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Factors affecting flowering

Factors affecting flowering

Introduction: (Initial Observation)

Whether a plant is cultivated for its flower or its fruit, flowering is important to cultivators. Remember that all fruits start as a flower and to be more specific, a fruit is a part of flower that holds the seeds. More flowers means more fruits. Farmers and gardeners want to know the factors that affect flowering time and flowering rate.

By learning about such factors, they can make necessary actions to increase their production.

In this project you will investigate the effect of one specific factor on flowering of one specific plant.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Many different events, conditions and information may trigger a question that can be the subject of a science project. That is called an initial observation. The following is a sample of an initial observation that may give someone the idea of studying on factors affecting flowering.

Initial observation: I once heard that an increase in sunlight causes hormonal changes within the bodies of birds and thus influences breeding and egg laying. Chicken farmers and people in the poultry industry have known about the influence of light exposure on egg production for many years. To increase egg production, poultry farmers will often increase light exposure with artificial lighting.

I am wondering if we can change timing or increase the production of flowers and fruits by learning about the factors affecting flowering.

Information Gathering:

Gather information about growth and flowering of different plants. Read books, magazines or ask professionals who might know in order to learn about the factors that may affect flowering in a plant. Keep track of where you got your information from. Following are samples of information that you may find.

Factors that affect flowering vary among different plant species, and the exact mechanism behind this transition is not fully understood. Temperature, light, moisture, nutrients, and genetic composition of a plant are among the factors that may affect flowering.

When studying the effect of certain factors on flowering, you may grow several identical plants on a controlled environment and monitor/ record these flowering data.

  • Flowering time: Time required from planting to half-bloom.
  • Total number of flowers
  • Size of flowers (determined visually or by measurement)

Smart flowers?

Knowing when to flower is a critical ability that is closely tied to many issues related to development and environmental response.

The control of flowering time integrates many different signals and is a very complex pathway.

What does a plant want to know before it flowers?
-Season/photoperiod (day length)
-Light quality


Many plants cannot flower until they reach a certain size. Plant size is affected by temporal age, resources and speed of development (speed of leaf initiation).


Measuring the season by the day length (photoperiod) is a common mechanism in plants. Photoperiod often influences the flowering time of plants.
Long-day plants are induced to flower in conditions with >12 hours of light.
Short-day plants are induced to flower in conditions with <12 hours of light.
Day-neutral plants are unaffected by day length.

Light Quality:

Under constant light, the central oscillator still functions on a roughly 24 hour cycle.
When shifted to light/dark cycles, the central oscillator becomes “entrained ” to the light/dark cycles.


Many plants rely on temperature sensing to control flowering time as well. Winter annuals germinate in the summer, over-winter and flower in the spring. These types of plants typically require a cold treatment (of varying lengths and intensity) before flowering.

Scientists report that they have discovered a gene that regulates when plants flower and is critical for keeping a plant’s 24-hour clock running accurately.
The discovery adds a new piece to the still-unfinished puzzle of how plants regulate the transition from vegetative growth to flowering, and control their daily rhythmic activity. The discovery may aid agriculture, as farmers want to maximize vegetative growth from crops such as alfalfa and spinach, or control the timing of flowering and seed production.


Flower Time. Trees produce flowers at different times throughout the year, depending on the species. Flowering time identifies which season the flowers will appear on the tree. Other variables, such as weather or watering schedules, can also influence flowering time.

Note: The term flowering time can be used with two different definitions. The most common definition is the time of the year that a certain plant produces flowers. The other definition is the number of days from planting a seed to production of a half-bloom flower.

The Science of Phenology

Phenology is defined as that branch of science dealing with the relations between climate and periodic biological phenomena. In simple terms, it is the study of cyclic events of nature — usually the life cycles of plants and animals — in response to seasonal changes in their environmental conditions. Such changes may be variations in the duration of sunlight, precipitation, or temperature.

Phenology is a prime example of what important scientific information can be produced by simple observation and record keeping. All it really takes to be a phenologist are good senses for observation and a diary or journal to record them.

Growing seeds

For the beginner it’s easiest to use a commercial seed starting or germination mix. Anything that will hold soil and water and has holes in the bottom/lower sides to let water out is suitable for starting seeds. Shallow (3-4 inches deep) containers are best for easy transplanting. Rinse out and poke holes in the bottom of paper or Styrofoam cups, plastic pots, “6-packs” and cut-off milk cartons are all good. Plastic nursery flats are good for holding or moving many smaller containers, or for growing larger crops. Be sure to get flats without holes if you need to catch drainage water. Most of the vegetable seeds you will start inside should be planted 1/8 to 1/4 inch deep. Sow seeds in rows or “drills” 1-2 inches apart made with a knife or finger. Smooth soil out after seeds are in place. Another method is to scatter smaller seeds evenly over the surface and then sift or scatter a 1/8-inch layer of germination mix over them. Keep in mind that most seeds have a germination rate of at least 75%, so do not plant too thickly. Label the containers with the type of plant, variety, and date planted.

One of the greatest home gardening challenges is returning your poinsettia to its holiday glory. From mid-September until the first of December, you must expose the plant to complete darkness for at least 13 hours every day. Even turning on a room light for a few minutes several times a week during this dark period can prevent flowering.

