Verticordia in the Garden

Max Hewett

The late Max Hewett was the leader of ANPSA's Verticordia Study Group. Although this article was written in 1995, the information is still relevant for those wishing to grow Verticordia species. The article was first published in the Society's journal Australian Plants, Vol.18 No.145, December 1995.



Introduction

Except for a few tropical species which occur across the top of Australia and which to date have resisted establishment in the southern states, Verticordia is endemic to the south-western winter-wet corner of the continent. As might be expected, their introduction to areas with opposing weather patterns is not without problems. However, until comparatively recent times, very few species have been successfully established even in their own climatic region.

   Verticordia picta
   Verticordia picta.
Photo: Brian Walters

As with many other examples of Western Australia's outstanding flora, once thought to be difficult because of climatic variation, but now becoming well known in the summer-wet regions of eastern Australia, the growing of Verticordia may now be contemplated by those prepared to give that little extra thought and effort.

It has become evident that many parameters are common to both summer and winter-wet areas. Many species are now being grown successfully throughout Australia. With others, we have had only partial success but this will serve as a basis for more research into better long-term establishment.

Grafting treatment has also proved very worthwhile for some species which have shown sensitivity to soil-borne pathogens. More general commercial application will increase the popularity of these beautiful wildflowers, as they could then be grown without provision of special conditions.

Many cultural matters influence plant performance of species from Western Australia when grown in the eastern states, such as fertilising, time of planting in various climatic zones, response to dry winter and early spring conditions, especially in summer-wet areas, plant aspect, etc. Early research has been directed predominantly towards identification of the basic major hazards.

Major hazards in growing Western Australian plants, especially Verticordia

These hazards are recognised as root rot, collar rot and mildew, moulds etc. Chemical treatments may be appropriate at times but research to date has concentrated predominantly on the achievement of control by physical considerations.

  • Root rot of garden shrubs

    Root rot is destruction by soil borne pathogens which attack root structures. It results in the plant's inability to take up moisture and nutrients from the soil and has confronted gardeners from time immemorial. With specific attention to soil type and drainage, this hazard can be controlled reasonably well. It is a particular problem with some Verticordia species in summer-wet areas.

    The traditional gardening response has been to improve drainage conditions, and mounding of beds has certainly proved worthwhile. With some Verticordia, particularly in late summer when the soil is warm and moist, inadequate rate of drainage as well as the depth can be a significant factor. Compacting of soils over time, particularly with soils in the medium to heavy range, may be a problem. Initial planting procedures can be important and my recommendations are given in the table under 'Cultivation of Verticordia', below. Some species such as Verticordia chrysostachys var. pallida have made very good early growth in finely textured, well mounded loam but slow drainage speed has proved inadequate in late summer. Verticordia picta, is reliable in light sand or sand and gravel to a depth of about 30 cm over heavy base, but has been difficult to establish otherwise.

    A reasonable guide to preferred soil type may be assessed from observation of the initial root development of species at the propagation stage. Where first roots emerge predominantly horizontally or at least shallow, it is probable that the species will do well in heavy soils. Varieties of Verticordia huegelii in this category have adapted well in quite heavy clay loams. Where the first root development tends to be predominantly vertical, lighter soils have generally proved more appropriate.

    Some Verticordia species may develop a lignotuberous root system and are less troubled by problems of root rot. Verticordia chrysanthella is one such species which has done well in both light and heavy soils.

  • Collar rot of garden plants

    Collar rot is attack by soil-borne pathogens to the plant stems, at or near surface level. Destruction of the outer section of the stem (known as the cambium layer) results in the inability of the plant to transfer moisture or nutrients between the root system and the foliage. In summer-wet areas such as eastern Australia this hazard can be a major problem with many garden shrubs, especially many western plants such as Verticordia that have evolved in a summer dry climate.

    Verticordia grandiflora   
      
    Verticordia pritzelii   
    Top: Verticordia grandiflora.
    Bottom: Verticordia pritzelii.

    Photos: Brian Walters, Keith Townsend
      

    Factors effecting collar rot include mulching of the soil surface around the plant, watering methods and for Verticordia, in my opinion, potting mixes and plant dormancy. Of these, the surface condition of the soil is the more apparent difference between growing in summer-dry and summer-wet areas. In the west, the summer dry period, as well as extending well into autumn, is generally hotter, and the hazard of collar rot is reduced. This is the establishment period of young plants, and vegetative surface mulches created by leaf litter are an advantage in such areas.

