Old 02-22-01, 02:19 PM
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My son is working on a science project for 6th grade. His assignment is to grow three avocado seeds in three different kinds of soil, and to compare the growth results. Any suggestions on how to start and soil? Need to start as soon as possible!! Thanks from San diego...
Old 02-22-01, 08:02 PM
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Let's start first with the avocado. Remove all the green flesh from the pit. Take a look at it. On one end, there will be a little light brown disk. This is the bottom. Plant the pit so that it is 2/3 buried, with the disk down.
How long will the project last? Avocados are a little slow to get growing. In addition, the cotyledons (the fleshy part of the seed) in an avocado are huge (that's why the seed is so big). These will nourish the young plant for quite some time regardless of soil conditions (this is why you hear of people growing them in water). Therefore, your son may not really see a difference between the soil types because so much of the plants energy/nutrients will be coming from the cotyledons for a long time. Here's an experiment - cut a seed open carefully. You'll notice that once you get it going, it wants to break in 2 sections (these sections are set, regardless of where you put your knife). Each one of these sections is a cotyledon. In between them is the embryo (immature plant). You can see tiny leaves a tiny root. You can see this in a peanut or bean easily as well. Notice how big the cotyledons are compared to other seeds.

I might advise your son to try to convince his teacher that a seed with a smaller cotyledon would yield better results. Beans are a great scientific plant. They sprout easily. So are lettuce, radish, oats. These all start easily and quickly. The smaller the seed, the smaller the cotyledons, and the faster you'll see any differences in growth, too.

As for soil types, I don't want to influence him too much (so he thinks about it a little), but we can talk about what plants need: water, nutrients, and sun. Since he wants to compare soils, he should make sure they all get the same amount of sun. He should think about what the properties of different soils might be: which might hold the most water? The least (or fastest draining)? Which one would have more nutrients? What would happen if you grew one plant in a low nutrient soil, one in a (naturally )high nutrient soil, and one in the low nutrient soil but added a fertilizer? Which kinds of soil would work best for this? Where would you find soil that has lots of nutrients in it naturally?

If he asks to do seeds other than avocado, it might help his case if he says he'll grow 5 or 10 in each soil. He can then measure their heights and average them (because, just like people, different plants have different heights and growth rates naturally). He can then compare the averages, and even chart the average height over time for each soil type!

Let us know how the project goes!

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