Plant of the Month (July) – Narrowleaf Milkweed (Asclepias fascicularis)

Monarch Butterfly on Narrowleaf Milkweed (Asclepias fascicularis)

Many gardeners appreciate the special relationship between Monarch Butterflies and Milkweeds.  Far fewer know the Milkweed species that are actually native to Los Angeles County.  We’ve chosen the native Narrowleaf Milkweed as our Plant of the Month in honor of our annual Butterfly Month (July).

With increasing interest in Monarchs, Southern California gardeners have flocked to the brightly colored ‘Mexican Butterfly Milkweed’, Asclepias curassavica, a yellow-orange-red flowered species from Central America.  This Milkweed does indeed provide food for Monarchs.  But it’s not native and it spreads like the dickens!   Better to plant a local Milkweed to attract this favorite garden visitor.

Local native Milkweeds add a touch of sophistication – and good butterfly habitat – to many local gardens. One of the more widely used is the Narrowleaf Milkweed, Asclepias fascicularis.  This pretty, drought-tolerant native is blooming right now in Mother Nature’s Backyard.

Milkweeds are grouped in the genus Asclepias, whose name honors the Greek god of healing.  Many Milkweeds are used traditionally as topical medicines for sores and skin infections, even though they are considered poisonous plants (see below for more).   Our local native species include the Narrowleaf Milkweed, Indian Milkweed (Asclepias eriocarpa) and Showy Milkweed (Asclepias speciosa).  We currently have all three planted in Mother Nature’s Backyard.

Narrowleaf Milkweed grows in summer-dry places below about 7000 ft. elevation in the western United States from Washington and Idaho south to Baja California, Mexico.  Voucher specimens exist for the Dominguez Slough (now the Gardena Willows Wetland Preserve and the location of Mother Nature’s Backyard) and other local areas.   It grows in many California plant communities, mostly away from the immediate coast.   Common to all are soils that are well-watered in winter-spring and dry with summer.

Clump of Narrowleaf Milkweed

Narrowleaf Milkweed is an herbaceous perennial that dies back to the root each fall-winter.  Plants have a deep, sturdy taproot that allows them to grow and flower during the warmer months.   In our area, new foliage typically doesn’t appear until the weather begins to warm up in late April or May. 

 

Asclepias fascicularis - note narrow, folded
 leaves arranged in whorls

The leaves of Narrowleaf Milkweed are long (up to 5 inches) and narrow, making this species more delicate appearing than other Milkweeds. The leaves are usually folded slightly along the midrib (the major vein in the center of the leaf) and arranged in whorls (spiral-shaped groupings) along the upright stems.  The stems themselves are one to three feet tall and slender; a single plant will produce more stems each season.   The overall impression of this plant is of a delicate, open tracery that complements many other types of garden foliage (see picture, above).

The flowers of Narrowleaf Milkweed are a pale, creamy pink – a boon to gardeners who love pinks and reds.   Like most Milkweeds, the flowers are grouped in ball-like clusters, which may contain more than 50 flowers.  The individual flowers are small (1/4 inch; 1 cm.) and have a shape typical for Asclepias. Their unusual shape is due to fusion and modification of the usual flower parts.  The five waxy pink petals (seen at the base of the flowers, below) are reflexed down when the flower is fully open. 

Cluster of flowers - Asclepias fascicularis

The corona (crown-shaped structure above the petals) is composed of five ‘hoods’ and ‘horns’ which are modifications of the male sex organs.  In the very center is a complex structure (the gynostegium) composed of fused parts of both male and female organs.  The hoods and horns are appropriately named; as seen above, they indeed look like hoods and horns.  They point towards the anthers (the pollen producing structures), which are fused to the female stigma (the pollen-receiving structure) to form the gynostegium.  For excellent labeled drawings of these structures see: http://waynesword.palomar.edu/termfl1.htm

 

The pollen is stored as pollen masses (pollinium) rather than separate pollen grains.  When a pollinator insect visits the flower, its legs slip into the slits between anthers on the gynostegium.  If you look closely, you can see these slits in the picture above; there are 5, radiating out from the very center of the flower.   When the leg is removed, it takes with it a pollinium, which is deposited into the stigmatic slit of the next flower.  From then on, it’s fertilization as usual.   For more on pollination see our ‘Planning for Pollinators’ post (June 2013).