    In summer-wet areas, vegetative mulches appear to be a source of collar rot attack. The adoption of more sterile surface conditions using gravel mulches or by permitting undisturbed natural weathering in the case of gravelly soils, has done much to alleviate this collar rot problem.

    Many Verticordia flower from late spring well into summer and before flowering they will respond favourably to summer rain or hand watering. Flowering is frequently followed by some degree of dormancy and the humid late-summer conditions which prevail in eastern areas coincides with this rest period. This can place collar rot susceptible species under additional stress.

    It has been observed with some species, in the higher range of susceptibility to collar rot attack, that failures have occurred due to the moisture-holding capacity of the potting mix used initially in the nursery stage. It has seemed that this has later contributed to collar rot problems in holding more moisture near the plant stems than is desirable during summer-wet conditions. My solution to this is given under the heading 'Planting Procedure' below.

    To maintain sterile surface conditions around planted specimens, it is sometimes necessary to clear the plant's own leaf litter away from plant stems should excessive summer leaf drop occur. Verticordia staminosa ssp. cylindracea var. erecta is one such species which, although generally quite hardy and reliable, can be vulnerable to attack under wet late-summer conditions. Growth response to wet weather throughout the year is good with dense leaf production. It is one of the earlier species to flower in dry conditions in early summer and when flowering has finished, heavy leaf drop can lead to collar rot attack.

    Hand watering can increase the risk of attack with some species. Verticordia have shown very good tenacity under hot and dry summer conditions and mature specimens, particularly in eastern Australia, have generally proved quite capable of surviving without such attention. An exception can arise where very shallow rooted species have been grown in light sandy soil and the entire root system is in danger of drying out. Watering should be maintained during the establishment stage should dry conditions prevail. In the cooler part of the year hand watering may safely be done throughout the day. When species are in flower it is best to water below the foliage to avoid flower damage. During hot weather water in early mornings so that excessive moisture is not retained around plant stems for long periods. Do not water late or overnight, when most collar rot problems start. It is also important that watering be done on occasions when the weather conditions later in the day could be expected to dry the surface quickly such as from wind, hot temperatures or low humidity. Trickle watering has sometimes been used; in light sandy beds it can be difficult to obtain adequate moisture distribution through the soil and spraying may be more appropriate.

    Mound specimens slightly at planting time, and form slight depressions between plants. As well as helping to throw excess water away from the vulnerable stem areas and thereby effect faster surface drying after rain, the depressions can also be useful in training water deeper into the soil where it may do more good. Such treatment furthermore tends to reduce general surface scour in heavy rain.

  • Mildews, moulds, etc.

    Fungal attack on the stems or leaves is a hazard when cultivating some plants, resulting in plant debilitation and, at times, death. This hazard can be more difficult to control than root and collar rot and grafting on to hardier rootstock does not avoid the problem. Attack appears to be related more to seasonal conditions than to geographical division into summer or winter-wet regions. On some plants the effects are relatively minor and may only cause temporary damage even if no counter measures are taken.

    Verticordia grandis   
    Verticordia grandis.
    Photo: Brian Walters
      

    For Verticordia, fungal attacks occur more frequently in summer-wet areas and in wetter than usual summer conditions in other areas. In summer-wet areas some of the yellow-flowered species are particularly susceptible in autumn to mildew attack, although when late summer weather patterns are drier than usual the problem is much less evident. Verticordia chrysanthella is such a species and although debilitation may be quite appreciable in some years, with defoliation, recovery may generally be expected later during winter and spring. It appears to be caused, not so much by the wet, late summer conditions to which the plant may have responded with lush new leader growth, but to the effect on such growth a little later in autumn, from widely-contrasting drier weather, and while night temperatures are still moderate. One approach is to do nothing and await natural recovery. Healthy new growth can be expected to return in several weeks with the advent of cooler and wetter conditions. You could lightly prune off the recent lush leader growth, thereby delaying the start of new seasonal development by a month or so. As a last resort chemical treatments with fungicides such as Mancozeb or Triforine can assist control. Relatively minor attacks may occur on a few of the pink-flowered species such as Verticordia piumosa or Verticordia monadelpha but these will grow out later as weather conditions become cooler and wetter.

