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Monday, August 5, 2013

Plant of the Month (August) : St. Catherine’s Lace / Giant Buckwheat - Eriogonum giganteum


Giant Buckwheat (Eriogonum giganteum) in Mother Nature's Backyard

Some native plants look good all year long.  Local gardeners depend on them as the seasons change from rainy spring to dry fall.  One such garden stalwart is a large native Buckwheat commonly called St. Catherine’s Lace or Giant Buckwheat.  Eriogonum giganteum is at the peak of bloom now in Mother Nature’s Backyard.

St. Catherine’s Lace is one of several Buckwheats included in our garden.  Southern  California is blessed with a selection of wonderful native Buckwheat species.  They do well in local gardens and are used extensively; they also provide important habitat for insects, birds and other creatures.  For more on local buckwheat species see ‘Plant of the Month’ for July and November, 2012.

Eriogonum giganteum (Giant Buckwheat/
St. Catherine's Lace) provides a spot of fall color

Giant Buckwheat hails from the Channel Islands just off the coast of Southern California.   There are three varieties (natural variants) of Eriogonum giganteum, each endemic to a different island: var. compacta grows on Santa Barbara Island,  var. formosum on San Clemente Island and var. giganteum (the one most used in local gardens) is endemic to Santa Catalina Island.   All variants are uncommon in the wild and species of conservation concern.  Their rarity – as well as their propensity to interbreed with other native Buckwheats like Eriogonum arborescens (Santa Cruz Island Buckwheat), Ashy-leaf Buckwheat (Eriogonum cinereum) and Eriogonum fasciculatum (California Buckwheat) – has prompted the California Native Plant Society to place all three varieties in its Rare and Endangered Plants Inventory.

All forms of Giant Buckwheat grow on dry slopes and rocky cliffs in the chaparral and coastal sage scrub plant communities.   They are hardy plants that survive dry summers, nutrient poor soils and blustery coastal winds.   They also have the flexibility to thrive under water-wise garden conditions, particularly if left to their own devices.



 
St. Catherine’s Lace is one of the showiest local Buckwheats.   Its foliage is gray-green to silvery white;  the foliage is most silvery under dry conditions.   The leaves are much larger than most Buckwheats and provide nice contrast to plants with either green or silver foliage (see photo below).   In most gardens, occasional water keeps St. Catherine’s Lace evergreen.  In the wilds – or with no summer water – the plants are semi-deciduous (lose some leaves).


Flowers of Eriogonum giganteum

Giant Buckwheat produces loads of small Buckwheat flowers (see photo above). The flowering season is late spring to summer: we’ve seen plants start blooming as early as May and as late as August.  The flowers are densely packed in large, rather flat clusters.   The cluster’s texture suggests a heavily embroidered lace, hence the common name ‘St. Catherine’s Lace’.  The young flowers are pink, turning more orange as the season progresses.  The flowers are so numerous – and the clusters so large – that this plant is a show-stopper in many gardens (see photo below). 




Like all Buckwheats,  St. Catherine’s Lace is a great habitat plant.  The many small flowers, with their abundant nectar, attract a wide range of native insect pollinators including native bees, pollinator flies, wasps and butterflies.  A blooming St. Catherine’s Lace will be alive with insects on a warm summer day. Among the butterflies will be the smaller skippers, acmon blues and gray hairstreaks plus a few larger butterflies. In the fall, the red-brown seeds are a treat for migratory seed-eating birds like finches.  What fun to watch on a warm fall day!  Mature plants also shelter birds and lizards all year long.

St. Catherine’s Lace is the largest of our S. California native Buckwheats, attaining a mature garden size of 5-8 ft. tall and wide.  Gardeners should carefully note the size;  this is a large plant that needs sufficient space to grow.   Choose one of the smaller Buckwheat species if space is limited.
 
St. Catherine's Lace after fall pruning


Like most local Buckwheats, St. Catherine’s Lace is a sub-shrub, with woody lower stems and herbaceous new growth.    The overall shape of mature plants is rounded and dramatic, with several main stems.  In fact, this species is best if left to develop its natural form, with only a little shaping.   We prefer to leave the orange-brown flower clusters in place until the birds have eaten most of the seeds.  The spent flowers provide a nice touch of fall color in the autumn garden.  Prune off the dead flowering stalks in late fall for a neater appearance (see above).  Often this is all the pruning that’s required.




Giant Buckwheat is surprisingly tolerant of garden conditions if not coddled too much. It does well near the coast as well as in hot inland gardens.  While its native soils are rocky and well-drained, it thrives even in clay (with judicious summer water) and requires no fertilizer.  It does well in full sun or part shade.  In fact it is quite easy and adaptable, even growing under eucalyptus trees with their thick natural mulch (see above).    Plants require only occasional summer water to look attractive.  Let the soils dry out between waterings, then water deeply.  In clay soils we usually water once a month or less in summer, depending on temperature and wind.

Eriogogum giganteum paired with 'Winifred Gilman' Salvia

St. Catherine’s Lace looks beautiful paired with Salvias (see above), other Buckwheats, white-foliage plants like Catalina Silverlace (Constancea (Eriophyllum) nevinii) and evergreen shrubs like Coyote Bush (Baccharis pilularis) and Ceanothus. It does well on slopes and can even be grown in large containers.  Some gardeners use it for an informal hedge.  Its dried flower clusters make a dramatic addition to floral arrangements. And Native Californians used St. Catherine’s Lace for medicines to relieve headaches and stomach aches.

As a final note, we return to the observation that native Buckwheats are notorious in their ability to hybridize.  The propensity of Buckwheats to hybridize (produce crosses between two species) is both good and bad.   Hybridization can be advantageous to wild populations during times of environmental change. In fact, it’s one way that some new species are eventually formed.   For the nursery propagator and gardener, hybrids can be  a source of plants with new, desirable traits.   So easy hybridization does have its positive side.

On the other hand, the propensity of Buckwheats to hybridize has plant ecologists worried.  As native gardening increases, plants once separated geographically are now coming in contact.   Hybrid Buckwheats are beginning to pop up in home gardens.   More alarmingly, hybrids are also occurring among wild populations of Buckwheats!  These hybrids are a direct consequence of plants in gardens and highway plantings:  bees transport pollen from garden to wild land -  and hybrid  plants are the result.

While hybridization may seem innocuous, the potential consequences are serious. The very characteristics that differentiate one species from another are in danger of becoming lost.  Each species has intrinsic value - in addition to its potential as medicine, food or other material.  The loss of a species is not something to take lightly; once lost, a species may be lost for good.   

Some scientists argue that buckwheat species should only be planted within their precise local range. That’s probably a good idea, although a bit late in coming in the case of Buckwheats.   At the very least, we should consider the impact of our gardening choices.  If you live near (say within ½ mile) of a population of wild/natural Buckwheats, consider planting only plants derived from the local population.   That’s a responsible choice; one that will help conserve the local native genes.  If you live in an urban area, your choices are more open, but you still might want to choose a local native species over one from further afield.  
 
 
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