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Many gardeners are frustrated by the limited amount of information given in plantreference books, particularly about the long-term performance of herbaceousperennials. We have all had the experience of plants which are described asperennials but which die after a couple of years, or of plants that take ages toestablish, or which seed around to an extent which can make us regret ever havingbought them.

Those who use plants professionally – designers and landscape architects – findthis especially problematic. Indeed lack of knowledge about long-term performancemay actively discourage many professionals from using herbaceous perennials.

Go to an HPS meeting, however, or gather together any group of gardeners, andthere is a buzz of information being exchanged, much of it about just thesequestions of long-term performance… “spreads like crazy, doesn’t say that on thelabel”, “always dies after three years”, “it self-seeds in my neighbour’s garden butnever mine”. It was to try to gather together some of the information from this‘anecdotal cloud’ that I applied for funding from an EU-supported project which theDepartment of Landscape at the University of Sheffield had joined. The projectconcerned was an ‘MP4’, where practitioners in a particular field compare and

Gathering gardeners’ knowledgeNoel Kingsbury

Fig. 1 Knautia macedonica is popular in all its various colour forms. It is reported as relativelyshort-lived, but compensates through frequent self-seeding.

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contrast best practice across nationalboundaries; this particular project wasdesigned to look at the cost-effectiveness ofthe management of public space. My proposalwas that I should design a simplequestionnaire on long-term plant performanceand persuade experienced gardeners to fill itin, in order to gain more insight into some keyquestions about common perennials.

A note in The Hardy Plant [Vol. 30 No. 1],The Garden, and the newsletter of theProfessional Gardeners Guild resulted in atotal of 66 completed questionnaires – ofthese 23 were from HPS members. Judgingfrom the replies and from covering letters,many were very experienced gardeners – itfelt marvellous to be able to tap into theknowledge of people with 20 or even 30years’ experience of growing particularspecies. Many participants said how muchthey enjoyed taking part, as it made them thinkabout their plants in a new way.

Participants were asked to select plantsfrom a list of nearly 100 perennials – allplants about which I had already collected aconsiderable amounts of data from research Ihad conducted doing a PhD in the Land-scapeDepartment at Sheffield University. Of theplant species and varieties which participantschose to answer questions on, 62 had at leastten responses, which I judged was enoughdata to analyse. The overall picture confirmsand illustrates something to which I havedevoted much thought over the years – thatherbaceous perennials fall into some definite,but overlapping and cross-cutting categories.More useful knowledge for the gardener thancategories, however, are the differences in thevarious performance criteria.

Fig. 2 Sedum (Herbstfreude Group)‘Herbstfreude’ comes out as a reliablylong-lived, and relatively trouble-free plant.

Fig. 3 Echinacea purpurea and its varioushybrids is now a very popular plant.Respondents however gave it the lowestrating for longevity, and a low rating forcompetitive ability. Sometimes short-lived species are reliable self-seeders –but not this one!

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LongevitySome ‘perennials’ really do die very quickly –in everyone’s gardens, not just yours! The datashowed that there is a gradient of longevity –from the ephemeral to those species which BobBrown describes as ‘bomb-proof’ (certaingeraniums, hostas – despite the slugs, Acanthusmollis and Miscanthus grasses). A great manyothers which would also appear to be long-lived but occasionally fail. Then there are thosewhich definitely appear to be inherently short-lived: some of the worst are varieties ofEchinacea, Achillea, Heuchera and Monarda,There are also those which are short-lived butin many gardens continue to reproducethemselves with seedlings (albeit sometimestoo enthusiastically), e.g. Knautia macedonica(fig. 1) and Aquilegia vulgaris.

Looking at the data, my conclusion is thatwe need to distinguish between perennialswhich spread vegetatively, forming clumpscomposed of large numbers of shoots each

with their own roots, and therefore potentiallyan independent plant, and those which do not.The latter may include many, such as theborder sedums (fig. 2) and Salvia x superbaand relatives, which may be long-lived butwhich are always be vulnerable to damagebecause they do not form a constantlyspreading clump. Those which are definitelyshort-lived are nearly always distinguishableby the single connection between their rootsand the top growth. Consequently, I believethat anyone examining an unfamiliar perennialfor the first time could predict its longevityfrom paying close attention to the way theroots and shoots connect.