    In near-coastal, summer-wet areas, Verticordia mitchelliana almost invariably suffers debilitation with serious leaf-drop in late summer. In inland districts the problem is rarely evident. The leaf-drop noted is usually rapid and comes at the end of a strong summer growth period during which the leaves have appeared almost succulent. The problem follows a change in weather pattern to cooler, less humid conditions and appears to start with fungal attack at leaf junctions with the stems The leaf drop is slightly less severe when the seasonal weather change is gradual rather than abrupt. Treatment with fungicides has failed.

    All three species in Verticordia Section chrysorrhoe, viz. V. nitens, V. aurea and V. patens are particularly susceptible to foliar fungal attack. For V.nitens it can be extremely debilitating leading to rapid total collapse of the specimen, and such loses are not restricted to summer-wet areas. The natural growth habit is to produce very tall, fast-growing but soft-wooded flower stems. These stems are very susceptible to attack, the first indication of which is a purplish discoloration of the new growth a few inches below the growing tip. The only counter seems to be early pruning of rapidly growing soft-wooded stems to induce multiple branching. The plant form is then changed to that of a multi-branched lower shrub, which although still susceptible to fungal attack, is considerably more tenacious. In summer-wet areas the fungal attack is generally still severe enough to present a debilitated appearance. Verticordia aurea and V. patens, although not so badly affected as the above, are still difficult species to maintain, especially in summer-wet areas. The fungal attack occurs predominantly on the new leaves and stems causing severe debilitation with stem purpling.

Planting procedure

Potting mixes are very different in texture, nutrient value and moisture holding capacity from the garden soils that will receive the plant. Preplanting preparation of Verticordia plants has been used to advantage for location compatability and to provide greater resistance to root and collar rotting pathogens. Harden the plant in a pot of soil similar to that of its intended location. For advanced purchased plants, they are first bare-rooted, any root coiling removed and then lightly pruned. After repotting they should be staged in favourable conditions until new vigorous growth develops. Some additional measures have been used to advantage. The soil is not pre-cultivated but rather left in the compacted state. This is important for heavy garden conditions. Use a minimum sized hole, water the plant well. Autumn planting is preferred so that subsequent additional watering is not required. The plant is then given a hard prune. Follow-up treatment is restricted to removal of leggy growth. Verticordia monadelpha, V. attenuata and V. pholidophylla have responded well to this treatment in heavy base soils.

Cultivation of Verticordia

The information in the following table is based on experience in the eastern Australian, summer-wet conditions.

Key to soil type: Note: Where more than one soil type is shown, they are listed in order of preference, with a suffix 'b' for the most preferred soil.
  • H: Heavy clay-loam.
  • M: Medium finely-textured loam.
  • L: Deep light sand.
  • G: Predominantly gravel, deep with loamy-sand matrix.
  • S: Sandstone parentage with high percentage of sandstone rubble.
  • HL: Heavy-loam base with sand mixed into top 18 cm (medium depth root development).
  • LM: Deep sand with medium loam mixed into top 18 cm (for deep root development).
Key to susceptibility to root rot, collar rot and to mould, etc.
  • nil: No problem recorded.
  • PI: Light attacks noted.
  • Pm: Moderate attacks.
  • Ps: Severe attacks noted.
Key to root stocks for grafted plants:
  • D: Darwinia citriodora
  • C: Chamelaucium uncinatum

