It is important for potted plants to be fertilised regularly. It does not matter whether they are placed on the balcony or inside the house. The space of roots in the pot is limited and they cannot get nutrients by themselves. That is why they rely on the addition of extra nutrients. This is not much effort since it can be combined with the watering process.
Just add some liquid fertiliser to the watering can. Apply the fertiliser according to the recommendation on the packet. This process can be repeated weekly or bi-weekly. You can find fertilisers for your balcony plants in DIY shops, garden centres or specialised stores.