I recently found a product (http://www.theartofscience.eu/en/negozio/plantarium-activities-of-botany/plantarium-pet-plants-grow-in-gel/) where plants are grown in a gel soil that's supposed to contain nutrients to feed it. I was wondering if this is actually possible, and if it is I wanted to know if anyone here knows how to make that gel at home, because I live in Argentina and can't buy the product.
I am very glad you felt something was wrong! The only soil that should ever be used in pots is sterilized potting soil.
These water holding gimmicks go AGAINST great drainage. Fertilizer added to the soil means you'd better know what you are doing with fertilizer and include what it was that was added. Far better is to purchase potting soil without these gels or sponges and added fertilizer. Plain old potting soil medium has very little soil incorporated if at all. Perfect for plants in pots. People try to improve stuff by adding a gravel layer beneath the soil and above the hole at the bottom of the pot. That causes a perched water table.
Adding compost in the thought that compost is fertilizer just unsterilizes the environment. Compost is not fertilizer. Compost is not a soil replacement.
You have to add a balanced fertilizer with all three numbers; N-P-K If you are growing something for just leaves then a trio of numbers with N being higher than P and K is fine. If you want flowers or fruit, you have to keep N at least equal to P and K or better, N should be lower; 5-5-5 or better 3-5-4.
Always go half the directions and observe your plants. "Less is Best, More is Death and None is Dumb" concerning fertilizer.
Those gels and sponges that hold water in the soil are contraindicated for all plants. They promote fungus by holding moisture too long in the soil. Drainage also adds to aeration of the soil. As the water drains it PULLS the air into the soil. These gimmicks hold moisture in the soil and do not allow for re oxygenation. Products don't talk about this stuff when they are trying to sell...
I've seen this or something like this used in propagation labs, but that is a very limited circumstance and the new plants are quickly moved to more "normal" media once they make roots.
It looks like the inventor/manufacturer is trying to broaden the commercial appeal.
This is what I found: Plant gel is a water-absorbing polymer such as a polyacrylamide (frequently Poly(methyl acrylate) or Sodium polyacrylate). Don't know if those substances are available near you. If it provides nutrients, you'd have to include that when you mix it up. Interesting as a novelty, but I wouldn't put my favorite plant in it.