As discussed in a previous post, after a flower is pollinated it will produce seeds. The seeds may be inside a fruit such as a tomato. Ah, but how to get the plant to flower?
Some plants, such as the cocklebur, rely on daylight length to flower. This is called photo-period sensitive. According to Scientific American, tomatoes are photo-period neutral, so the number of daylight hours doesn’t affect them. However, at least one amateur gardening website claims that fewer flowers are produced with less than eight hours of sunlight. You could test this idea, of course.
Most of the following activities require two identical tomato plants. In an experiment where you are testing ONE idea (i.e. number of daylight hours), it is important to keep all other things the same. I will not be repeating this in each experiment. Just remember, treat each plant identically except for the feature you are testing.
Activity #1: Photoperiod
Put one potted tomato plant outside where it would grow normally in a field. Keep an identical plant inside in a dark closet until 10 a.m. and then set it outside next to the other plant. At 4 p.m. (6 hours), bring the closeted plant back inside. NOTE: Don’t let any light reach the closeted tomato plant during its dark period. Rather than the amount of sunlight the plant receives, photo-period actually depends on the number of dark hours. Even the slightest amount of light exposure during this period will reset the plant’s clock.
Tomatoes respond to nitrogen in either fertilizer or compost. They use the nitrogen to produce leaves and vines…but not flowers. That’s why it’s a good idea to plant your young tomato with adequate nitrogen to help it start growing…then stop. As long as the plant has nitrogen, it will continue producing more and more leaves but few or no flowers.
Activity #2: Fertilizer
Transplant tomatoes purchased in tiny pots into larger pots so they have room to grow. Give both plants a balanced fertilizer containing nitrogen when transplanting them into the larger pots (or use compost). Continue to fertilize one plant once a week but give the other plant no further fertilizer. How does their growth compare? Look for branch leaf, number of leaves, flowers.
Some tomato plants set flowers after a certain number of leaves have been produced. “Leaf” wasn’t defined in the otherwise scholarly study I read. It might have been individual leaves on a stem, or might have meant the number of stem offshoots. In addition, this study was published several decades ago and might not apply to new tomato varieties. At any rate, this is a fun project.
Activity #3: Count leaves until the first flower bud appears. More fun if you try two different types of tomato plants. Purchase them before they have begun to bloom because it’s super fun to wait for the bloom to appear. Question: why would tomatoes use this mechanism to decide when to bloom?
Apical growth can affect flower set. Apical refers to the end of the branch or stem. If you pinch off the end of a stem on a tomato, it will cause more greenery to sprout below the place where you cut, and can also force more flowers.
Activity #4: Allow one tomato plant to grow as it will, but pinch off the ends of some of the other plant’s stems and watch what happens.
Tomatoes conserve energy when they sense dry conditions. One way to conserve energy is by reducing flower production. That’s why growers recommend a steady source of moisture for tomatoes.
Activity #5: Water and Flowering.
How would you design an experiment to test whether watering a tomato plant has an effect on the number of blossoms produced? Design and carry it out!
Highly recommended: Draw and label the tomato plants on the experiments you choose.
Next Lesson: Make your own flowering hormone solution.
Comments or Questions: Camilla@Rumseyhouse.com
Science Without a Laboratory 