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An Autumnal Cadenza Wraps up the Season

November 20, 2022

November weather this month was unbelievable, with highs of 78, followed by daring chills of 38 degrees. A classic performance, winter’s arrival and autumn’s completion are reliable, but the handoff is...less reliable. I like to think of this seasonal transition as a cadenza, a flourish of improvisation that wraps up a musical composition. Cadenzas include callbacks to the melody, phrases plucked from the original composition but instilled with fervor or ornate nuances. Like an Abelia grandiflora that bloomed in summer, but is back right before frost with more flowers.

Gardeners know that frost will arrive and that there are many tasks they need to make happen before that event. As to when it arrives, however, we can only make well-educated estimates. Here is our own “autumnal cadenza.”

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Wave Hill Gardener Kevin Hennessy preps cuttings for winter. He’ll remove the bottom leaves from vegetative cuttings, dip one to two nodes into rooting hormone and plug them into a compact soil mixture of perlite and other materials.

Many “annual” plants, plants that cannot survive the frost and are typically enjoyed for summer and autumn, are in fact perennials in their native range. Some favorites include salvia and coleus, which grow in many areas at Wave Hill. Gardeners have been taking herbaceous cuttings of these plants for the past few weeks, but time is running out—these cuttings must be harvested before frost.

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Trays of tender perennials sit at the mist bench at the west end of the Tropical House.

Taking vegetative cuttings is an easy task, but keeping them happy through the winter can be difficult without the correct conditions. Cuttings should be happy in the Tropical House, which is kept warm and humid.

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Tropical plants from the Monocot Garden and other areas are dug up and moved inside for the winter.

Plants not hardy to the New York City winters will be moved indoors for storage. Some of these plants respond well to simply getting dug and potted up. Those with underground storage organs (bulb, corm or rhizome) prefer to be dug and cleaned before storing. Among the familiar plants that prefer the latter are caladiums, cannas and dahlias.

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Wave Hill Gardener Gelene Scarborough rinses dahlia tubers, which will dry before they are placed into a storage vessel filled with vermiculite, a coarse natural mineral that absorbs water and aids with aeration.
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Seed-saving in the Alpine House. Wave Hill Gardeners sometimes share seeds with organizations like the Hardy Plant Society and North American Rock Gardening Society. Check out those organizations for seed swaps!

Seed-saving is another way to keep plants in the garden. Fruits, which contain seeds, are best collected before cutback occurs because they are delicate and could easily break. Seed-cleaning can happen whenever there is downtime, making it a perfect task for a chilly December day. Clean and viable seeds should be stored in a dry, cool environment for best germination rates.

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Cutback in the Wild Garden accentuates natural shapes in the garden beds. Many perennials will remain through the winter to offer interest, food and shelter for wildlife. Those that were removed were repurposed in a temporary structure for hungry chickadees by Wave Hill Gardener Sandra Schaller.
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Gardener Kevin Hennessy uses an electric-powered mower to chop fallen leaves. Chopping the leaves increases surface area, allowing for speedier decomposition.

A closed-loop system has been in place for many years for reusing leaves at Wave Hill. In autumn, many leaves are left where they fall, offering insulation and habitat in garden beds and tree pits. Those that fall on pathways are collected and composted into leaf mold, which is spread in garden beds during the growing season. Finally, leaves that fall on the lawns are chopped and left in place. All these applications allow leaves, which are high in phosphorus and carbon, to reenter the ecosystem and gradually feed the topsoil with nutrients.

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Wave Hill Gardener Christopher Bivens (right) and volunteer Kevin Childress make the final cutback in the Aquatic Garden, before submerging plants that can survive the frigid water.

The Aquatic Garden is an area that expresses dormancy as early as August. Tropical water lilies cannot stand cooling water temperatures, so their leaves die off early, revealing red and yellow pigments. Pots of hardy native plants like Typha latifolia (cattail), Pontederia cordata (pickerelweed) and Nymphaea odorata cvs. (hardy waterlilies) are lowered to the bottom of the pool for the winter. The whole pool is about 22 inches deep but the northwest corner, where the drain is located, is the deepest, with about 27 inches of water. This corner will act as a nursery for overwintering Cyperus spp. which made up a Nile River-themed summer display. Tender plants like Cyperus spp. are usually stored indoors or in deep pools. There is no space inside for these large plants, so Bivens is experimenting with this outdoor storage option.

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During the final days of the John Nally Interns’ eight-month apprenticeship at Wave Hill, they were able to participate in bulb-planting across the garden. Intern Janine Rosario plants Narcissus ‘Stainless’ in a mixed-bulb planting at the Kate French Terrace.

Bulb-planting can be delayed as long as the ground isn’t frozen. Wave Hill’s 2023 bulb displays will look different from previous years due to industry bulb-shortages and an extremely wet spring in 2022. The latter encouraged a significant tulip botrytis infection across many seasonal beds, such as the Paisley Bed, the Kate French Terrace and Pergola. Resistant plants, such as daffodils, grape hyacinth and camassia, will be planted in an effort to reduce future infections.

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There are many bulb-like plants going in the ground during late-autumn, Eremurus spp. (foxtail lilies) is one genus that produces a tuberous root and must be planted quickly otherwise it will dry out.

There is still much to be done to complete this “autumnal cadenza”. Many bulbs must get in the ground, tender plants are still getting moved indoors and the gardens must be tidied and tucked away for winter slumber. Not everything is slowing down. Doors for the Conservatory and roof panels for the Alpine House go on, helping keep warm air in and cold air out, awakening these plants from warmer regions of the world.

Jess Brey,
Ruth Rea Howell Senior Horticultural Interpreter