The long nights induce flower formation as well as color changes in the modified leaves, called bracts. For at least 13 hours each day (for example, from 6 pm to 7 am), the plant must be in absolute dark at a temperature between 65-70°F. Exposure to any light during this period – even a room light that is turned on for only a few minutes – will delay flowering. Consider putting the plant in a closet or covering it with a light-tight box. If you cannot control night temperatures, 14 –15 hours of darkness may be needed.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

As you will see below, the specific plant that we have suggested for your study is a tomato. You may substitute the tomato with cucumbers, squash, pepper or any other plant that you like to test. Just make sure that you can find its seeds and it will grow fast enough for your project due date.

You may only choose one question or factor for your study. Your question can be one of the following or something new that you choose.

Following are some sample questions:

  1. Do periods of low temperatures affect flowering of tomato plant. Is a tomato plant frost sensitive?
  2. Do periods of high temperature affect flowering of a tomato plant. Is a tomato plant heat sensitive?
  3. Does the soil pH affect flowering of a tomato plant?
  4. Do daylight hours affect flowering of a tomato plant?

For the rest of this project guide, I choose question number 4 as the main question for this project.

Do daylight hours affect flowering of a tomato plant?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable is the daylight hours.

Dependent variables are flowering time and the number of flowers.

Controlled variables are water, soil, seeds, temperature, and all other environmental conditions.

Flowering time here is the number of days from planting a seed to production of a half-bloom flower.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following is a sample hypothesis:

Since outdoor plantation of a tomato often starts in mid spring to mid summer, I think longer hours of daylight contribute to its faster growth and flowering.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”


Introduction: In this experiment I will study the effect of daylight hours on flowering of a tomato plant. Since I am not able to modify daylight hours as my independent variable, I will use artificial light for this experiment.

Material and equipment:

  1. Tomato seeds
  2. Soil mixes
  3. 20 Pots (4 to 6 inch diameter)
  4. Timer switches
  5. Seed growth tray or any similar container

Consult your local nursery or garden supplier in selecting material. You may substitute the above material with what you can find at home. Final list of material that you use may vary from the above suggested list.


  1. Plant tomato seeds to get starters or transplants.
  2. Plant starters in about 20 small pots. One plant in each pot.
  3. Setup 3 separate artificial light cabinets and place 5 small pots of tomato plant in each cabinet. Adjust the timers for 10, 12 and 14 hours of day light. To simplify recording, name the cabinets A, B and C. Number plants in each cabinet from 1 to 5. So plant B3 means the plant number 3 in cabinet B.
  4. Water the plants every day while making daily observations and recordings. Record the following data in your journal.
  • Record the number of days till the first flower.
  • Record the number of days till the last flower
  • Record the number of flowers on the plants – twice per week

5.Record your data in a table like this

First flower table:


Plant Number First flower date Days after planting the seeds Average days in each group


Number of flowers table:

Plant Number Number of flowers on Sept 15th Number of flowers on Sept 18th Number of flowers on Sept 21st Number of flowers on Sept 24th

In the above table, substitute Sept. 15th with the first date that you observe a half-bloom flower.

Planting seeds

If you are new to planting seeds, the following information may be helpful.

Start the seeds indoors 6 to 8 weeks prior to the last frost date in your area.

Plant about 1/4 inch deep, in flats or small pots using sterile seed starting material. This will help to prevent soil born disease problems.

Water lightly and keep consistently moist until germination occurs. If the seeds dry out, they will die. You can cover the pots with a plastic bag to help maintain the soil moisture but be sure to remove the bag once plants appear. The tomato seeds germinate best if the soil is between 75-90°F.

Full light and cooler temperatures (60-70°F) will help to prevent the seedlings from becoming too leggy. After the seeds have germinated, place them in a location that receives a lot of light. A south-facing window should work. If this is not an option, a florescent lamp fixture rigged so that it is a couple of inches above the plants will work. If they do not receive adequate light, they will become spindly.

After the plants have their second or third set of true leaves and before they become root bound, transplant into 4 inch pots. This transplanting step will allow the plant to develop properly and promote root growth.


Harden off plants before transplanting outside. Be careful while transplanting so that you do not disturb or damage the roots too much. Young plants are very tender and susceptible to frost damage, as well as sunburn. Protect your young plants from hot direct sunlight. A couple of days of special attention like this will help to ensure a high rate of success.

Your young healthy plants will be ready for your main experiment in about 3 to 5 days after transplanting.
You can expect flowers about 30 days after starting your cabinet light experiment.









Light cabinet

Each of the five tomato plants in a group need a space of about 9 square feet (one square yard). The purpose of using a cabinet for each group is to separate the light sources such that each group has its own light timing. You can simply separate these groups using cardboards or curtains. It does not really have to be a cabinet for each group. You may also have to use wire cages inside this area to hold growing plants. This depends on the type of tomato plant that you use for your experiment.

Light Source

A four-foot long, two-bulb fluorescent light fixture is adequate for five plants in each group. 40-watt cool or warm white bulbs or grow-type tubes provide a good source of light. Do not use incandescent lights. Fluorescent lights should be kept 4-6 inches above the plants. Mounting them with link chains makes it easy to raise the lights as the plants grow.

1. Line plastic food box
with absorbent paper.


The lights should be kept on 10, 12 or 14 hours a day depending on the plant groups. An inexpensive hardware store timer will do the remembering for you.

If you are using a greenhouse and natural light for your experiment, you may set the timer to turn on your fluorescent light on sunset in order to increase daylight, so your fluorescent light will be a supplement to natural light.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Results of your experiments include your notes and your observations entered in tables. Use the sample tables provided in the experiment design section or design your own result tables.


You will need to calculate the average flowering time for the plants in each group. Write your calculations in this section of your report. Do not use calculations as a part of your display.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.