Incredible days are approaching and the plants look very healthy

In this region of the world we are in spring and there are still cold and hot days, a fairly indecisive climate, even so my plants are growing at a good rate and I will be able to experiment with having small plants in the backyard.
One of my plants already has good buds but I would like them to increase in size. I am sure that the soil no longer has nutrients to feed the plant. I would like to read opinions about what chemicals I should add to the soil to have larger buds.

On the other hand, I have my small plants, of which when I woke up they were all with water, since my mother is a plant lover and I add water to them a little too much, even so I really appreciate the help.
I hope they increase in size these days, but I won't change their container yet because I'm waiting to see roots at the bottom of the pot.
Today I will go out and buy some soil and some nutrients because I will germinate the “White Grape” in a 10 liter container.