Learning to recognise the potentiallongevity of perennials is important, as thenursery industry currently seems to favour

Fig. 4 Euphorbia cyparissias is notorious asan aggressive spreader, but is easily out-competed by taller plants. Respondentsin fact reported wide variations in howextensively it spread; they either foundthe habit useful or regretted ever havingintroduced it to their gardens.

Fig. 5 Lunaria rediviva. Survey participantsreported this to be moderately, but notreliably long-lived, and modestly self-seeding.

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producing new varieties from several generawhich seem to be inherently short-lived –hybrids of Echinacea (fig. 3) are a good casein point. It is, of course, in the interests of thenursery industry to produce short-lived plants– but it would be nice to be given a clearer andmore honest assessment of expected longevityon the label! For those interested in genuinelongevity, and particularly those who areresponsible for spending public money, this isan area of key interest. In my final report Icriticise the nursery industry for not puttingenough effort into developing and promotingnew varieties of reliably long-lived and robustperennials. It would also help greatly if we allrecognised a new category – short-livedperennials.

Vegetative spreadFollowing on from what has just been said, we can expect perennials to spread atdifferent rates. Ecologists use two rather military terms to describe the ways inwhich spreading species achieve their aims: phalanx, where the plant movesoutwards on a solid front and guerrilla, where odd runners are sent out overrelatively long distances. The latter approach, familiar to many of us fromEuphorbia cyparissias (fig. 4), can be seen either as a nuisance or a useful way offilling space – depending on one’s gardening style! The research has helped toclarify which popular perennials use which type of spread. It also confirmed thelink between the effective reach of vegetative spread and two other factors:longevity and a relative lack of self-seeding ability. There is a clear trade-off here –a plant which spreads effectively through runners or rhizomes tends not to self-seed. The exception is Geranium x oxonianum, the variety ‘Claridge Druce’ aspectacular example in the experience of several research participants, as it runsand can self-seed profusely.

Sometimes there appears to be a wide divergence in experience. Some gardeners,for example, report spreading by runners in Centaurea montana, others do not;quite possibly there are different forms in cultivation which behave differently,which we might expect from a species which has probably been introduced intocultivation several times over. This was another issue which came up several timesin the project – that there are differences in the level of genetic variation amongstgarden plants: named hybrids and cultivars are (or should be) identical, while

Fig. 6 Achillea (Galaxy Series)All achilleas were reported to berelatively short-lived, and uncompetitive,although experience would appear tovary widely, particularly with longevity

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species may be derived from asingle introduction and thusshow little variation, or frommultiple introductions, when wewould expect more variation.

CompetitivenessThe ability of a plant to competewith others in the garden isclearly related to its spreadingability. The following were thespecies which respondentsrecorded as being the most likelyto spread and smother neighbours:Lysimachia clethroides, Acanthusmollis, Persicaria bistorta‘Superba’, Geranium x oxonianumtypes, Macleaya cordata andEuphorbia cyparissias. Plantsmost likely to be smothered were

almost invariably non-spreaders and quiteoften short-lived too, such as Echinaceapurpurea. However, many species which seemreliably long-lived are not greatly competitive,such as Amsonia orientalis and Baptisiaaustralis.

Speed of establishmentMost perennials establish quickly, but not all,and in some cases reliably long-lived and/orrelatively competitive species may be slow toget going, and because of this may fail in theirfirst couple of years, either because ofcompetition or vulnerability to variousenvironmental stresses; examples are Amsoniaorientalis, Anemone x hybrida, Baptisiaaustralis, Helleborus x hybridus, Iris sibirica,and Liriope muscari. Evidence from othersources, both technical and anecdotal, indicatesthat what these plants are doing is investing in

Fig. 7 Persicaria amplexicaulis in the author’s garden, aspecies reported by participants in the study as stronglyspreading and reliably long-lived. Behind is pale blueCampanula lactiflora and Telekia speciosa, which werenot included in the study; the former would appear tobe a long-lived plant, the latter distinctly short-lived,both capable of moderate levels of self-seeding.

