If you find watering your garden a never-ending chore in summer, then you should acquaint yourself with the ancient science of using ollas. Pronounced ‘oh-yah’, an olla or oya is a terracotta pot that’s buried in the ground and filled with water that slowly seeps into the soil. Sound simple? It is, and incredibly effective too.

My garden faces directly south and I live in one of the driest parts of the country so, as you can imagine, most of my mornings begin with watering the garden. Last summer was so hot and dry, I felt like I was spending half my life with a hosepipe in my hand so, with the super El Niño event predicted by several weather agencies this year, I’ve been searching for ways to cut the time I spend watering. Adding ingredients that hold onto moisture in hanging baskets made a big difference, and topping my patio pots with clay LECA pebbles drastically reduced how often I need to water them. And now I’ve added DIY olla pots to my raised beds and veggie patch, too, my watering time has halved.

But the best thing? My plants will stay hydrated while I'm on vacation, without me having to ask my neighbor for another favor.

How Do Ollas Work?

Because unglazed terracotta is porous, water can seep through the walls of ollas very, very slowly. Can you still remember that science lesson on osmosis? Well, when the soil outside the olla is dry, water is pulled through the terracotta to balance out the moisture levels. However, once the soil is saturated, the water stays in the pot.

Traditionally, an olla has a narrow neck, which sits just above ground level, and a bulbous body to create a large surface area for water to seep through. A removable lid prevents evaporation and garden critters falling in.

Do Ollas Reduce Water Use?

An olla not only acts as a moisture reservoir for a plant, it ensures water is used far more efficiently. When you irrigate your garden on a hot day, between 20% and 50% of the moisture is lost through evaporation. By storing water underground, ollas cut evaporation to almost zero.

Proof of an olla’s effectiveness lies in the millenia these terracotta vessels have existed for. Written evidence survives of unglazed clay pots being used to aid irrigation around 2,000 years ago, and terracotta fragments show ollas were commonplace among farming communities in arid climates where rainfall was scarce.

Are Ollas Good For Plants?

Ollas not only deliver moisture straight to a plant’s roots, but plants are clever enough to grow their roots towards the ollas! The underground terracotta reservoir also helps to maintain more consistent levels of moisture in the soil, which is far less stressful for plants than the rollercoaster of drought-to-flood conditions created by occasional watering with a hosepipe or can. For growing veggies and fruit, regular moisture encourages abundant, healthy harvests and reduces cracking, too. Well hydrated ornamental plants grow more flowers, with more nectar to feed pollinators, too.

Because you’ll reduce how much water gets splashed onto leaves when you irrigate using ollas, conditions will be far less favorable for fungal diseases to multiply.

Can I DIY an Olla?

It’s simple to make your own ollas if you have some terracotta pots such as these from Amazon. The bigger the pots, the longer they’ll last between filling. Seal the drainage hole with an exterior silicone sealant such as this from Amazon, then bury the pot in the soil with the rim just above the surface. For thirsty plants – for example, if you’re growing pumpkins for Halloween – use one olla for each plant.

Fashion some sort of a lid (a plant saucer is perfect), and weight it down if needs be. Then simply top up your ollas when you water.

Do Ollas Work With Potted Plants?

Ollas work in exactly the same way for plants in containers. However, in smaller pots, they take up valuable root space and reduce the volume of potting soil. In a pot, a better solution that works on the same principles is a terracotta watering spike. These are unglazed clay stakes that are sunk into the compost and hold the neck of an upturned bottle of water. Various sizes are available to suit different pot sizes and bottles.