By Barry Davidson
Edited by James Pethybridge
Former National President of the Australian Rhododendron Society, former Editor of ‘The Rhododendron’, and established grower in Claremont, Tasmania.
Frequently, newer members of the horticultural community ask about deadheading: What is it, why do we do it, and how do we do it? As established growers, we do ourselves a great disservice if we appear divided on the merits of this very basic horticultural procedure. The lack of consensus and understanding among recognized growers is quite surprising, as was recently revealed in an online email group.
In Australia, we expect each presently flowering shoot to produce two or more flowering shoots the following year—provided the plant is in a well-lit position with adequate fertilizer, water, good drainage, and is deadheaded promptly after flowering. Not only is future flowering promoted by deadheading, but most would agree that the appearance is far more aesthetic. This article presents the definitive evidence for the practice.
What is Deadheading and How Do We Do It?
Deadheading is the removal of dead flowers and young seed pods. It is best done immediately after the flowers are past their peak. Methods vary depending on the variety:
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Elepidotes (Large-leafed varieties): Take the truss between the index finger and thumb and bend it sharply. This easily deadheads most elepidotes. If the spike is curved, bend the stalk outwards to snap it cleanly.
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Lepidotes and Vireyas (Small-leafed varieties): These varieties require more care. The standard snapping method will often take the top few leaves with it. For these plants, a careful stripping and nipping action is necessary.
Historical Wisdom: The Energy Drain of Seed Production
The foundational argument for deadheading is deeply rooted in botanical history. In Frank Kingdon Ward’s Riddle of the Tsangpo Gorges (originally written over 75 years ago), the legendary plant hunter offers this astute wisdom on page 166:
“In nature Rhododendrons rarely flower well for two consecutive years, because a good flowering period, if followed by a heavy seed crop, uses up all the plant’s energy; there is none left for building up next year’s flower buds. If the plant flowers well this year, but for some reason does not set seed, it may at the same time lay down resting buds and flower well the following year.”
This describes a biennial bearing pattern, where plants only flower well every alternate year. As Kingdon Ward observed, it is the production of seed—not the flowering itself—that acts as the critical drain on the plant’s resources.
The Competition for Glucose
Plants manufacture their own food from carbon dioxide in the atmosphere and water from the soil using the sun’s light energy. One of the first products of this photosynthesis is glucose.
A single molecule of glucose can only be used for one thing within a plant, creating internal competition. It must be rationed between:
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Non-flowering vegetative shoots
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New flowering shoots
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Developing seeds
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Root development
When food is directed toward seeds, which have a very high dry matter content, they consume a massive, disproportionate amount of the plant’s available energy reserves.
Natural Selection vs. The Cultivated Garden
Natural selection favors the plants best adapted to survive and perpetuate their species in a specific environment.
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In a shady site, “best adapted” might mean being the tallest, fastest-growing plant to reach the light.
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In alpine conditions, it might mean short, stumpy growth with the capacity to freeze, flower, and produce seeds quickly within a brief growing season.
Good old Mother Nature protects young plants in two ways: she delays flowering for several years so nutrients aren’t wasted when the young rhododendron needs to grow, and she disposes of the old through death to make way for the new.
However, nature must also preserve the species. To pass on a strong combination of genes, the plant invests heavily in sexual reproduction—producing flowers, nectar, and scent to attract pollinators, resulting in a massive wastage of seed. While this variation is essential for natural selection in the wild, gardeners want outstanding annual flowering. If we let the process continue to seeding, we are letting the plant waste precious energy.
Hormonal Inhibition and Nutrient Priority
The internal competition worsens when we examine plant hormones and resource priority, drawing parallels to commercial fruit orchards:
1. The Hormonal Brake
Orchardists routinely prune and thin their crops to get optimal-sized fruit. They do this because research shows that developing seeds release hormones that flow through the tree, inhibiting the formation of next year’s flower buds while promoting non-flowering shoots. While this exact process has not been formally demonstrated in rhododendrons, Frank Kingdon Ward’s observations were highly accurate: seed production halts future blooms. We see the same process in roses; if you do not remove the developing seed capsules (hips), flowering stops entirely.
2. The Nutrient “Pecking Order”
There is a strict priority order for nutrition use within a plant:
The Danger of “Over-Flowering”
It is often said that some dwarf lepidotes flower so profusely that deadheading them takes too much time. In reality, these are the exact plants crying out for assistance.
Many lepidotes run down and decline over time because they run out of energy by being too generous with their blooms. In sunny positions, varieties like ‘Kallista’ and R. nuttallii can literally die from over-flowering. They bloom profusely, set their seed, exhaust their energy reserves, and simply fail to grow back. Even early winter-bloomers like ‘Seta’ (which flowers in July) deserve to be deadheaded promptly to protect their longevity.
A Mindful Horticultural Practice
For generations, the act of deadheading has also been approached as a quiet, meditative partnership between the grower and the soil. Gardeners worldwide often reflect on the traditional Gardener’s Prayer during this hands-on care:
O Creator, bless this hands-on labor.
Grant me the patience to tend to what is fading,
The wisdom to remove what holds this life back,
And the faith to trust that in clearing away the old,
We make space for a more beautiful tomorrow.
Deadheading is a sound, scientifically verifiable horticultural practice that we should all actively promote. Developing seeds rob our plants of nutrients, stunt growth, and reduce future flower bud initiation. If you think un-deadheaded plants look unsightly, remember that aesthetics are only the beginning of the problem.
Frank Kingdon Ward did more than brave the wilds to find new species; he was an observant and insightful man. By following his observations and deadheading at our earliest convenience, we can enjoy regularly, beautifully flowering plants year after year.
References
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Primary Source: Davidson, Barry. The Merits of Deadheading. (Insights gathered from his tenure as National President of the Australian Rhododendron Society and established grower in Claremont, Tasmania).
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Historical Text: Cox, Kenneth, ed. Frank Kingdon Ward’s Riddle of the Tsangpo Gorges. Antique Collectors Club, England, 2001 (Originally written c. 1926, p. 166).