This year I have decided to give terracotta self-watering spikes a try. I am trying them because they are simple and they work similarly to the DIY ollas I have been using quite successfully for garden irrigation and especially container gardening for years.
How do terracotta self-watering spikes work? Terracotta watering spikes work because the clay they are made of is porous. This means when a spike is filled with water, from a bottle or reservoir, the pores of the clay slowly release water into the surrounding soil. The surrounding soil will wick water away from the spike into the root zone of your plant.
Moisture tension between the terracotta spike and the surrounding soil will determine how much water is pulled from the spike and reservoir. The dryer the soil, the more water is pulled. The wetter the soil the less water is pulled.
Soil type will also determine how much water is pulled from the spike and reservoir and how far the moisture will reach. For example, clay soil will not pull as much water or very far from the spike. Potting soil will pull water more quickly and further away from the spike.
Plants will also send out water-seeking roots that will attach to the spike and pull water as the plants need. As long as the spike is within reach, the plant should be able to find it and pull water from it. See also: Note: Example of Roots Attaching to Terracotta Watering Spikes