The best environment for any fish is one that closely matches its natural home. Unfortunately, it is rather challenging to provide that kind of environment in a small bowl. However, it's not impossible to make a bowl a reasonable home for your Betta if you are willing to make the effort. In climates that are warm year-round a Betta can do pretty well in a bowl; provided the owner changes the water regularly.
If you live in a northern climate, wintertime can present obstacles. Cold temperatures won't necessarily kill the fish outright. However, being subjected to long periods of cooler than optimal water temperature will stress the fish, rendering it far more susceptible to disease. Placing the bowl in a warmer location in the house will help, but the best option for those living in cold climates is to keep the fish in a heated aquarium.
Another option is to put a mini-heater in your bowl. Keep in mind that bowls are challenging when it comes to maintaining the proper temperature. It is easy to overheat, underheat, or have wide variances in temperatures. Frequent large temperature swings can be as stressful as constantly low temperatures. If you choose to keep your Betta in a small bowl and heat it with a mini-heater, make sure you monitor the temperature closely.
Does a Betta Need a Plant to Eat?
As for a plant, don't add a large plant to the bowl.
Although some report that Bettas will nibble on a plant for food, that is not entirely true. Bettas require meaty foods and are not plant eaters in nature. Yes, if they have no other food available, they will nibble on the plants. However, plant matter is not the ideal food for them.
Furthermore, it will be much easier to care for your Betta if don't have a large plant in the way.
If the bowl is large enough, a small live plant can be used, but make sure the plant doesn't block out the entire surface of the water. Bettas need to reach the surface regularly. Do not use live plants in a bowl that has only marbles for the substrate, as there will not be enough nutrients to support healthy live plant growth. A small plant in a small pot of substrate available in pet stores will suffice, and be easy to remove when doing routine maintenance.
Should I Clean Marbles on the Bottom If They Are There?
The glass marbles on the bottom of the bowl are okay and are easy to remove for cleaning. Keep in mind that food can and does fall under them, so be sure to clean them whenever you perform your regular water change.
Key Habitat Factors of the Betta
The key factors for keeping your Betta happy and healthy are; keep the water and bowl clean, feed your Betta a varied diet, and avoid letting the water remain cool (below 75) for long periods of time. Your Bettas appearance and behavior is a good yardstick to measure how he is feeling. A healthy Betta will be colorful, have a healthy appetite, and is active and interested in what is going on around him. A listless, inactive Betta that has a poor appetite and/or frayed fins is a red flag that something is wrong in the environment.