• Urban Arbors

What The Crocus?!

Updated: Mar 17, 2018

A common question this time of year is how the early spring bulb flowers survive those late snows in March and April.


The answer is there are a handful of adaptations and variations that contribute to our spring ephemerals hardy cold and snow tolerance.


  • One is just the inherent nature of being a bulb (or corm); because the main mode of reproduction is asexual through the cloning of the bulb, an the bulb is a specialized type of root and underground, the temperatures stay warmer where the this most critical function of reproduction occurs.

  • Snow is an insulator. Although the freezing temperatures may feel unbearable to you, the snow packed around the base of the flowers allows heat to build up close to the ground and underground. This is a likely pressure favoring shorter heights, and if you notice some of earliest spring flowers, you will also notice they tend to be just a few inches off the ground (e.g. crocus, snowdrop).

  • Some aboveground parts are built to resist external conditions and help to maintain internal temperatures above the air temperatures around them. For instance, if you look at leaves of tulips, you can see how thick and waxy they are. Crocus and snowdrops have leaves and petals that are small, making things like internal temperatures easier to maintain. Also remember the flowers, not being the fragile workers of reproduction, are not there for pollination as usual, they can be closed or delayed without risking reproductive success.



  • Some species can also manipulate the movement of water from areas vulnerable to freeze. The plant can move water out of its cells in cold conditions: remove the water, there's nothing to freeze, no ice forms inside the plant. You may be familiar with this adaptation on another types of plant: rhododendron (pictured below in a freezing temperature); rhods are famous for staying evergreen in temperate climates by moving water in and out of the cell so noticeable, you can watch the leaves fold down and spring back up...all winter long! Spring ephemerals generally tend to use this technique underground when needed around the roots, so there's no easily observed effect aboveground.



Several years ago, I heard a musing about the crocus being involved in WWII research searching to isolate chemical compounds in the crocus that could lead to better antifreeze. For years I've looked into this briefly when it pops into minds with the first showing of spring flowers. Unfortunately, I've never been able to dig up anything specific on the subject. The truth is all kinds of chemicals have been isolated and identified in the Crocus genus, but none have been looked at specifically for cold tolerance. Cold tolerance has, however, been looked at indirectly and correlated with toxicity in a species that is called crocus, but is not actually in the Crocus genus. This plant, known as autumn crocus (Colchicum autumnale) is technically in the iris family, and is also the source of an antimicrobial called colchicine. Colchicine is very damaging to cells and, while it works fantastically on bacteria, it can also shut down your cells; there's a fine line between medicine and poison. The higher the concentration of colchicine in the plant, the more cold tolerance the plant displays. And because colchicine already has such a long history with humans, I suspect it would likely be the chemical a military might look into for antifreeze possibilities.


Those are some of our favorite answers to this annual question! Do you know of another adaptation spring ephemerals use to survive in cold weather? Do you have any other spring questions about your garden?


Let us hear from you! Comment, or email us!

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