Re: what is the best plant and the best liquids to use on plant growing?

Rather than using human beverages, such as coffee, milk and 7UP, I recommend
testing products designed for plants such as fertilizers. 
There are dozens of brands of houseplant fertilizers that could be tested
(Hershey 1990). Using human beverages to irrigate plants would be too expensive
to be practical, and many will harm or kill plants because they contain excess
sugar or salt.

Plant experiments using different amounts of salt in the irrigation solution are
also very relevant because salinity is a major limitation to crop growth
(Hershey 1993, Hershey and Sand 1993). Cultivated plants are often harmed by
deicing salts.

There are a wide variety of seeds or plants that can be used depending on your
interest. Many types of vegetable or flower seeds work well. Dwarf marigolds can
go from seed to flowering stage in about 6 weeks if grown under a fluorescent
light bank (Hershey 1994).  
Other fast growers are chia, bean, and fast plants. Many houseplants are easy to
grow, can be readily propagated by cuttings and make good experimental plants
including wandering jews, piggyback plant, and devil's backbone (Kalanchoe
daigremontiana).

Five basics that are desirable for any plant growth experiment are replication,
control, weight measurement, statistics and adequate light (Hershey 1995). 
1. Replication means that you have more than one plant per treatment. Three
plants per treatment is the minimum, five is better. For example, if you were
testing four brands of fertilizer, you would have five replications for each of
the four treatments. 
2. Control treatments are needed so you can determine what the effect of your
treatment is. For example, in testing fertilizer effects on plant growth, the
control treatment would be irrigation with plain tap water and no fertilizer.
3. Many students measure only plant height, but that is often a poor measure of
plant growth. Measuring the shoot fresh or dry weight is a much better
indication of plant growth.
4. With replication, statistics can be used. Simple statistics helps determine
if differences among treatments are actual or just part of the variablity
inherent in living organisms. Simple statistics include means and standard
deviation.
5. Indoor light levels in winter are often very poor for plant growth. Growing
plants under fluorecent light (see last two references) will greatly speed plant
growth and improve the experiment. The more the plants grow, the more likely you
will be able to see differences among the treatments.

You can submit a request for a PDF file of any of my articles that are not online.

References


Hershey, D.R. 1990. Sleuthing the nutrients that make your houseplant grow.
Science Activities 27(4):17-20.

Hershey, D.R. 1993. Evaluation of irrigation water quality. American Biology
Teacher 55:228-232.

Hershey, D.R. 1994. Solution culture hydroponics: history and inexpensive
equipment. American Biology Teacher 56:111-118. 

Hershey, D.R. 1995. Plant Biology Science Projects. New York: Wiley


Hershey, D.R. and S. Sand. 1993. Electrical conductivity. Science Activities
30(1):32-35. 


Re: Why did the liquids kill the plants? Why did the tea do well?


Re: What is a good plant to test the effects of sugar or sweetener?


Re: Why will plants grow in Diet Coke and water and not other sodas?


Re: Can bean seeds grow with milk?


Re: will plants consume milk and orange juice?


Growbuckets and bottle reservoirs


Plant fluorescent lighting systems