Phenology

  • Published: Monday, March 2, 2020

Part 1

It’s springtime and whether you know it or not, you are probably exercising your phenological talents.  If you find yourself closely watching the progression of spring, you are most likely a genuine phenologist.

Phenology is the study of the influence of climate on biological events such as animal migrations and flowering in plants.  Horticulturists are very concerned with phenology, especially when woody plant species such as apples and peaches are involved.  This time of year, we closely watch the progression of budding and flowering, with an eye on the weather forecast.  We are all too familiar with orchard crop losses due to late frosts during full bloom.  The phenologist asks, “What environmental conditions control the development of buds and flowering?”  If we can understand the principles involved, there might be hope for controlling the timing of blooms and preventing crop losses.

Unfortunately, it is not an exact science at this point, although we discover more every year.  Temperature is an obvious factor that can speed up or slow down the bud development and time of blooming.  The rates of chemical processes are always temperature-dependent and warmer temperatures speed up the plant’s physiology.  Another factor is day length.  In addition, most woody species in our part of the world have chilling requirements to meet.  Even if you get warm days in early winter, the trees will not grow leaves or bloom, since their chilling requirement has not been met.  Once the requirement has been satisfied, they are ready to break dormancy when the weather turns warm.

Other factors can complicate phenology.  When I was working in southeast Missouri, we had a study at a peach orchard near Campbell that was looking at the effects of different rootstocks on bloom dates.

The rootstock came from varieties of peach trees that had been specially selected for growing good root systems.  In studies like these, the cultivar of peach that you want to harvest (called the scion) is grafted onto the rootstock.  One entry in the trial had an interstem, which is another variety, grafted between the rootstock and the scion.  This had been shown to delay blooms for up to 7-15 days in other states where it has been studied.

Our study did not find that much of a delay in peach blossoming, which was disappointing.  But that is what research is all about.  Try to find what works, and if it doesn’t, it will save the grower money by not going to the expense of grafting all those interstems.

In my next column, I will continue this discussion.  In the meantime, you might want to look at the National Phenology Network.  You can even sign up to contribute your phenological observations online.  Go to http://www.usanpn.org/

Part 2

In my last column, I discussed phenology, the study of the influence of climate on biological events such as animal migrations and flowering in plants.  This is especially important for horticulture crops such as apples, where buds that progress too quickly may be lost in spring frosts.

Ornamental species are good subjects for phenological studies as well.  One year in southeast Missouri, I noticed that the redbuds were very delayed in blooming, compared to dogwoods.  In all my years of watching Missouri springs, I don’t think I’ve ever seen a dogwood bloom before a redbud.  But it seemed to be happening that year, at least in Kennett where I was living.  Going towards Poplar Bluff, things seemed to be normal, with redbuds blooming and dogwoods on the way.  Phenology can be surprising, at times.

So I decided to conduct a short survey of other Extension specialists around the state.  Over around West Plains and Thayer, both redbuds and dogwoods were beginning to bloom, both about the same time.  The agronomist there had seen this in past years, when we had seen a late, cold spring.

Further north, things were closer to normal, with redbuds blooming and dogwoods not as far along.  But there was a lot of overlap that year, again probably due to the late, cold spring.  Some of the reporters didn’t think the redbuds were fairing too well in the Columbia area, others thought they were ok.

So what happened in Kennett?  After talking to several people, and taking a closer look at the trees, I believe that one of those cold freezes in March must have gotten the blooms.  This was somewhat surprising, since redbuds are fairly hardy, and grow much farther north. 

But as buds progress, they become much more tender.  And while they may easily survive a given temperature earlier in the season, if they have passed a certain point in their phenological progression, they’ll get damaged at that same temperature.  Apparently that’s what happened to our trees that year.

Last time, I mentioned the National Phenology Network on line.  If this topic is of interest, you can sign up to contribute your observations.  Go to http://www.usanpn.org/  for more information.

By the way, don’t add an “r” to phenology... phrenology is the theory that one’s mental capacities can be predicted by the shape of the skull, a popular theory in the 19th century, but I don’t think it enjoys as much favor today.

Writer: Timothy Baker

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