Water is vital in the correct quantities . Plants get through water like we do. Fortunately the soil that they are growing in acts as a reservoir for water so they don't need regular cups of tea. However filling the reservoir three times just makes it overflow and doesn't compensate for weeks with no water. If they stand in water for too long, they get trench foot - some are more sensitive than others.
Plants compete with each other for light, water and nutrients .
If planted too close, then there will probably be a winner and a loser, or maybe just losers. You can help however by feeding and watering more frequently. This is what happens when plants are grown in containers such as hanging baskets and why containers are not an option for the reluctant gardener. Nature has produced the best competitors for any given environment . These are the xenophobic hardy natives who try to ethnically cleanse the area of our chosen interlopers.