Sunken Beds

Oh here comes the sunshine!!

With the hot summer sun and many months without rain, sometimes growing vegetables in the summer can be a struggle. To reduce the summer's effects, most locals move their vegetable gardens each summer to a place on their land that is cooler and wetter. Unfortunately, our summer garden is down in our valley, which floods most of the winter. So our summer garden stays more humid and cool at the start of the summer. But if you don't have a valley, you can do what the Moors did in this region over 1000 years ago and create a sunken bed.

What is a Sunken Bed?

Sunken beds are a type of permanent garden bed with features such as automated irrigation, trellises, and perennial companion plants. A permanent bed takes time but becomes productive and requires less maintenance. Other permanent beds include: The 'Back to Eden' wood chip bed, raised beds, lasagne beds, and Hugelkultur beds.

Sunken beds are the opposite of raised beds. Instead of building beds up, they are made below the ground. They were first developed by the agricultural geniuses' The Moors' and have more recently been adopted within the permaculture gardening world. In Portugal, these are mainly used for our summer vegetables as they have less advantage in the winter.

Advantages of a Sunken Bed

The soil in a sunken bed is considerably cooler than in a raised bed as the soil around the bed insulates it. Due to this, it will also hold onto moisture for much longer than any other bed. Like any permanent bed, it will have deep, rich, loose soil full of organic matter, which are the ideal conditions for vegetables to thrive. The bed also will have no perennial weeds. The weed-free, soft soil makes it very easy to weed, plant and manage.

Disadvantages of a Sunken Bed

Preparing a sunken bed is a lot of work upfront, but this is offset over time due to the beds being ready and easy to prepare and plant each year. You can enjoy the rewards for many years as these no-dig beds are easy to maintain and create an excellent yield.

Sunken beds can be prone to flooding in soils with poor drainage, which is why we often leave them empty during the winter, ready for an early summer crop. However, some years we use the beds for planting coriander, lettuce, and other short-lived winter salads.

Maintaining Sunken Beds

The primary maintenance is fertilisation. Our sunken bed's fertilising plan is the same as any other bed: A layer of well-composted compost at the start of each season and worm castings under each seedling at the time of planting—a weekly watering with worm extract or any other homemade liquid fertiliser. Then we mulch with straw, hay, woodchips or seedless weeds. We rotate the type of mulch each season. Weeding is also essential, and this can be reduced by heavy mulching. If the bed isn't used during winter, it can be dressed with compost and covered with cardboard. The cardboard will help kill any weeds that try to germinate before you plant your summer vegetables. This cardboard technique is beneficial and worth doing on all your vegetable beds that are left fallow (without plants), as it means beds are ready for planting in the summer. I love to have beds ready ahead of time. I avoid using plastic on beds as it creates heat that kills microorganisms, and over time it tends to break apart, littering the land.

How to make a Sunken Bed

Preparing compost. It would help if you had a lot of compost, so this should be started before digging your beds.

Design your sunken beds

Prepare wooden forms to fit the beds. Mark out the ground with the string. We suggest beds 100cm wide for easy access for weeding. Remove all the weeds from the area and add them to the compost pile

Dig out the topsoil and save this to one side. Dig down 30cm into the subsoil, ensuring the bottom is level.(If you are making a sunken Huglekulture bed, dig another 30 cm and fill this with logs. I will publish more on this in a future article.)

Place the subsoil onto the paths to raise them. Install drip irrigation; these should go under the paths and into the sunken beds.

Place the wooden forms and secure them by screwing them into a wooden stake in each corner and middle of the bed. We made sure that the top of the form was level and went 5cm above the level of the paths to allow for future mulch in the paths. If the planks were too thin, they did not function well, as the path fell into the bed under the planks. We don't have any slugs or snails here, but these wooden forms may attract them if you do. Also, we learnt from the first beds that placing cardboard along the sides of the beds and folding them into the paths saves on removing weeds later, so we did this for the last three beds.

Level out the paths against the forms.

Put the topsoil back into the beds and mix it with the ready compost that you are using, our chicken compost system, worm castings and composting worms.

Cover the compost with mulch—either green woodchips, hay, straw, woodchips, or cardboard. Hay will create more weeds but will build better soil. Straw in Portugal usually will be GMO and may contain a lot of chemicals. Put cardboard in the paths with a thick layer of woodchips for mulch. This is to keep weeds off the path, make it clear where to walk. Build any trellises that you need for climbing plants like melons, luffas or peas. The trellis should also work for vegetables that need support, like tomatoes. I like to have permanent solid frames so that the frame is ready for use each season.

In the six sunken beds, we planted two beds of tomatoes, one bed of cucumbers, one bed of peppers and eggplants and one bed of beans. In addition, in each bed, we planted various companion plants.

Summary

At Keela Yoga Farm, we have experimented with many permanent beds over the past six years, using different methods. I can tell you that anything planted in these no-dig sunken beds thrives during the summer more than anywhere else.

There are various ways to prepare sunken beds. They can be done with wooden forms to hold the sides up or without the forms. They can be dug more profoundly or more shallowly and have timber logs buried underneath (Hulglekulture). The most important aspect of my gardens is that they are easy to maintain. Having experimented with all the variations, I prefer long straight beds with fixed automated drip irrigation, nice supported sides and a permanent trellis.

Article by Laurence Manchee from Keela Permaculture Farm in Central Portugal. You can contact Laurence for Permaculture consultancy, join one of his Permaculture Courses or purchase composting worms or plants for your food forest.

Check our Youtube channel (Keela Permaculture) for a video about Sunken Beds. For feedback, suggestions or gardening questions that can be answered in future publications to info@keelayogafarm.com with the subject line reading 'Central Connects' www.keelayogafarm.com

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