Milkweed Pruning Guide: Do I Deadhead Milkweed Plants
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By: Bonnie L. Grant, Certified Urban Agriculturist
We know milkweed is a crucial plant for Monarch butterflies.Growing the plants will attract and feed these beautiful butterflies. But youmay be asking, “should I prune milkweed.” Milkweed pruning isn’t really necessary,but deadheading milkweed can enhance appearance and encourage furtherflowering.
Do I Deadhead Milkweed?
Milkweedis a glorious perennial wildflower native to North America. All through summerand into fall the plant is covered with flowers. It is a perfect plant in thenative garden or just to colonize a vacant field. The blooms are excellent cutflowers, and in the garden, they are attractive to beesand butterflies.
Deadheading milkweed is not necessary but it will keep theplants looking tidy and may promote further blooms. If you do it right afterthe first flowering, you can expect a second crop of blooms. Cut the blooms offjust above a flush of leaves when milkweed deadheading. This will allow theplant to branch and produce more flowers. Deadheadingcan also prevent self-seeding if you don’t want the plants to spread.
If you are growing milkweed in zones outside of USDA 4 to 9,you will want to leave the seed heads to mature and reseed the area or,alternatively, cut them off when brown and dry and save the seed to sow inspring.
Should I Prune Milkweed?
In cases where the plant performs as an annual, cut back thestems to the ground in fall and scatter seeds. New plants will grow in spring.Perennial plants will benefit from being cut back in late winter to earlyspring. Wait until you see new basal growth and cut the old stems back to about6 inches (15 cm.) from the ground.
Another method of milkweed pruning is to cut the plant back athird of its height. Make cuts just above a leaf bud to prevent unsightly barestems. This is a really hardy plant in most regions and can withstand rathersevere pruning to rejuvenate it or simply get the plant ready for new springfoliage and stems.
Tips on Milkweed Pruning
Some gardeners may find the sap of the plant irritating. Infact, the name refers to the milky latex sap, which can cause skin irritation.Use gloves and eye protection. Use clean pruning tools that have been wipedwith alcohol or a bleach solution.
If pruning stems for cut flowers, sear the end with a litmatch to seal the cut and prevent the sap from leaking out. If you wait toprune flowers, you can expect ornamental fruit which are also attractive indried flower arrangements.
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The Monarch is unquestionably the most recognized and beloved butterfly in North America. It belongs to the subfamily of tropical milkweed butterflies, which are named after their host plant, the milkweeds (Asclepias species). Scientists believe that, originally, the Monarch followed milkweeds as they spread northward after the Ice Age. Unlike the plant, however, the butterfly can't survive cold winters and must return south to wait out the cold months.
Milkweeds for the Garden
Plant any of the following milkweeds in your garden and you'll be helping the beleaguered Monarch butterfly.
- Asclepias asperula (antelope-horn milkweed): Southwest native. Grows to 2 feet with narrow leaves and pale green flowers. Prefers dry soil.
- A. curassavica (bloodflower): Tender perennial from Mexico. Grows to 3 feet with yellow-centered red flowers. 'Silky Gold' has yellow flowers.
- A. fascicularis (narrowleaf milkweed): West Coast native. Grows to 3 feet with pale pink flowers. Prefers dry soil.
- A. incarnata (swamp milkweed): Eastern native. Grows to 4 feet with pink flowers. 'Ice Ballet' has white flowers. Prefers moist soil.
- A. speciosa (showy milkweed): Western native. Grows to 4 feet with light pink flowers. Tolerates dry soil.
- A. sullivantii (prairie milkweed): Rare Midwestern native. Grows to 2 feet with reddish purple flowers. Prefers moist soils.
- A. syriaca (common milkweed): Eastern native. Grows to 5 feet with fragrant lavender flowers. Spreads rapidly by rhizomes.
- A. tuberosa (butterfly milkweed): Eastern and Southwestern native. Grows to 3 feet with showy orange, red, or yellow flowers. Prefers dry soil.
