Growing plants for your science fair project
If you grow plants from seeds:
How tall it will grow in a certain number of days?
How many leaves it produces?
How large the leaves are?
All of those are useful measurements of plant growth. You have to choose which you will use and then find a way to measure the plant growth.
For all plant experiments, once you decide what single thing you are comparing (such as growing in light or dark, with our without more water, different kinds of soil, with or without added plant food, in a quiet or noisy place, in heat or cold), then you have to make certain everything except the one thing you’re comparing is exactly the same. That way you can be sure that the changes you measure were caused by that single difference.
Make sure you let the experiment run long enough to get results. You can’t do a plant experiment at the last minute. It may take weeks for the seeds to sprout and grow. If you are doing an experiment where you are trying to do things to improve plants’ growth, remember that seeds contain enough plant “food” for the seedling to grow for a while with no outside food needed. So give them enough time to use up that “seed food” and start to use food from the soil or any liquid they may be growing in (if you are trying an experiment using aquaculture--growing in water with no soil).