Garden Notes: Sour milkweed threatens butterflies

Garden Notes: Sour milkweed threatens butterflies

The lively and mellow Living Local/Harvest Fest took precedence over my being able to participate in the “Goldenrod: Identification of Island Species” workshop, interesting as it was to me, which was offered by Melissa Dow Cullina at Polly Hill Arboretum last Friday and Saturday. On my own, however, I am thrilled to find in my neighborhood plants of Solidago caesia (bridal-wreath goldenrod), listed in “The Flora of Martha’s Vineyard” as rare on Martha’s Vineyard, though once common.

I had never seen the plant, with slender, interrupted wands of golden yellow composite flowers, on the Island or in person, until I became acquainted with it at the Garden in the Woods, Framingham, and the Mt. Cuba Center in Delaware. At least, not consciously, though there are times, when being led by the nose up to something novel, one sees it more easily after the “formal introduction.”

Then, maybe four years ago, on a walk to the mailbox, I spotted a solitary S. caesia plant. I had to pinch myself to believe what I was seeing. Last year there were perhaps four plants, all nearby to each other, and now, 2010, more are in more places, and separated by perhaps 100 yards.

Monarchs, Milkweeds, and Black Swallowwort

For many people, older as well as younger, the way into a greater overall interest in nature lies through a singular or vivid experience. It might be a youthful fishing derby, or being in a kindergarten class with an observation beehive or ant farm, or a close encounter with a spectacular wildflower.

For many Islanders, our environs being well supplied with milkweed species (according to the above-cited text: Asclepias exaltata; A. incarnata, A. purpurascens; A. syriaca; and A. tuberosa), a sense of connection or awareness of monarch butterflies may start with a yellow and black caterpillar, a green and gold-flecked chrysalis, and a peanut butter jar containing milkweed leaves.

From then on one’s interest grows. It is a benign progress: butterfly gardens follow where plants to support caterpillars or adults are grown; butterfly counts, similar to Christmas bird counts, become entertainment; additional butterfly species become recognizable and interesting.

Now, however, an alarming invasive grows in several areas of the Vineyard. It could easily degrade the prime monarch habitat and display we enjoy here. A European member of the milkweed family, black swallowwort, (Vincetoxicum nigrum) has the right odor for monarch females, and possibly other species, sniffing out milkweeds as proper places to lay their eggs. The eggs laid on black swallowwort, however, fail to develop and never hatch. It is estimated that given the choice between common milkweed and black swallowwort, 25 percent of female monarchs will oviposit on the black swallowwort, leading to a plausible loss of one quarter of Island monarchs!

Efforts to keep Vincetoxicum nigrum in check are uneven at best, due perhaps in part to the plant’s resemblance to vinca. As the photos show, the plant is elegant looking, as if “it might be something,” i.e., an unknown perennial. It forms fleshy root rhizomes deep in the ground that persist and continue to send up growth after shallow weeding. The vining plants look quite beguiling festooned with their slim pods, which when ripe release their seeds in classic milkweed fluff, drifting away to form new colonies. This is the “formal introduction.” Please learn to recognize black swallowwort and help eradicate it.

In the garden

Houseplants outdoors: be alert for sudden frosts. Lulled into an endless-summer mentality by the weather, I recently had an “uh-oh” moment. Belatedly it was time to lug my amaryllises (hippeastrums really) and Thanksgiving and Christmas cacti down into the dark of the cellar; normally, around Labor Day is the right time. This fixes the budding process properly in their plant-brains so that they flower when we want them to, not following their own inclinations.

Cutting back and cleaning up where possible continues to be the focus of work in the ornamental garden, making it far easier to fertilize and lay mulch. Many Island roses come back to life, Lazarus-like, in the Vineyard autumn. Continue to prune and deadhead, but hold off on the fertilizer. Late autumn, when it is really chilly and growth has stopped is, in my opinion, a better time to mulch or manure than now. Otherwise, there is always the danger of pushing the plant into new growth when it is preferable to be hardening off.

There is a window for shrub planting and lawn repair during the Vineyard autumn, and sale prices are good at Island garden centers. So is the variety. I would focus on bushes, shrubs, and small deciduous trees, bulbs too, for fall planting; personally, my preference is to plant conifers and hollies in early spring.

The classic Island winter features many cycles of freeze/thaw, sunshine/overcast — although our weather patterns do seem to be in a state of flux. This makes a harder adjustment for conifers when newly planted because they are functioning all winter. The deciduous trees are dormant, seemingly safely in dreamland throughout winter, although they too may be stressed by abrupt temperature changes.

Lay a mulch of compost or well-rotted wood chips. Water the new plants daily for the first week, weekly for the first month; winter rains [should] take over sometime in November. Are there plans for a living Christmas tree this year? Decide the location now and prepare the planting hole – wider for good root spread, rather than deeper.

An addendum to several recipes I gave in recent columns: Tomates confutes and Quince Cheese, or any recipes made using low oven temperatures of 225°F, could be made energy-efficient by using a “dead” or unused car parked in the sun as the oven!