One of my hobbies

When I have time off I will take care of my plants. That is one of my favorite hobbies. I have a small playground [1] with different plants such as geranium, dahlia, rose, mint, ivy and so on. Moreover I like planting new plants with cuttings or seeds. I feel proud when my new plants grow up [2]. This hobby makes me feel calm and relaxed [3].

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1. A "playground" is normally a public area designed for children to play.  I imagine that it is a small "garden" in which you have plants.

2. "Growing up" is a phrase we associate with a child becoming an adult; I have not heard this term applied to a plant.  For a plant, we would normally say that it has "grown" or "matured".

3. Because "calm" and "relaxed" have the same meaning, it is not necessary to use both words.  Rather than using two similar words, you might simply say, "This hobby makes me feel very calm."