of the eas­i­est ways to prop­a­gate herba­ceous plants.

Divi­sion is also nec­es­sary ev­ery few years to keep some herba­ceous peren­ni­als fresh. He­le­ni­ums and Michael­mas daisies tend to grow out in con­cen­tric cir­cles, leav­ing a woody old base at the cen­tre — think of a peb­ble send­ing rip­ples through a pond. The outer rip­ples are the fresh growth you want to har­vest, while dis­card­ing the cen­tral woody base. Ideally, you’ll lift and di­vide th­ese plants ev­ery two to three years. Shasta daisies and phlox will ben­e­fit from an­nual divi­sion while hostas, pe­onies and daylilies will hap­pily clump along, per­form­ing well with­out the need to dis­turb them.

So how do you go about it? The first rule is about tim­ing: early-flow­er­ing peren­ni­als are best di­vided in au­tumn, late-flow­er­ing peren­ni­als in spring. So you can leave he­le­ni­ums, asters, eu­pa­to­rium, rud­beck­ias and grasses to keep flow­er­ing undis­turbed and at­tack them next spring. But the re­al­ity of any tim­ing rule is that you’ ll prob­a­bly tackle the job when you have spare time or when the weather is good enough. Some great can­di­dates for divi­sion now are prim­u­las, brun­neras, hardy gera­ni­ums and heucheras.

Dig up the plant you want to di­vide and shake off the loose earth so you can see what you’re op­er­at­ing on. Plants with a fi­brous root sys­tem, like hardy gera­ni­ums and astilbes, will break apart into plantlets quite eas­ily. Oth­ers will re­quire a bit more tug­ging — two gar­den forks back to back in the cen­tre of the plant is a good way to tease apart thicker clumps like daylilies. The sharp end of a spade is ex­cel­lent for hack­ing through tough roots like hostas and aga­pan­thus. Gen­er­ally, plants with thick fleshy tap roots — Ori­en­tal pop­pies, lupins, acan­thus — aren’t so easy to di­vide and are bet­ter prop­a­gated via root cut­tings.

You can plant your di­vi­sions in situ, cre­at­ing drifts of favourite peren­ni­als through the borders, but keep them well wa­tered while they es­tab­lish, and add com­post and fer­tiliser to the plant­ing hole. You can also in­di­vid­u­ally pot up the smaller plants to bulk up be­fore plant­ing out next year.

HAR­VEST TIME: He­le­ni­ums and Michael­mas daisies (right) should be di­vided ev­ery two to three years for re­plant­ing, while Shasta daisies (in­set) ben­e­fit from an­nual divi­sion

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