The Q&A Archives: Green Bean Science Project

Question: My son is doing a project--planting beans in plastic containers in potting soil. He is testing for the best growth by using variable watering solutions--plain city tap water and Brita (filtered water) and variable light sources--natural light in East window and artificial light (grow light). The question: we planted 4 seeds 2 inches deep and 1/2 inch apart in 4 containers of 4" of potting soil. We slightly dampened the soil (1/4 cup), planted the seeds, lightly watered on top of the soil (2 TBSP). Covered container with plastic bag. How often should we water the seeds? Shouldn't they germinate in 7 days?

Answer: Normally, they should germinate within 7 days if you are keeping them in a relatively warm spot (70-80F). However, you planted them pretty deep--2"--so it may take them a little longer. If the pots are covered in plastic, you might not need to water them until they sprout. (Be sure there are a few holes in the plastic, or it is loosely secured, so that air can get in.) Water lightly with a mister bottle if the soil surface looks dry, or if the pots have drainage holes, place the pots in a shallow tray of warm water for a short time. (Potting soil tends to be heavy and hold water, so be sure you don't overwater. Soilless seed starting mix usually are lighter and have better drainage.) <br><br>Just a suggestion, if you don't mind: Usually, whendoing an experiment like this, it's best to subject a group of plants to each treatment, rather than having one pot for each different treatment. If 6 plants in each treatment show similar growth characteristics, for example, then you can make some generalizations about their response to the variable. If you have only one plant, you don't know whether the growth pattern was just a "fluke", or due to other circumstances, or whether it truly represents a particular response to the variables. I don't know how large your pots are--if they are small, you might need to thin down to one plant per pot; otherwise, crowding might affect overall plant growth.<br><br>If I had to choose between the various light treatments, and the water treatments, I would probably choose light. I have a feeling there will be little or no measurable difference between the two types of water.

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