long term performance the plantsman

8/2/2019 Long Term Performance the Plantsman

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GARDENERS ARE well awarethat herbaceous perennialspresent awide range offorms and behaviours, and that thereis considerable variation in their long-term performance. As someone whohas been a commercial grower, adesigner working in both privategardens and public landscapes, anda keen gardener, I have always beenfascinated by this. I chose the studyof herbaceous perennials foe adoctoral research project which Icompleted with the LandscapeDepartment of the University ofSheffield a few years ago. I also under-took further research in 2009-10 aspart of an EU-funded project.

The projectHere I present my findings from thislatter research project, which focusedon long-term plant performance.The overall project was aimed ataddressing cost-effective managementof public spaces, My particularresearch, however, is of relevance toprivate gardeners just as much asthelandscape and nursery industries - ittook the form of valuating the long-term performance of ornamentalherbaceous plants using aquestionnaire-based practitionersurvey. By performance I meanissues relating to the establishmentand long-term growth of plants ingarden conditions, and whether they

are likely to spread or to diminisawith time.

When I started my PhD researchI was hoping to be able to developcoherent system of categorizationfor herbaceous perennials - thisproved illusory. Instead, I realizedthat there were several gradientso fmorphology (often referred to a sarchitecture) and performance.These interacted to create somegroups, fuzzy groups, but groupsnevertheless. In the end I decidedthat the best way of thinking aboutherbaceous plants was throughconcentrating on a number ofk e yperformance indicators, whichcanoften be guessed at from an initial

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PlantsmanA c h i / l e a c u l t i v a r s a re o f t e n r eg a r de d a s s h o r t - l iv sdin g a rd e n s . m a in ly b e c a u se th e s p r ea d in g c lu m p sl a il lo m a i n t a in a c o r e o f g ro w t hlookat plant morphology, but whichcanonly really be reliably knownfromthe experiences of gardenersgrowingand observing over time.Tillswas the rationale behind using aquestionnaire to gather data ongardeners'experience oflong-termperformance.I have grown a number of

perennialswhich did not appear tob e perennial. In discussing this withothergardeners who have had thesameexperience, I made theexploration of longevity a key parto f the research. Indeed, I believe itis keyto understanding wider issuesofplantperformance. Herbaceousplantshave long been classified asannuals,biennials and perennials.Thedefinition of perennial as 'aplantlasting longer than two years'(Griffiths1992) iswidely accepted.llhatnot everyone agrees isillustratedby Graham StuartThomaswho frequendyuses thetermsshort-lived' or 'long-lived'(Thomas1976). Lifespan has actuallyb e e n little researched; work done atWeihenstephan in Germany beingdiemost systematic (Hansen &Stahl1 9 9 3 ) . It ismy contention that thefailureo address this fundamentalissues a serious weakness in thelanguageof horticulture.Performance indicatorslurygardener can no doubt listseveralerennials whose longevityt h e y would regard as 'short'. Amongcurrentlyfashionable plants, twostandout: Knau ti a macedon ica and& h i n a c e a . The behaviour of thef o r m e r inseeeling over awide area inmanyardens illustrates its lack oflongevitys not really a problem, butalsopoints us towards another keyaspectoflong-term gardenperformance- that of self-seeding.

Echinacea presents a particular problemfor gardeners as it isundergoingmuch adventurous breeding workirivolving interspecific hybridizationand iswidely commercially available.It isgenerally accepted to be short-lived, yet there are no indications inany reference sources as tohow short-lived, or what factors may influencelongevity. In talking to growers inthe US it is apparent that longevityin the wild is limited - it mayvaryconsiderably depending on condit-ions and it varies between species.

A key part of herbaceous plantperformance ishow effectively aplant will spread. Most speciesspread only slowly, some not at all.However, most gardeners can nameseveral species which spread soaggressively as to be frequently seenas a problem: two 'notorious'examples, being Eupho rb i a c ypar is si a sand Lysimachia punctata. Havingsome concept of spread is vital foranyone setting out new plantings,particularly in the design profession,but it ispoorly articulated in gardenreference books, and is frequentlynot actually given: Rice (2006) doesnot, whereas Thomas (1976) does.Hitchrnough (2003) is one of thefew who does address the issue,usefully discussing broad categoriesof herbaceous spread in a volumeaimed at the landscape profession.

