Ollas work best with plants with adventitious root systems, which are fibrous root systems and above-ground leaves. The more roots in the subsoil, the better they'll grow and find the Waterpot olla water source.
Examples of such plants are tomatoes, peppers or capsicums, potatoes (and most nightshades), cucumbers, salad greens, kale, herbs, edible flowers, gourds, melons, squash, beans, peas, corn, flowering annuals, shrubs and fruit trees - this is not an exhaustive list by any means!
Plants with taproot systems (one primary root) like carrots, beetroots, radishes, parsnips are less likely to work with Ollas.
Ollas should not be used to sprout or germinate seeds. Seeds and young seedlings need to be surface watered until the root system has developed enough to reach the ollas for regular and efficient watering. This may take anywhere from 2 weeks to a couple of months. You will need to monitor this.
A thick layer of mulch placed on top of the soil is necessary to help regulate the temperature of the soil and minimise evaporation. How often you fill it depends on the plant (some plants are thirstier than others eg Tomatoes), the soil compostion and moisture levels, the weather and many other variables - just keep an eye on the water level every few days or week and the guesswork is taken away!
