Wake Up Call!

It’s still mid-winter, but my spring-flowering bulbs knows what’s up - they are! With crocus in bloom and daffodils coming on strong, even the birds have sensed it and given out their call. How do they all know that spring is literally in the air? Breaking dormancy in Nature is quite observable in our natural environment, and it is especially so in our plant world. A dormant stage is necessary for conserving energy, preventing disease, and for protecting plants from predation. That dormant stage is now in transition, promising seasonal growth. 

Dahlia raisers are often admonished to check their stock while in storage. To me, this seems unnecessary and indicates a lack of confidence in the ability of establishing proper storage for dormant tubers. Once mine are divided and put to bed in my preferred medium (plastic bag filled with coarse vermiculite, then firmly packed into sturdy cardboard boxes) I never check, opening the boxes not until just before March tuber sales. It’s been my method for decades, and it’s not taking chances, as some may contend. I reckon that I lose one variety or another, but I never lose sleep over that. My iconoclastic approach works because it controls the three stimuli that break tuber dormancy - temperature, moisture, and light. 

It’s in that order that a dahlia’s dormant eyes awaken from their slumber. Once dahlia clumps are dug, growth eyes may develop swelling buds, but once in dry storage - at recommended temperatures below 45°F - those recede some within the tuber’s thickening epidermis. This makes identification of eyes on the rough corky surfaces of a tuber more difficult for some of us. The eyes will bud up once ambient temperatures reach room temperature (like 70°F) to encourage growth. Add higher humidity and then light, and watch shoots develop even in storage. Related geotropism stimulates shoots in their upward growth.

This is the botanist’s explanation: Dormancy is a physiological state induced primarily by a hormone called abscisic acid (ABA) that enters tubers from the stem during the season of tuber growth. Dormancy is characterized by a period during which sprouting will not occur even under optimal conditions. Dormancy is broken when the amount of ABA in the eyes decreases through metabolic breakdown to a level that allows the eyes to respond to conditions favoring sprouting.

Colloquially, we call dahlia roots tubers, but their proper term is tuberous roots. Both types are below-ground plant systems having fibrous roots (for nutrition uptake) and also swollen storage roots for starch and hormone processes. But the distinction here is that a tuber (think potato) has numerous lateral or axillary buds that develop growth, while tuberous roots locate their growth eyes only in the crown area next to the stem. We recommend removing all fibrous root hairs and thin elongated ends of tuberous roots (often called rat tails), since neither now contributes to the viability of the harvested storage tuber. 

For those desiring cuttings, the task of potting up tubers already is underway. If your aim is just to check the viability of the collection, it is recommended that - 4-6 weeks before planting - roots be placed into trays with plain soil above and below tubers and then located in a warm room, as suggested in this video link.

Martin Kral

Dahlia Talk Co-Authors Martin Kral and Dianne Reitan

at the 2023 ADS Show in Portland

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