Competition is clearly related todegree of spread, and is an issuemany gardeners accept ashighlyrelevant. Geranium x oxonianum'Claridge Druce', for example, beingfrequently seen as highly competitive- a good thing for ground cover ifthis iswanted, but possiblyproblematic in a small border. Inecological science' competition' hasa precise meaning, related to theability of aplant to succeed at theexpense of others, and to be able toeffectively utilize high levels ofresources more effectively than

others (Grime 2001).Two other performance issues

are speed of establishment and self-seeding. Both are recognizedanecdotally by many gardeners buthave never been systematicallyexplored, although Thomas (1976)and Gerritsen &Oudolf (2000make frequent references to bothcharacteristics. Pfalzner- Thomsen(1995) is one of the few with anykind of systematic exploration ofself-seeding in garden conditions.

Plant trialling, as for examplecarried out by the RHS, fails toaddress many of these issues. This ispartly because the time period (amaximum of three years) is not longenough for their evaluation andpartly because there isno agreedframework for understanding long-term performance issues. Indeed,they have never even been formallyarticulated. Yet, any informaldiscussion with gardeners, amateuror professional, is full of anecdotalmaterial about these very issues -hence my questionnaire.The surveyI made contact with a number oforganisations who put notices intheir journals asking for volunteers:the RHS, the Hardy Plant Societyand the Professional GardenersGuild. Volunteers were also soughtthrough emailing nurseriesspecializing in perennials (selectedfrom the R HS P la nt F in de r) andlarger private gardens open to thepublic on a regular basis (selectedfrom the Good Gar d en s Gu ide ) .

Volunteers were then requestedto select around 20 plants from alistof 96 fa.rfilling in data. The 96 werethe species I had made seasonalobservations of during my PhDresearch. They largely reflected therange of herbaceous perennialspopular in contemporary gardendesign (including a few grasses), > -

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with a stress on robust plants whichmight be expected to survive in low-maintenance situations. Excludedwere taxa such as As t er nov i- belg ii andDelphinium cultivars which are partof an older flora of perennials notedfor their high-maintenance needs.

The questionnaire asked respond-ents to score each of the 20 speciesthey had chosen on five criteria, byticking boxes (see table below).Respondents also gave details of theirgarden conditions, although in theend there were not enough to makeany use of these details . In actualfact, I would argue that the long-term performance issues I addressare driven by genetic traits and soenvironmental effects (e.g. garden

microclimate and soil type) have onlya limited impact. In addition, it iswell-established in plant ecology thatmost herbaceous perennials are'generalists' i.e. they thrive over awiderange of conditions (Grime 2001).Ihad 66 responses, from all over

the UK, overwhelmingly fromexperienced amateur gardeners, witharound a third professionallyinvolved in horticulture (designers,gardeners, nursery owners). Somewere in their 80s or 90s, withdecades of experience in growingsome of the plants on the list - it wasa very special feeling to be able tosystematically gather informationfrom such venerable gardeners.

Once the results were in, rTHE 5 CRITERIA AND SCORES USED IN THE QUESTIONNAIRELongevity ~L(mg.n table 'oppGsite)

1 vel)' sho r t - l ived , rarelymore than 3 yar-s2 short - lived,3--5years3 medium-liv:ed,plantsmay live 5 years or mo r e , but suddenly disappear4 long-lived,ptants appear to survive fo r ever

Vegetative spread (VS in table opposite)1 not spreading, staying in same place2 s10wlyexpanding dump3 stromglyexpanding clump4 spreading through occas iona l runners5 spreading strongly thnlUgh extensive runners6 discontinuous s pr ea d ; i .e , spreading ou twa r d s but o l d e r (1-2-year-old)

growthdymg7 as 6, but mor e vigorouslyCompetitwenes~ ~ C 0 1 i l i l . p . in table oppo s i t e )1 vel)' readily overwhelmed by neighbours or weeds

2 readilyoverwhelmed, but with some ability to survivecompet i t ion3 moderately robust, with ability to survivecompetition4 moderately spreading, ability to ShlPpFSSr infilnaee ne i ghbou r s ,

or resist weed encroachm.ent5 characteristically aggressivelyspreading, suppressing or heavi lyin.filtratingneighbours

Speed of establishment (SoE [lQ "alDIeopposite)1 slow,acceptableplant sizereached injyears or longer afterplancing2 moderate, acceptable plant sizereached in 2 years after planting3 fast,acceptable plant size reached in first year after planting

