Anyone who has planted a seed and has seen the whole process from sprouting to a young plant to a bush, shrub or a tree and then has enjoyed the fruit of love and labor can tell you about the state of the mind during the process. A plant takes so little but give so much more.
So we recommend gardening and planting and spending time with the plants at least a few days a week. This time allows you to get away from your electronics that always keep you plugged in, your physical work that you have to do versus what you want to do and your constant mental stressors. It brings you to this moment where you experience the growth, the blooming of the flower, the bugs and butterflies, and best of all, home grown organic food.
If you do not have a large enough space, start with a pot. It is not about how many plants but it is about the experience you get from even having just a single plant.