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What gardeners need to know about this flowering phenomenon

Have you ever noticed that certain plants that undergo dormancy flower before leafing out? This phenomenon, known as hysteranthy (hyster = after, anthy = flowering) is evident during late winter and early spring when many fruit trees as well as certain ornamental trees and geophytes (plants that grow from underground storage structures we call bulbs, corms, tubers, and rhizomes) come into bloom. The reasons behind this flower-followed-by-foliage sequence are varied, but all confer distinctive advantages to the plants in question.

I was inspired to write about this subject after seeing almond trees in bloom earlier this month. I learned that 25% of deciduous trees, including most Prunus species (almond, cherry, plum, peach, apricot, nectarine) are hysteranthous. While both leaf and flower buds of deciduous trees require a certain number of hours of winter chilling (during dormancy, the total number of hours below 45 degrees) to open, once this number has been reached, flower buds on certain tree species are more responsive to warming temperatures and thus open prior to leaf buds. All the mineral nutrients stored in the stems of such trees can then be channeled into the developing flowers without any of these resources being diverted to the leaves. 

Almond tree flowering before leaves appear. (Photo by Joshua Siskin)

It is important to remember that the sole purpose of a plant’s growth is to make seeds, the end product of a process that begins with flowering. Indeed, all the photosynthesizing activity of a plant’s foliage is directed towards providing the biochemical compounds needed to produce robust flowers that attract pollinators so that fruit and especially seeds can form. Ultimately, seeds drop in place or are distributed far and wide by wind or water or in the excretions of birds and various other critters that have feasted on the fruit.

In the absence of leaves, flowers will also be more abundant which means more insects will visit them and more pollination and seed formation will occur. Wind also affects pollination and will be more of a factor in blowing pollen from one flower to another without interfering leaves. Furthermore, flowers are more sensitive to water loss than leaves, so should a water deficit in a plant occur if warmer temperatures should suddenly prevail, the flowers will have already been pollinated and will not suffer from lack of hydration.

Pink trumpet (Tabebuia impetiginosa) and golden trumpet (Tabebuia chrysotricha), with brilliant pink and neon yellow trumpet flowers respectively, have been called the “eye-candy” of flowering trees.

Their growth habit is described as semi-evergreen since they are briefly deciduous before they bloom. In the tropics, this bloom period depends on the weather since a wet winter will delay flowering and a spell of dryness encourages it, as a trumpet tree may persist in forming leaves as long as soil moisture is high. Pink trumpet tree is the national tree of El Salvador, where tourism spikes during its bloom period. For this reason, predicting when pink trumpet trees bloom in a particular year has become a matter of economic interest in that country.

The coral trees (Erythrina spp.) that we grow here originate for the most part in South Africa, whose Mediterranean climate is similar to our own. These hysteranthous trees, in the manner of trumpet trees, also bloom at the onset of dry weather. In the case of coral trees, however, there is another advantage when leaves are absent at flowering time. Passerine birds, those that perch and make up 60 percent of all avian creatures, play a significant role in coral tree pollination.

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Finally, many geophytes, including certain crocus, squill (Scilla), and cylamen species, all orginating in Mediterranean climates, produce flowers at the end of the rainy season so as to remain hydrated as long as it takes to produce seeds before the stress of a long dry spell – which lasts through the end of the fall – begins.

California native of the Week: Bird’s foot fern (Pellaea mucronata) is perhaps the toughest among California native ferns. Another common name for it is birdfoot cliffbrake (brake and bracken are synonyms for certain fern species) and it does actually grow in cracks on cliffs, no doubt drawing moisture from underlying rock strata. The legendary Bert Wilson of Las Pilitas Nursery testified to this fern growing in rocks where the temperature “reached 130 degrees” during the summer and “where the December 1990 frost froze most things off this slope but the ferns looked better than ever.” Yet this fern has a delicate look that belies its reputation as an indestructible garden selection. It is resilient to drought and strong winds and will grow in full to partial sun, reaching one foot in height. You can acquire bird’s foot fern through Suncrest Nurseries, a plant grower near Watsonville that supplies a number of nurseries in Southern California. To find local retail nurseries in your area that would have access to this plant, go to suncrestnurseries.com and, when you get there, click on “Retail Sources” on the left side of the home page. 

Please send questions, comments, and photos to joshua@perfectplants.com.

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