Spread by self-seeding (S-SII1table opp@site)I neverself-seeds2 rarelyself-seeds, or seedlings rarely reach maturity3 moderate self-seeding4 extensive, e v en n u is an c e, levelof self-seeding

analysed data for al l taxa where therewere more than ten responses, thenaveraged out the responses. I alsoundertook a standard deviation testwhich was useful for indicating thevariation in reporting of the variousperformance indicators. In the table(opposite, plOI) the means for theindicators are given. This numberdoes not indicate the value of theindicator itself, but the level ofreporting of the indicator, e.g. a valueof 3 .5 for longevity does not indicatethat the plant is long-lived but that alarge number of respondentsreported it to be so.LongevityThis is a key performance indicatorfor planning plantings on any scale.As can be seen from the tableopposite there is wide variationamong the perennials studied. Asmight be expected, respondentsreported that most 'perennials'are indeed just that.

What is interesting, though, arethose which are reported as being'less perennial' . In some cases (e.g.Di ct amnu s a lb u s) this may be becausethe plants are slow to establish andare therefore easily lost in the firstfew years; in others molluscpredation may affect perceivedlifespan (e.g.Aster x frikartii 'Monch ' )or lack of hardiness, as in Crocosmiataxa, or Aneman the l e I e sson iana .Thereare also those which spread clonally,but in such away as to make themvery vulnerable - chiefly throughfailure to maintain core growthunder the conditions of standardgarden management (e.g. Achilleataxa, Heuchera m ic ran tha hybridsand Monarda hybrids).

However, Ielieve'that there isanother category which is importantto recognize with a new name -'short-lived perennials'. These a r ethose species which are not strictlyspeaking donal, but form tight, )0

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ANSOF LEVEL OF REPORTING OF INDICATOR VALUES (FIGS. IN BRACKETS ARE lIIAX. SCORES POSSIBLE)VS(7) CO~.~ SoEG) S-S(4 )

2 . 9 2 . 11 . 9 2 . 02 . 6 2 . 12 . 6 2 . 22 . 6 2 . 41 . 9 1 . 62 . 5 2 . 12 . 2 2 . 42 . 7 1 . 73 . 1 1 . 7lA 2 .12 5 2 . 32 . 4 2 . 01 .@ ]'82 . 3 1 91 .7 1 f . 52 . 6 2 . 22 . 4 l 2 . 12 . 2 1 . 93 J : . l 2 . 52 . 5 2 . 12 . 7 M2 . 8 2 . 12 . 4 - [ , 91 . 6 t21 . 5 2 .02 . 4 2 .14 . 4 2 . 61 . 7 1 . 83 . 7 2 .22 . 4 2 . 12 . 4 2 . 23 .0 2 .32 . 0 2 . 51 . 7 1 . 82 . 3 2 .23 . 2 2 . 53 .3 2 . 41 . 8 1 . 82 . 0 2 .32 . 4 2 . 42 .7 1 . 91 . 8 2 . 22 . 4 2 . 02 . 3 1 . 91 . 9 2 .13 . 6 2 . 42 . 8 2.3 '4 . 3 2 . 22 . 6 2. 135 2 . 4z . s 2 . 52 3 2 . 23 . 7 ~ . 34. 1 2 . 53 . 3 2 . 52 . 6 2 . 22 . 8 2 .22 . 4 2 . 32 . 4 2 .42 . 4 n2 . 5 2 . : 01 . 9 1 . 92 . 3 2 .1


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non-spreading clumps (e.g.Aquzlegiavulgaris) or form no clonal growthwhatsoever tKnau tia macedon ica ) .These are plants ofunstable habitatswhere investment in clonal growth isnot worthwhile, but investment inseed is. We a U know how wellAqui le g ia v u lga ri s seeds around inalmost any garden.

What is worrying is how manyof these short lifespan species arecurrently among the most widelypromoted garden centre perennials:Achillea, Ecb inacea and Heucbera . Thefailure to recognize longevity as ahighly variable issue in the referenceliterature, let alone on plant labels,leads to frequent disappointmentamong the gardening public.Vegetative spread andcompetitivenessDegree of vegetative spreadproduced the least amount ofagreement among respondents,partly because of the problems ofdesigning a meaningful numericalscale to express it. There was clearagreement, though, on the followinglist of species with a highly effectiveability to spread vegetatively throughquesting ramets (aramet ismaterial,derived from either roots or shoots,capable of becoming an independentplant through natural processes):

Acan th u s mo ll isAnemone x hybr idaCentaurea montanaEuphorbia cyparissiasFilipendula rubraGeranium x oxonianumLys imachia detbroidesMac /ea ya co rda taMonarda hybridsPers icaria amplexicaulisPersicaria bistorta 'Superba'Phlomis russ e lianaThere is a clear link with

competitiveness. In some cases thebehaviour of these plants is seen as aproblem - the runners of Euphorbia

cyparissias attracted much venom inthe 'comments' section of thequestionnaire! However, thisnegative attitude is not shared by allgardeners; those more interested inlow-maintenance or naturalisticapproaches may welcome this abilityto occupy space.

