This centuries-old trick for keeping your garden well-watered might be the answer to your plants surviving a hot summer

It's hard to ignore the fact that the summers are getting hotter, and it's something that's worth factoring into your backyard planting. After all, what's the point of spending time and money investing in new plants for your garden, if they're all just going to perish in a heatwave anyway? 

You probably already know about the best time to water your garden when it's hot out, and about the sort of drought-tolerant plants that can stand up to high temperatures and dryer soil, but shy of installing an expensive irrigation system, it might feel like there's little you can do to help your garden plants otherwise when the mercury soars. 

However, there's an idea that's been around for centuries that's suitably low-tech that can really help to keep your garden soil from drying out, deeper in the ground compared to a shallow sprinkling, while avoiding waterlogging it. Have you heard of an 'olla'? If not, you're about to, while discovering why it's still relevant for a modern garden. 

What is an olla?

'An olla is an untreated terracotta vessel that is buried beneath the soil,' explains Karen Gibson (opens in new tab), a Master Gardener from Ohio and founder of Sprouted Garden. 'An olla features a spout which sticks out above the surface. You fill the olla with water via the spout.'

So you've got a terracotta vessel buried in your flower beds - now what? Well, an olla works thanks to something called 'soil moisture tension', where if the soil is dry, it will draw the water through the porous clay. 'The water then slowly seeps through the terracotta wall to the soil surrounding it,' Karen tells us. 'The roots of the plant in the container seek out that moisture source, and grow around it.' 

What are the benefits of ollas?

You can think of ollas as the original self-watering planter. 'Because the olla is buried beneath the soil, out of sunlight and weather, the liquid contained within avoids evaporation and provides a constant and reliable source of water,' Karen adds.  This is especially important during summer, when the surface of your beds or containers can become dry very quickly, ensuring there's enough water at the roots to keep your plants happy. 

The other great thing about ollas is that they won't release water if your soil is too wet, helping to avoid waterlogging. 'Ollas are great tools for keeping the soil in containers at the proper level of moisture, neither dry nor too wet,' Karen says. 

Best ollas for pots

Best ollas for flower beds

What plants benefit from an olla?

Ollas can be used to irrigate almost any kind of garden plants, but they work particularly well with certain types. They work best with plants that have deep-reaching, fibrous root systems, especially vegetable garden crops like melons, squashes and tomatoes. They're also great to plant alongside young trees to help them get established. 

However, ollas can still be used with shallower-rooted plants, you may just want to consider the size and type of olla you plant alongside. 

How do I use an olla? 

Ollas are relatively simple to use. Dig a hole the size of your terracotta vessel in your container or flower bed, and place your olla inside. You'll want to make sure the spout is one to two inches above the ground so that debris and earth doesn't wash inside (but you can also find ollas with lids, too). 

You'll need an olla per pot when container gardening, and in a flower bed or border, you'll need to position them strategically. 'A large bed would need several spread out in a pattern,' says Karen. Staggering them every 2-3 feet is your best bet, but you can also just choose to focus around plants that would benefit most. Also consider that the larger the olla, the bigger the area it will water. 

You just need to also consider access so that you can fill up your ollas as required. 'The spout or neck of the olla still needs to be accessible without stepping on low-to-the-ground flowers,' Karen tells us. 

Are there any drawbacks?

Of course, ollas aren't the perfect solution. Like large terracotta pots, they're often not cheap to buy, and if you're looking to plant across a whole flower bed, the cost may be prohibitive. 

If you plant ollas alongside trees, or plants with woody roots, you also run the risk of the trees roots breaking or cracking the olla at some point in the future. If you're having to fill your olla more regularly, chances are a crack has formed.