Paying Attention to Phenology

Phenology is a fancy word for what we have been doing all along, paying attention to nature's cycles.

Reader Contribution by Lois Hoffman
article image
by Unsplash/Philippe Collard

Gardening and farming are a whole lot more complicated than just putting seed in the ground, tending it and reaping a harvest. Knowing when and what to plant, when and how to fertilize, how to control weeds and insects, how to manage too little or too much rainfall, temperature changes and so much more plays into it. And just when you have it figured out one year, it changes the next.

Yep, we need all the help we can get. We read farm reports, we listen to the experts, we learn from generations before us. In spite of all this, one of the best sources we can listen to is nature herself. Even though it seems at times that she has no rhyme or reason, Mother Nature always has a perfect plan and she reveals it to us through phenology.

A new word to my vocabulary, phenology is the study of cyclical natural phenomena and events, also known as the science of appearances. Plants, animals and insects don’t use a clock, but instead they use the condition of the environment to keep time.

It is basically taking note of when certain events happen from year to year. Natural events may not occur at the same time each year but they occur in the same order. For example, many die-hard mushroom hunters know that when redbuds and lilacs bloom, it’s time to look for mushrooms. These events occur together each year even though they don’t occur on the same dates each year.

orange pumpkins grouped together

Many universities devote studies to phenology, which is by no means new. It actually started in 1736 with the English naturalist Rober Marsham. His records, keeping track of the connection between natural and seasonal occurrences began that year and spanned the next 60 years.

Phenology may be the easiest and oldest way to see and feel when the world is changing around us. Data is gathered from multiple sources such as farmers, gardeners, fishermen and nature observers. It affects whether plants thrive or just survive.

The food supply depends on the timing of phenological events. Farmers and gardeners have long used this data to know when to plant and fertilize. Just watching nature from bud burst to bird migration is nature’s way of telling us when to perform certain tasks.

Understanding phenology and being able to put it to use also depends on understanding growing degree days, or GDD. As the number of GDD increases, interaction between the various species changes. So, basically, it is a weather-based indicator for assessing crop development, whether it be field or garden crops.

Without getting into the exact mathematical equations, GDD allows producers to predict plants’ pace toward maturity. Without other factors like amount of moisture, development rates of crops from the time a seed sprouts to maturity is dependent on air temperature. Because the development of plants and insects depend on certain amounts of heat, it is possible to predict when these things should occur during the growing season.

So, what’s the big deal of knowing this? Well, considering the price of fertilizer, insecticides and herbicides for both farmers and gardeners, it helps them to know when is the best time to apply to be the most effective. Herbicides and insecticides are only active for a certain amount of time so it is good to know when to apply them according to when the emergence of the weeds or insects that we are trying to control should be happening.

This is where GDD comes in. It can be used to decide the suitability of a region for certain crops and to estimate the growth stages of crops, weeds and insects.

Phenology events progress from west to east and south to north. This is called Hopkin’s rule and it means that events are delayed four days per degree of north latitude and one and a half days per degree of east longitude. It’s just saying what we have known all along: it gets warmer sooner in the south than in the Midwest, farmers get in their fields sooner in Missouri than in Michigan. This gives us a general timeline of how fast it is moving north and eastward.

Studying phenology tells us that many insects are emerging earlier than they did in the 1970’s because climates have advanced 2.5 days per decade.

Going a little further, we have phenological synchronization. Plants and insects respond differently to climate change which means that the timing of when a plant is flowering and when an insect is active could get disrupted. Some plants and insects change together and some do it separately.

green and red peppers on a cutting board

Paying attention to phenology can be an immense help in knowing when to plant, fertilize, apply insecticide and herbicide and, to a lesser degree, when to harvest.

When it comes to planting, many farmers and gardeners have long adhered to phenological signs as to when to plant certain things. Here are a few:

  • mushrooms pop when lilacs and redbuds bloom
  • when forsythia bloom, plant peas, onion sets and lettuce
  • daffodils bloom, plant beets, carrots and chard
  • wait for dandelions to bloom before planting potatoes
  • when maple trees leaf out, plant perennial flowers
  • when quince blooms, plant cabbage and broccoli
  • wait for apple trees to bloom before planting bush beans
  • when apple blossoms fall, plant pole beans and cucumbers
  • when lilacs are in full bloom, plant annual flowers and squash
  • when lily-of-the-valley blooms, transfer tomato plants to the garden
  • when maple leaves are full-sized, plant morning glory seeds
  • when bearded iris bloom, plant peppers and eggplant
  • when peonies blossom, plant heat-loving melons like cantaloupe

I will admit, I have not noticed these associations before but I will certainly be paying attention this year. Just imagine, following these signs and incorporating phenology with planting by the moon calendars, what an awesome garden that should be. Following nature’s clock and signs helps us to tune into the rhythm of life around us and truly get back to basics.

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