- A. verticillata (whorled milkweed): Eastern native. Grows to 2 feet with narrow, threadlike leaves in whorls and white flowers.
Over a hundred species of milkweed are native to North America, and many are spectacular candidates for any garden (see "Milkweeds for the Garden"). They range from the tropical bloodflower (Asclepias curassavica), to the moisture-loving swamp milkweed (A. incarnata), to the now-scarce prairie milkweed (A. sullivantii). Milkweeds certainly are a must for every butterfly garden. Their leaves provide a home for Monarch eggs and a feast for Monarch caterpillars. Even better, hordes of adult Monarchs are drawn to their starburst flower clusters to sip nectar.
In nurseries, you're most likely to come across butterfly weed (A. tuberosa). It's showy, adaptable to poor soil, and well behaved. It won't take over your flowerbed like common milkweed (A. syriaca), which spreads aggressively by underground rhizomes. Butterfly weed's blossoms range from orange to red to yellow 'Gay Butterflies' is a seed mix including all three colors.
Common milkweed may be a rambunctious grower, but many butterfly gardeners wouldn't be without it since it's the plant of choice for millions of Monarch caterpillars. The stout stem of the common milkweed grows up to six feet tall and is covered with fine hairs and wide, smooth leaves. In summer, it bears many large, fragrant, but somewhat dull purplish-pink flowerheads.
Until recently, the best way to get common milkweed seeds for your garden was to collect them from plants growing on the roadside. Nowadays, they are available from several nurseries (see Nursery Sources). Since seed-started plants can take up to three years to flower, however, you might want to ask a friend for a plant or get permission to remove milkweed from an area slated for development.
"The best way to propagate common milkweed is to find a main rhizome coming from the plant and work it out of the soil," says Minnesota Master Gardener Cathy Leece. "Aim for a one-foot piece with roots and above-ground growth."
Replant the rhizome at the same depth in sun or part shade keep it watered and mulched and trim back wilted growth. New sprouts should appear by late summer, growing into one or two plants the following year. Because of its tendency to spread, it's a good idea to keep common milkweed out of formal flowerbeds and in more natural areas of the garden. Should it become unruly, dig up rhizomes as they sprout new growth. Be persistent because they may be a foot or so underground.
For a more cultivated alternative to common milkweed that's almost as attractive to egg-laying Monarchs, Leece suggests swamp milkweed. Like most other milkweeds, it has fibrous roots and therefore won't take over your flowerbed. It's an enthusiastic self-seeder, so remove seedlings or share them with friends. These seedlings may bloom the following year, with attractive, long-lasting, pink flowerheads that have less of a "wild" look about them than those of the common milkweed. Be sure to plant swamp milkweed in a moist site.
All milkweed seeds, with the exception of the tropical bloodflower, should be stratified before planting: put them in a ventilated plastic bag or container of moistened sand or moss, and refrigerate for about four weeks. Milkweeds can also be propagated successfully from stem cuttings.
Common milkweed leaves and roots are toxic to humans, but only if it is consumed in large amounts. The plant has actually been a food source for Indigenous tribes, who carefully prepared it by cooking. Wild-food enthusiasts continue to cook and eat the plant today. However, eating large quantities of unprepared milkweed may cause bloating, fever, difficulty breathing, dilated pupils and muscle spasms, and the result can, in very rare instances, be fatal.
Because the leaves are bitter, it is unusual for people or pets to deliberately eat milkweed, but grazing animals are sometimes poisoned by them. These plants are generally not a serious hazard in the home garden, but children should be kept away or warned.
Blundering Gardener: when – and when not – to deadhead
Is it too late to deadhead perennials?
That is the question I ask myself as I gaze out the window at the milkweed and yarrow that are going to seed. Usually, if I understand what each plant is trying to accomplish, I can figure out what to do with it.
So why do plants bloom in the first place? To procreate. Plants are obsessed with their species’ survival and could not care less about their own individual well-being. And beauty is beside the point. The prettiest rose has no advantage over a plain one.