Species Best Soil
Type
Root Rot Collar Rot Mould Grafted
On To
V. acerosa var. acerosaGb, L, HLnilnilPID, C
V. acerosa var. preissiiMb, HLnilnilnil 
V. albidaLbPlPmnilC
V. aereiflora     
V. amphigia     
V. apecta     
V. argentea     
V. attenuataGb, HLb, L, SnilnilnilC
V. aureaHLbnilPmPs 
V. auriculataLb, HLPmPmnil 
V. bifimbriataLbnilnilnil 
V. blepharophyllaGbnilnilnilD,C
V. brachypodaMb, HLb, HPIPInil 
V. brevifolia ssp. brevifoliaLbnilPmnil 
V. browniiHLb, LPmPIPID
V. capillaris     
V. carinata     
V. centipedaLb, HLnilPmnil 
V. chrysanthaHLb, LnilPIPI 
V. chrysanthellaHg, Lg, HLg, MnilnilPmD
V. chrysostachys var. chrysostachysHLbPIPmnilC
V. chrysostachys var. pallidaMb, LMPsPmnilC
V. citrellaMbnilPmnil 
V. comosa     
V. cooloomiaHLb, HPInilPIC, D
V. coronata     
V. crebraHLb, Lnilnilnil 
V. cunninghamii     
V. dasystylis ssp. oestopoiaHLbnilnilnil 
V. decussata     
V. densiflora var. densifloraLBb, Mb, HLb, HnilnilnilD
V. densiflora var. cespitosaHLb, HnilPInil 
V. dichroma var. dichromaLbPIPmnilC
V. dichroma var. syntomaLbnilPmnilC
V. drummondiiHLb ,LnilnilnilD, C
V. endlicheriana var. angustifoliaHLbnilnilnil 
V. endlicheriana var. compactaLb, GnilPInil 
V. eriocephalaLbnilnilnil 
V. etheliana var. ethelianaHLb, LnilnilnilC
V. euradyensis     
V. fastigiataHb, HLnilnilnilD
V. fimbrilepis ssp. fimbrilepisGbnilPInil 
V. forrestii     
V. fragransMb, G, HLnilnilnilD, C
V. galeata    D
V. gracilis     
V. grandifloraLbnilPmnilD, C
V. grandisGb, HLbnilnilnilC
V. habianthaGb, HLnilPInil 
V. halophilaLHb, Mnilnilnil  
V. harveyiLnilPsnil 
V. helichrysanthaHLbPInilPsD, C
V. helmsii     
V. huegelii var. huegeliiHb. HLnilnilnil 
V. huegelii var. decumbensHb, HIbnilnilnil 
V. hughaniiMb, HL, L, LMPmPInil 
V. humilisHLbnilnilnil 
V. inclusa     
V. insignis ssp. insignisGb, HLPIPIPIC
V. insignis ssp. comptaHLbnilPInil 
V. integra     
V. interiorisLbnilPmnil 
V. jamiesonii     
V. laciniata     
V. lehmanniiHLb, LnilPmPsD
V. lepidophylla var. lepidophyllaHLb, G, Lnilnilnil 
V. lindleyi ssp. lindleyiHLb, LnilnilnilD, C
V. lindleyi ssp. purpureaGb, LPInilnil 
V. longistylisHb, HLb, MbnilnilnilD
V. luteolaGb, Lnilnilnil 
V. minutifloraHb, HLnilnilnil 
V. mitchellianaSb, G, HLPmnilPsD
V. mitodes     
V. monadelpha var. monadelphaGb, HL, S, LHnilnilPID
V. monadelpha var. callitrichaLbnilnilnilD
V. muelleriana ssp. muellerianaMb, LnilnilnilC
V. multiflora ssp. multifloraHLb, L, SPIPInilD
V. nitensHLbnilnilPsD
V. nobilisHLb, GnilPInil 
V. oculataLbnilPInilD, C
V. ovalifoliaHLb, LnilPmnilD, C
V. oxylepisHLb, LPInilnilD
V. paludosa     
V. patensLbnilPIPs 
V. penicillarisSb, LnilnilPID
V. pennigeraGb, HL, LPInilnilC
V. pholidophyllaHb, LnilnilnilC
V. pictaLb, GbPInilnilC
V. pityrhops     
V. plumosa var. plumosaLb, HLb, HnilnilnilD, C
V. plumosa var. ananeotesHLbnilnilnil 
V. plumosa var. grandifloraLMb, Gnilnilnil 
V. plumosa var. pleiobotryaGb, HLnilnilnil 
V. plumosa var. vassensisMb, L, GPmPsnil 
V. polytrichaHLbnilnilnil 
V. pritzeliiHLbnilPInilD
V. pulchellaSb, G, LnilnilnilD
V. rennieanaLbPInilnilD, C
V. roei ssp. roeiGb, LMbnilPmPI 
V. roei ssp. meiogonaLbnilPmPI 
V. rutilastra     
V. serotina     
V. serrata var. linearisHLbnilPmnilD
V. serrata var. ciliataHLbPIPmnil 
V.sieberi var.sieberiHLb, GPIPmnil 
V. spicata    D, C
V. staminosa ssp. staminosaLb, GPIPmnilD
V. staminosa ssp. cylindraceaGb, HL, L, M, HPIPInil 
V. stenopetala     
V. subulata     
V. tumida ssp. tumidaGb, HLPIPInil 
V. venustaLbPIPmnilC
V. verticordina     
V. verticillata     
V. vicinellaLbnilnilnil 
V. wonganensis     

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