How Understanding Phenology Can Make you a Better Gardener

By Rich Hamilton
Published: May 18, 2023 | Last updated: May 18, 2023 03:01:12
Key Takeaways

Many gardeners start planning their garden in advance, mapping out the best time to start sowing, when they expect to harvest, and other milestones. Still, nature already gives us the most beneficial indications concerning the best times to plant various crops; we just need to know what to look for. This is phenology.

Phenology is a vital element of life. When a rose blooms, a bird builds its nest, or leaves begin to fall in the autumn, these things are signs that correlate with seasonal or climatic changes.

With phenology, you observe the plant and note the sequence of its life events. You then relate those to the weather. Climate, weather, and temperature all interact with the environment, influencing the plant, animal, and insect worlds.

Let’s look at how understanding phenology can help make us better gardeners.

Throughout history, humans have generally acted according to the predictable characteristics of seasonal changes. Today, the phenology of plants is a widely studied science. Modern phenology commenced in 1736 with the observations of the English naturalist Robert Marsham. His records of the connections between natural and seasonal occurrences span 60 years. A Belgian botanist named Charles Morren gave the phenomenon its official name many years later. The name phenology is derived from the Greek phaino, which means “to appear,” and logo, “to study.”


Phenology assists farmers and commercial gardeners greatly. It can help decide when they need to use fertilizers and pesticides and when they should plant if they want to avoid frosts. Of course, some aspects of phenology also go way beyond the boundaries of our farms and nurseries and help track and predict environmental changes due to global warming. (Read also: Integrated Pest Management for Small-scale Growers)

The most vital applications of phenology today include:
• Control of intrusive pests
• Optimization of planting, fertilizing, and harvesting
• Comprehending the timing of processes, such as carbon cycling
• Review of species vulnerability, populations, and ecological communities concerning ongoing climate change

How can Phenology Make you a Better Gardener?

corn seedlings


Phenology isn’t just valuable for commercial farmers and ecologists, though. Gardeners are often keen observers of the cycles of nature and can benefit from practicing phenology. The activities of birds and insects in the garden can let us know spring has arrived even if the sun isn’t shining and the forecast is for rain.

You may already be acquainted with certain gardening folklore. One example would be the saying that the perfect time to plant corn is when the leaves of the oak tree are the size of a squirrel’s ear! This, of course, is an early example of phenology.

We all know that planting corn has nothing to do with squirrels or oak trees. However, centuries ago, Native Americans observed that the soil was warm enough to prevent the seeds from rotting at this particular time. So, it was the best time to plant the corn and reap an early but bountiful harvest. (Read also: The Science Behind Companion Planting)

How plants and animals respond to weather conditions makes phenology a barometer of climate change and its impact. Observation of these reoccurring cycles can help the gardener pinpoint when to sow their crops and fertilize them.

We can use the seasonal migrations or winter hibernations of animals to mark plants’ critical life stages (phenophases). These would include sprouting, leafing out, and flowering. The goal is to establish a relationship between weather conditions and animal or plant responses.

How to Practice Phenology in your Garden

Suppose you do decide to practice phenology. Then it is essential to keep a log of events in your garden. Why? Well, because your garden will not necessarily include the traditional biological indicators, such as blooming lilacs and forsythia. You will need to use your garden environment to identify your own indicators.

Additionally, you must be aware that biological events do not necessarily occur at the same from one microclimate to another. They are influenced by various factors, including temperature, weather, sunlight hours, genetics, shadow, and proximity to other structures. (Read also: How to Use Microclimates to Your Advantage in Your Summer Garden)


Because so many environmental conditions influence the life cycles of plants and animals, the only accurate indicators of your immediate environment are those in your immediate environment.

It is a long-term commitment and will not help you overnight. Still, after a couple of years of logging and keeping records, you will notice a pattern in how seemingly unrelated seasonal events occur in relation to one another.

You will also notice these events don’t occur on the same date each year, but maybe earlier or later, depending on weather conditions, especially temperature. Nevertheless, your phenology log will soon become indispensable as a tool when you are planning your garden, and you will wonder how you ever managed without it.

Lilacs and other Phenological Indicator Plants

Lilac is a spring-blooming shrub often used as an indicator plant.

Indicator plants look for a particular pest and manage it in its most vulnerable stages. We can also use them to time the planting of vegetables, application of fertilizer, pruning, etc.

Cloned lilacs were chosen as the standard indicator plant when the U.S. established phenological observation networks in the 1960s. In theory, any differences in plant development from different sites would have to be due to environmental effects, not differences between the plants, because they were genetically identical.

The goal was to record the various development stages: first leaf, first flower, full bloom, and end of bloom. The observers could then note differences between multiple sites and any yearly differences.


Through observing lilacs, phenologists determined that you should plant crops like squash, beans, and cucumbers when lilacs are in full bloom. Vegetables that enjoy cooler weather, such as carrots, beets, and lettuce, should be planted when the first lilac leaves appear.

Squash and cucumbers should be planted when lilac flowers have faded.

Here are some other examples of common garden phenology:
• When early bulbs such as daffodils bloom, it indicates the ideal planting time for peas
• When late spring bulbs like irises and daylilies flower, plant eggplant, melon, peppers, and tomatoes
• When forsythia is blooming, crabgrass will be germinating, so treat it
• When crocus bloom, prune your roses
• When mock orange flowers, sow cabbage and broccoli for autumn harvest
• Plant your perennials when you notice the maple leaves start to unfold

Phenology for Insects and Disease

tent caterpillars infesting a crab apple tree

Phenology has other applications for the garden besides planting. Pest problems tend to occur at specific stages. Phenology can help determine when to take action against insects and various diseases. (Read also: Identifying and Dealing with Blossom End Rot)

• Apple maggot moths will be at their peak when Canada’s thistle blooms
• Mexican bean beetle larvae start their attack when foxglove blossoms
• Cabbage root maggots are present when the wild rocket is in flower
• Chicory blossoms indicate the arrival of squash vine borers
• Crabapple buds mean tent caterpillars

How Climate Change Affects Phenology

Changes in temperature and precipitation may alter phenology. The timing of events like flowering and animal migration are examples of some of the things that are most susceptible to climate change.

Phenology aims to identify the clues that precipitate events that may affect:
• The numbers, distribution, and diversity of organisms
• The ecosystem
• Food surplus or loss
• Carbon and water cycles

Across the globe, spring events are occurring earlier, and autumn events are happening later than in the past. Many types of plants are breaking dormancy sooner, and their life cycles are being accelerated. How plants and animals react can help us foretell whether their populations will increase or decrease. This makes phenology a primary indicator of the impact of climate change.


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Written by Rich Hamilton | Writer, Consultant, Author of The Growers Guide

Profile Picture of Rich Hamilton

Rich Hamilton has been in the hydroponics industry for more than 20 years, working originally as a general manager in a hydroponics retail outlet before becoming an account manager at Century Growsystems. He enjoys working on a daily basis with shop owners, manufacturers, distributors, and end users to develop premium products.

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