Competitiveness is an indicationof those species with the moststaying power. These are immenselyuseful for situations where regularmaintenance is difficult (e.g. slopes),or in wild garden areas, or wheremaintenance may be erratic orunskilled, as in community gardens.Common sense suggests that theyare not appropriate for combiningwith slower-growing or smaller plants.

The means of spreading varies,which may impact on how the plantis used in the garden. Some form aclump, with all edges advancingequally, such es A ca nt bu s m o ll is andGeranium x oxonianum (ecologists callthis phalanx spread). Otherseventually form dumps but throughunderground ramets (dubbedguerrilla spread), such asEuphorbiacyparissias, Lys imach ia c! e th ro ides ,Macleaya co-rda taandPers icar iabistorta. There is an importantdistinction to be made here. In thewild these guerilla-spreading speciesgenerally intermingle with othervegetation as competition, especiallyfrom grasses, prevents them formingsolid clumps as they generally do inthe low-competition environment ofthe garden. Those of us who haveexperimented with denser, morenaturalistic plantings have foundthat it is possible to have these andother guerrilla spreaders intermingling.That they are strong spreaders doesnot necessarily translate intostrongly competitive behaviour.Speed of establislunentGardeners are often aware thatcertain plants have a reputation for

being slow to establish, butoncethere are there for ever.An exampleisAnemone x hybr idz w h ic h c a n b eamong the most long-livedofa n yherbaceous plant. The tableindicates that there isa categoryfplants which typically performnthis way. It isknown that semeofthese species are very long-livednthe wild, but spend their tUste wyears building up root mass(Kingsbury 2008) - e.g.B a p t i s i 4australis. Others are evergreen Fsemi-evergreen, such asH e l l e b o r wand Liriope. It iswell establishsddaevergreen foliage or other physicallytough foliage is 'expensive'forplannto grow, in terms ofresourceallocation (Grime 2001).

These species are notablefonforming very stable clumps,eitherforming an exclusive groundG o v e r(aswith Liriope) or tight, long-livedclumps (as with Baptisi(t).lf c a r e a nbe taken to avoid them beingoverwhelmed when young,t h elongevity of these plants makesi h i searly effort a good investment.Self-seedingThis isan aspect ofgardeningW h i c hmany of us take great joy in - thefeeling that ifa desired plantpropagates itself this isagood h i n gand that it is happy with ourg a r d e ~Self-seeding is seen positivelyb ymany contemporary designandhorticulture practitioners whoregard it as part of a healthyecological dynamic and naturalisticaesthetic. In some cases,however,the seedlings may become toom u c hof a good thing and the plantgetsrelegated to weed status. Commen~on the questionnaire indicateiilthatformany gardeners A ! C h e m i l l a m o l l ~has achieved exactly t hi s s ta tu s .

Ulllike vegetative spread, self-seeding is very difficult to predict,and may relate to soil type. Self-seeding of garden perennials may

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Plantsmanalsobelimited by genetic factors; agreatmany garden plants arepropagatedclonally or from a veryreducedgenepool which may reducet h e i r ability to set viable seed. It is~sopossible that species originatingin continental climates (e.g. NorthAmericanperennials which form al a r g e contingent of our garden flora)d o not get enough late-seasonw a r m t h to fully ripen seed.The data shows that there is a

