A simple way to look at this is that an Olla distributes moisture to an area about equal to the radius of the Olla (i.e. the furthest distance from one side of the Olla's outside wall to the other side).The type of plant and its root system will determine how close you can plant to the Olla. As an example, plants like tomatoes with long root systems can be planted at the maximum moisture edge (outer limit of the radius) and have plenty of room to grow. Smaller plants like lettuce or decorative flowers with less aggressive root systems need to be planted closer to the Olla.There is no exact science as to the perfect distance for each plant. Part of the process of successfully growing plants using Ollas is trying different distances. Just remember the radius rule and do a little research about each plant's root system.