Pick the size and shape based on the plants root system. Shallow rooted plants, like leafy vegetables (ex. lettuce) and some herbs will need shorter Ollas so that the water doesn’t drain underneath the roots.It’s best to have ones that come with a cap. This prevents dirt, debris, insects and the like from falling into the vessel. It also prevents mosquitoes from breeding inside the Olla. If a premade cap is not provided, then a flat rock or some other object to completely cover the fill tube is necessary.They come in various types (ex. drip irrigation balls, handmade clay pots, DIY – usually terracotta flower pots, bottles, etc.). Choose the Ollas that best suit your planting area and plants.