We humans do wield a lot influence. We skew the odds in favor of what we value — hardiness, disease-resistance, beauty — by arranging marriages between plants that have those desirable traits. The plants are still in charge, though.
Annuals, called monocarpic because they flower only once, have only one shot at species survival. Naturally, they are going to give it their all. They flower like mad. Deadheading lengthens the bloom period by eliminating seed production. Stymied in its effort to jump-start a second generation, the plant has to start all over again with fresh buds.
At the opposite extreme are the elders: Some long-lived monocarpic plants need decades to gather the strength to create a single, usually stupendous and often stupendously stinky, flower.
Corpse flower, for example, smells like rotting flesh, hence its name. Carnivorous insects attracted by the stench do their bit for procreation by picking up its pollen and passing it on.
Some plants live two years. Foxglove, for example, is a much-loved biennial.
Perennials live longer but, like the biennials, usually don’t bloom until age 2. Some have long periods of bloom that can be lengthened through deadheading. Others bloom profusely in a single flush. There are rebloomers, too, though their second act will benefit from a push from the pruning shears.
Dundee Nursery offers an excellent “fact sheet” online (dundeenurseries.com) ex-plaining how and when to deadhead perennials, which ones are invasive, which have pretty seedheads and much more.
The fact sheet offers tips on what you can do to help the pollinators. Bees and butterflies are attracted not to the seeds of plants but to their flowers. These have sweet and often fragrant nectar inside. When the pollinator picks up pollen (i.e., plant sperm) along with its meal, the pollen hitches a ride to the next flower in its family the pollinator feeds on and fertilizes it.
I was wondering if I should deadhead my swamp milkweed or let the flowers go to seed. Which would be better for the monarchs? The Dundee fact sheet recommends keeping the flowers coming as long as I can but letting the large seedheads open and spread around to increase the size of my patch for next year’s butterflies.
There’s no point in deadheading late-blooming Russian sage or plants with massive flowers, such as peonies. It’s just too much to ask a plant to do all that work all over again in one year.
Hostas? Forget about it. I’m not a fan of hosta flowers anyway, except the ones that perfume my garden, such as H. plantiginea “Aphrodite.”
Actaea, astilbe, filipendula and goatsbeard are not rebloomers. There are many others.
Shrub roses flower abundantly and for a long time. In this way, they’re more like perennials than woody plants, which typically flower all at once and then stop for the season.
I still have an early Explorer series rose called William Baffin that covers itself in pink flowers in June before petering out. Selective deadheading keeps it going, a flower here, another there.
A tender tea rose is my busiest bloomer, putting out flower buds from May well into October. But almost as prolific are the new varieties of ever-blooming hardy shrub roses in the Carpet Rose series, as well as Bailey Nurseries Easy Elegance roses, Knockout, Modern’s Blush, the Carefree roses and a stunner called Morning Magic.
What’s remarkable is that these new roses grow on their own roots. Most hardy roses used to be grafted onto a hardier rootstock, usually a wild rose native to extremely cold regions.
Occasionally one of my older roses will revert to the thorny, small-flowered tough guy lurking below the surface. Sound familiar? My advice is to remove the upstart canes as they poke up from down under. This will slow the takeover. But eventually the outlier will win. It’s just responding to the call of nature, after all.
So unless you have a weakness for underdogs, you’ll probably want to dig up the entire plant and toss it out.
THIS WEEK’S TO-DO LIST
— Sow some cool-weather crops, such as lettuce. The weatherman keeps saying he can smell winter coming.
— Don’t be so wowed by your gorgeous kale or chard that you forget to harvest it. All leafy vegetables taste best when they’re tender, i.e. young. The leaves will grow back.
— Wondering where all the juneberries went? Aka serviceberries, these luscious little fruits are ripe and delicious … or they would be if you had protected them from hungry birds. Next spring, put a tree net over the canopy. This works for other fruit trees, too. Throw the net over the shrub at bloom time.