Generally speaking, if you want to grow plants, then one tent is enough, but if you want to harvest plants multiple times a year, then you need two, one for reproduction and one for growth.
There is also how many plants you have to plant at the same time. The plants in the grow tent cannot be placed very densely, which is not conducive to plant growth. If you need to plant a lot of plants, you need to buy a larger plant tent, or buy a lot of small plants.
2x2ft. Grow Tents- These can fit around 2 mature plants in 5-7 gallon pots.
2x4ft. to 3x3ft. Grow Tents- These tents can fit 2-4 plants in 5-7 gallon pots.
4x4ft. to 4x5ft. Grow Tents- These are able to fit 4-6 plants comfortably in 5-7 gallon pots.
5x5ft. Grow Tents- These tents can fit around 5-6 plants comfortably in 5-7 gallon pots.
DO I NEED A MOTHER PLANT TENT?
Ideally, yes. Some growers keep their mother plant in their veg tent, but, she has different environmental needs. Kept in a vegging tent, she’ll be taller than the other plants in your grow tent, so your light height won’t be right for her. She can also end up casting a shadow over nearby vegging plants so that they don’t get enough light. For best results, the mother plant really does need a tent of her own, or at least her own compartment in a multi-chamber grow tent.