Fig. 8 Brunnera macrophylla was generallyreported to be long-lived andmoderately competitive. The specieswould appear to self-seed in manygardens; named cultivars appear to dothis less often.

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extensive root-systems in their early years; thishabit appears to be of benefit later, as many arenotably long-lived and resilient plants.

Self-seedingFor some gardeners this is a curse, eitherbecause soil types favour the germination ofevery seed which hits the ground, or becausethe tidier-minded do not appreciate so muchspontaneity; for others it is a blessing, as it canresult in the development of a dynamic andnatural-feeling planting. Where species tend tobe short-lived, such as Aquilegia vulgaris, it isimportant for their survival in the garden, but itmay be a nuisance if they are also spreadersthrough vegetative growth, as with Alchemillamollis and some of the more strongly-spreading geraniums. Some species, which arenot spreaders and have a physically quitenarrow profile, can self-seed extensively andcreate attractive mass effects as they do so, aswith Geranium sylvaticum, Lunaria rediviva (fig. 5) and Thalictrumaquilegiifolium. Few of us begrudge the extensive seedling production ofHelleborus x hybridus either.

This survey was also an interesting, although very limited, opportunity to assessthe popularity of perennials with experienced gardeners. The top five were, indescending order, were Helleborus x hybridus, Alchemilla mollis (viewed either asindispensable or hated for its seeding abilities), varieties of Crocosmia (althoughthere appears to be a huge variation in hardiness between different cultivars),varieties of Miscanthus sinensis and of Pulmonaria.

My experience with this project has convinced me that it is possible to gathertogether the extensive, but often very disparate, knowledge that gardeners have, anddraw useful conclusions from it. Such conclusions can then be useful forprofessional as well as amateur gardeners. I am very interested in carrying outfurther research using this methodology, though as ever that will depend onfunding, so I may well be appealing to your generosity in sharing your great fund ofknowledge and experience again.

NNNNooooeeeellll KKKKiiiinnnnggggssssbbbbuuuurrrryyyy is a teacher, lecturer, horticultural consultant and writer –about plants, gardens and the environment.

Fig. 9 Rudbeckia fulgida. A number ofdifferent forms of this species are incultivation, all appearing to be long-livedand with a moderatey spreading habit.One of those plants for which no onehad a bad word

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The ten plants most frequentlyreported as being short-lived (mostoften short-lived first)Echinacea purpurea and hybridsAchillea interspecific hybridsAquilegia vulgaris and cvs.Achillea millefolium cvs. (fig. 6)Heuchera micrantha and hybridsMonarda hybridsKnautia macedonica and cvs.Dictamnus albus and cv.Anemanthele lessonianaAster x frikartii ‘Mönch’

Plants always reported as beingreliably long-lived:Geranium x oxonianum typesHosta, various taxaGeranium sylvaticum cvs.Acanthus mollisLiriope muscari and cvs.Miscanthus sinensis and cvs.

The ten top spreaders byvegetative means (greatestspreading ability first):Euphorbia cyparissias and cvs.Macleaya cordataPersicaria bistorta ‘Superba’ (fig. 7)Persicaria amplexicaulis and cvs.Filipendula rubra and cvs.Lysimachia clethroidesMonarda hybridsAnemone x hybrida cvs.Geranium x oxonianum typesPhlomis russeliana

The ten species reported as beingthe slowest to establish (slowest toestablish first)Dictamnus albus and cvs.Baptisia australisAmsonia orientalisAnemone x hybrida and cvs.Geranium renardii and cvs.Helleborus x hybridusAster x frikartii ‘Mönch’Euphorbia polychroma and cvs,Liriope muscari and cvs.Iris sibirica cvs.

The ten species reported as beingthe most effective self-seeders (themost effective first) Aquilegia vulgaris and cvs.Alchemilla mollis Anemanthele lessonianaHelleborus x hybridusGeranium x oxonianum typesBrunnera macrophylla (fig. 8)Geranium pratense and cvs.Centaurea montana and cvs.Lunaria redivivaThalictrum aquilegiifolium and cvs

If you would like to contribute topossible future research, or you would like a copy of thefull report, please contact me via email –[email protected]


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