Given the unusual flower structure, you might expect pollination to occur only rarely.  Quite the contrary: the highly modified structures, and the lure of sweet nectar, insure that Milkweed pollination is highly efficient.   Numerous seeds develop within the narrow, sharply-pointed seed pods.  At maturity, the pods split open, releasing the brown seeds with their fluffy ‘parachutes’.  Wind deposits the seeds around the garden; so you may find new patches growing in favorable locations.

 

Narrowleaf Milkweed with Large Milkweed Bug
 (black and orange) and yellow Oleander Aphids

Narrowleaf Milkweed is an excellent insect habitat plant.   Its nectar provides food for butterflies, bees and wasps.  In our area, the seed pods are eaten by the Large/Common Milkweed Bug (Oncopeltus fasciatus).  The foliage is eaten by a range of interesting insects including true bugs, beetles and larva of the Monarch and Striated Queen butterflies.  The yellow ‘Milkweed Aphids’ (Oleander Aphids; Aphis nerii) that suck the sap of Milkweeds are not native; they can also decimate a Milkweed plant.  The best advice is to blast them off the plants with a stream of water when you first see them.  For more discussion on dealing with these aphid pests see: http://articles.latimes.com/2012/nov/09/news/la-lh-milkweed-aphids-monarch-butterfly-eggs-20121104

Monarch and Queen caterpillars are hardy eaters, especially during their later stages.  Milkweed plants can look a little ‘eaten’ by the end of the summer, but that’s a normal consequence of a healthy ecosystem.  The caterpillars, which are well camouflaged, are also protected by chemicals produced by Milkweed plants.  These chemicals, the cardiac glycosides, protect the plant from being eaten; they are toxic to many insects and larger animals, including humans. The caterpillars, which are immune to their effects, use these chemicals to deter their predators.

Native Californians used the Narrowleaf Milkweed in several ways.  Parts of the plant were used to prepare topical (external use) medicines.  Some plant parts – carefully and properly prepared – were even eaten.  But caution is advised with any Milkweed; they do produce toxic chemicals.  To be safe, no part of the Milkweed plant should be eaten or made into tea or medicine.   Gardeners with pets or children with a propensity for eating garden plants should take this into account when considering Milkweeds.

Narrowleaf Milkweed was also an important source of fibers for Native Californians. The dried stems were split and rolled on the thigh to release the tough fibers.  These were then used to make string for nets, rope and other cordage uses (decoration on clothing, etc.).  It takes a lot of Milkweed to make a net (hundreds to thousands of stalks)!

Narrowleaf Milkweed is quite easy to grow.  It does well in full sun to part-shade in most local soils, from sandy to clay.  The plants like plenty of winter/spring moisture and can even tolerate winter flooding.  But once established, they are remarkably drought tolerant.   In our garden we treat them as Water Zone 2 plants, watering them occasionally in summer (see ‘Water Zone Gardening’ – posted April 2012).   Overwatering Milkweeds can cause them to become invasive.

As for many local native plants, we taper off watering in the fall (late August to October). This allows the plants to enter dormancy.   Milkweeds should be cut down to 1-2 inches in fall.  They will re-spout strong and healthy in spring.  And that’s about all there is to growing Narrowleaf Milkweed.

 

Narrowleaf Milkweed in Mother Nature's Backyard

Milkweeds make a delightful addition to the home garden.  Their foliage and pastel flowers provide a delicate old-fashioned note to the flower garden.  They are a must for anyone wanting to provide Monarch and Striated Queen habitat.  So consider adding some native Milkweeds to your garden.

For a gardening information sheet and more pictures of this plant see: http://nativeplantscsudh.blogspot.com/p/gallery-of-native-plants.html

 

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please feel free to add your comments below.  We welcome your Milkweed questions at: mothernaturesbackyard10@gmail.com