\ \~derange of competitivenessamonghe most frequently self-swing species. Whether a self->owingpecies has the capacity tobecomeaweed depends very mucho n circumstances and habit.REFERENCESGerritsen, H &Oudolf, P ( 20 00 )D r e a m P l a n t s f o r P l a n t i n g t h e N a tu r a lG a r d e n .Timber Press, OregonGr i ff i th s , M (1992) T h e RoyalH o r t ic u l t u r a l S o c i e ty I n d ex o f G a r de nP l a n t s . Macmillan,LondonGrime,]P ( 2001) P l a n t S t r a t e g ie s ,V e g e ta t io n P r o c e s s es a n d E c o s y s t e m' P r o p m i e s .John Wiley, ChichesterHansen ,R &S ta hl, F (1993)P m n n i a l s a n d t h e i r G a r d e n H a b i t a t s .CambridgeUniversity Press,CambridgeHitchmough,] ( 2003) Herbaceousperennials.n: Hitchmough,] &F ie ld ho us e, K ( ed s) P l a n t U s e rH a n d b o o k ,a G u i d e t o E f f e c ti v eS p e c i f y i n g .Blackwell,OxfordK ing sb u ry , N ] (2008)Ani n v e s t ig a t i o n i n to t h e p e r fo r m a n c e o fi p e c ie sn e c o l o g ic a l ly b a s e d o r n a m e n t a lb e r b a c e o u s e ge t a t i o n , w i t h p a r t i c u la rr e fe r e n c eo c o m p e t it io n i n p r o d u c t i veenvironments .Unpublished doctoralt h e s i s , Universityof SheffieldPHilzner-Thomsen, G (1995)SelbstaussamendeStauden. GartenP r a x i s 3 : 14 - -20!Rice,G (ed.) ( 2006) R o y a lH o r t ic u lt u r a l S o c ie t y E n c yc l o p e d ia o fP e r e n n i a l J . Dorling Kindersley,LondonT h o m a s , G S (1976)P e r e n n i a lG a r d e n P l a n t s . 1M Dent &SonsLtd,London

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Spreaders such as Geranium xo xo ni an um a ndA !c h em il la m o ll is arefar more problematic than thosespecies which form only a very tightnon-spreading clump, such Aquilegiavulgaris and Geran ium sy lva ti cum . Inthe case of short-lived species suchas Knau ti a macedon ica and Aquz legiavulgaris the readiness to self-sow canbe seen as avaluable aspect of theplant, ensuring their continuedpresence in the garden. The fact thatEcb inacea purpurea self-sows onlyinfrequently will no doubt countagainst its long-term popularity.ConclusionsThe traditional division of non-woody plants into three categories ofannual, biennial and perennial lookspretty threadbare. The questionnaireresults plus other evidence haspersuaded me that it is morerealistic, and helpful to gardeners,to think in terms of ag radient. Inaddition, there is a key distinctionbetween clonal perennials and non-clonal perennials, biennials (andother monocarps) and annuals. Evenamong the clonal perennials there isa tendency for some to be highlyspatially mobile (e.g. some Achil leaand Monarch. taxa) and therefore tobe short-lived in practice. Amongthe non-clonal perennials Ibelievethat there is a large group of short-lived species which readily self-sow,if certain other factors arefavourable. There is no doubt thatplants such as Knaut ia macedonicaand E c h i n a c e a purpurea are of greatornamental value, but we should beaware of their limitations and beprepared to educate the wider publicwith this knowledge.

Long-lived, robust, spreading, andindeed competitive, perennials havetheir place in the garden, especiallywith increasing numbers of.gardeners seeking to experimentwith naturalistic designs. On moist

and fertile soils these plants are aboon, as only they can hope tocompete with aggressive weedyspecies where levels of maintenanceare reduced.

There is another reason for payingmore attention to plant competitive-ness and increasing our knowledgeof these plants. As cuts in publicservices bite, it is highly likely thatkeen gardeners will become moreinvolved in voluntary management ofpublic spaces or conununity gardenprojects; more ornamental 'lovablethugs' are just what these places need.In addition to strongly-spreadingspecies there are species withconsiderable staying power overtime, but which do not spread, or atleast not vigorously. These can beexpected to long-term elements inplanting, but there is a trade-off-that they are slow to establish andvulnerable to competition orpredation in their early years.

At the beginning Imentionedthat an initial look at a plant mightprovide indications asto its long-term performance. Ibelieve that inmany cases we can 'read' the plant,and have in fact successfully includedthis approach into workshops whichIhave run for designers, thelandscape profession and amateurgardeners. The number oflength oframets can give strong clues as topotential spreading ability, theirabsence or very tight integrationstrongly indicates a potentially short-lived perennial etc. To make suchobservations and to be able to makepredictions from them canpotentially do much to enrich ourknowledge of the plants we grow andimprove our ability to use themeffectively in the garden.NOEL KINGSBURY is a writerand designer. He has also run anursery and designed publicplantings in Bristol

long term performance the plantsman

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