California Milkweed

Year-round

California milkweed is a sun-loving, drought-ready monarch plant that goes semi-dormant in summer.

• Calscape lists full sun, very low to low water needs, and summer watering of at most twice a month once established.
• It tolerates sand and clay, grows about 3 feet tall and wide, and tolerates cold to 5 degrees F.
• Calscape says it hosts 8 native butterfly and moth species and recommends planting only locally native milkweed for monarchs.
• ASPCA lists milkweed (Asclepias) as toxic to dogs, cats and horses, so keep pets from chewing it.

Fall

Fall needs almost nothing from you.

• Keep watering minimal because it is a low-water plant.
• Spent growth can die back as part of its summer semi-deciduous habit.
• Keep pets away from any fallen stems or leaves, per the ASPCA listing.

Winter

Winter cold is no problem for this plant.

• It tolerates cold down to 5 degrees F.
• Fast, medium or slow drainage is all listed, but soil that stays soggy is not described as suitable.
• Skip extra watering while it rests.

Spring

Spring is bloom time and a good moment to plant.

• It flowers in spring and summer in lavender, pink or white.
• Bees, butterflies, moths and hoverflies visit.
• Water young plants regularly while they establish, then ease off.

Summer

Summer is dry season, so water very little once established.

• Water no more than 2 times a month once established.
• Calscape lists it as summer semi-deciduous, so leaf loss is expected.
• Monarchs are confirmed visitors, so avoid pesticides near it.

Year-round

California milkweed grows natively in California, including the Transverse and Peninsular Ranges, the same mountain systems that frame the Los Angeles basin, plus the central Coast Ranges and southern Sierra Nevada foothills, in coastal sage scrub and chaparral. It is an early riser, breaking dormancy in March or April ahead of most other native milkweeds, which makes it valuable to monarch butterflies returning from coastal overwintering sites. It is a required host plant for monarch caterpillars, and the genus Asclepias is listed by the ASPCA as toxic to dogs, cats, and horses, so keep it out of spots where pets graze.

• Plant in full sun with fast to medium draining soil. It tolerates both sandy and clay ground once established.
• Once established, water no more than about twice a month during the dry season. More than that raises the risk of root rot in this drought-adapted plant.
• Expect the woolly gray-green foliage and lavender to pink flower clusters to die back later in the year. That is the plant following its natural growth and dormancy cycle, not a sign of trouble.
• Keep it out of areas where dogs or cats regularly graze on foliage. The milky sap contains cardiac glycosides.

Fall

By fall, California milkweed is typically dormant. The foliage has died back to the root crown while it waits out the dry season before the Mediterranean climate's winter rains return.

• Resist the urge to pull it out when it looks dead. The roots are alive underground and will resprout once the rains start.
• Mark the spot with a small stake or label so the dormant crown does not get weeded out or disturbed by mistake.
• Fall is a reasonable time to direct-sow seed if you want more plants, since seed gets the same rain cues the species is adapted to.
• Skip supplemental water on the dormant crown. Extra moisture during dormancy raises the risk of rot.

A small stake or label over the dormant crown keeps a bare-looking patch from reading as an abandoned or dead bed during a front-yard walk-through.

Winter

Winter is the wet season in the Los Angeles area's Mediterranean climate, and California milkweed's root system uses that rain to prepare for its early spring emergence, usually ahead of most other native milkweeds.

• The crown stays dormant through winter, so there is usually no top growth to care for yet.
• Winter rains typically supply what the dormant roots need. Supplemental water usually is not necessary in a normal rain year.
• This is a reasonable window to plant bare-root stock or container plants, since the coming rains help new roots establish before summer heat arrives.
• Watch for the first gray-green shoots as early as late winter. That is this species living up to its reputation as an early riser.

Spring

Spring is when California milkweed wakes up, often in March or April, well ahead of other native milkweed species. This is its main bloom window and the time monarchs returning from coastal overwintering sites need it most.

• This is the best time to plant new milkweed, while the Mediterranean climate's rains are still topping off the soil.
• Water new plantings deeply once or twice a week until roots establish, then taper off toward the twice-a-month schedule established plants prefer.
• Flower clusters open in shades of lavender to pink and draw a steady stream of native bees along with monarchs.
• Watch for aphids and milkweed bugs on new growth. A strong spray of water or hand removal usually keeps them in check.

Summer

Summer in the Los Angeles area is hot and dry, close to the conditions this plant evolved for. Established California milkweed needs very little supplemental water, and by late summer it starts winding down toward its dormant season.

• Established plants need water at most twice a month. More than that risks root rot in this drought-adapted species.
• Bloom can continue into early summer before flowering tapers off for the year.
• As days shorten, do not be surprised to see leaves yellow and drop. That is the start of its normal summer into fall dormancy.
• Caterpillars may strip leaves down to bare stems. That is the plant doing its job as a monarch host plant, not damage that needs fixing.