School Project With Lima Beans - Knowledgebase Question

Calabasas, CA
Question by pfrancis
January 17, 2001
My son and 3 other kids had a project where they each received 5 lima beans and a 4-inch pot. The only difference was that each kid had to use a different type of soil. In our case it was topsoil. We were told to soak the beans for 4 hours and then plant, place in an east window and water with 1/4 cup of water every morning at 8 a.m. I told the kids that they needed to be in a south window and that it was too much water, to back off to at least every other day. Two of the kids had 5 inch tall seedlings, all of which sprouted by the end of 2 weeks. The other 2 (1 being my son) had nothing sprout. He did have one just begin to lift the soil but then nothing, it never popped up. The soil was crumbly and moist the whole time. What went wrong?

Answer from NGA
January 17, 2001


The interesting thing about science projects is that even though the seeds didn't sprout, there is a lesson to be learned. Lima beans (Phaseolus lunatus) have about an 80 percent germination rate. It's possible the non-sprouting seeds were not capable of sprouting, even under optimal conditions. Another common problem with failure to produce seedlings is planting seeds too deep. Seeds contain an embryo plus enough stored energy for a root, a stem, and two leaves to develop. If sown too deeply, the plant will run out of energy before penetrating the soil surface.

Beans germinate best at soil temperatures of 65-85 F. Once the seeds imbibe water (swell up), they need a constant source of moisture or they'll dehydrate and die. Moist soil is a must, but soil that's really wet will exclude oxygen, essentially suffocating the roots.

Beans do not need light to germinate, so unless sunlight was their only form of heat, it wouldn't matter whether they were placed in an east or a south window until after the seedlings had developed a second set of leaves. These are the leaves involved in photosynthesis (conversion of light into carbohydrates).

My guess, based upon your description of the project, is that the soil was too wet. Incorrect instructions were given for germinating the seeds - 2 ounces of water each day is excessive, unless the soil actually dried out overnight.

Hope this information sheds some light on the results of your experiment!

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