When considering a garden, the dimension of space is often neglected. Raised garden beds are used to add structure and definition vertically, yet few gardeners bother to excavate the ground underneath. A sunken garden, if properly implemented, can help add a surreal and beautiful dimension to the space where land meets water. 

What is a Sunken Garden?

The concept of sunken gardens dates back to ancient cultures, including Mesopotamia and Old Persia, with their “paradise gardens,” which featured long central basins lined with fruit trees. The famed Hanging Gardens of Babylon were said to feature sunken elements incorporated into its magnificent terraces. Nowadays, much of the splendor has been lost to the ravages of war and history, though there have been attempts to recreate it. 

The word “sunken” implies a gentle dip – mellow hollows in the landscape – not a drastic plunge into the abyss. It also conjures up poetic images of ponds strewn with lily pads, and to a degree, this is accurate. Often placed a foot below the main level, many sunken gardens consist of water features such as bogs or ponds. The sides are reinforced by robust walls to ensure that the soil does not cave in. Below are a few factors to consider when building your sunken garden. 

Basics of Creating a Sunken Garden

The notion of a sunken garden may seem prohibitively expensive and difficult to implement, privy only to the wealthy few, but it does not have to be overly elegant to be effective. With some careful planning, a simple plot of land can be transformed into a tranquil, multi-tiered retreat. Before you start, though, it is important to consult a landscaper to avoid disappointment later on. 

Drainage

When it rains, the excess rainwater will naturally gravitate towards the lowest level, and for this reason, many sunken gardens feature built-in ponds. If you plan on placing seating near it, good drainage is crucial to consider. 

Geometric Layout

Many sunken gardens are geometric in format, with a quadrilateral layout that centers upon a water feature and plants planted throughout. This is both intended to provide structure as well as be aesthetically pleasing to the eye. 

Robust Walls 

As mentioned, sunken gardens require robust walls to maintain the structure, holding up against the weight of the soil. The deeper your garden is, the more you need to focus on the structure – stairs or patio pavement may be needed for more elaborate constructions. Materials such as brick or railway sleepers work well, with posts installed along the edge to lend support.

Types of Sunken Gardens

Bog Gardens 

Bog gardens, known for its dense, vibrant foliage and carnivorous plants, are an exciting way to add biodiversity to your garden. Although bog gardens place an emphasis on dampness, they do not fare well in waterlogged conditions, leading to stagnant water and odd smells. Drainage is important – the addition of organic matter helps promote water retention and drainage. To replicate the natural environment of a bog, line a raised bed or planter with an impermeable layer such as a pond liner or roof liner, then fill with the necessary growing substrate. 

Sunken Waffle Gardens

Once used by Native Americans to grow crops, sunken waffle gardens are the inverse of raised beds, and because of its raised sides, it helps to converse water in arid regions. Each planting area is separated by “berms,” or mounded hills, creating a waffle-like design. Waffles are approximately 2 feet square and configured into a 3 x 4 shape. 

Sunken Patio Gardens 

This type of garden shifts the focus away from water features and lush plants to entertainment areas and seating arrangements. The walls are more deeply curved into the terrain, adding a dynamic, secluded feel to an otherwise flat area. A fire pit is a popular addition, but they are not recommended for windy areas. If you insist on a fire pit, be sure that the position is optimal – hedges or feature walls can help shield against prevailing winds. 

Mediterranean Pool Garden 

A Mediterranean-styled pool garden can provide a hypnotic respite from the heat, but it’s not the most economical, requiring intensive cost and skill. In this type of garden, elements such as shade, water, and fragrance intertwine to create an idyllic retreat worthy of an emperor. Night-blooming jasmine shrouds the air with fragrance as citrus fruits dangle from their branches, within reach.

Recommended Types of Plants to Grow

Depending on the type of sunken garden you choose, there are a variety of suitable plants to enhance the aesthetic and functionality of your space. 

• Evergreens and Boxwoods: If you are looking for a more controlled formality, rows of boxwoods help reinforce symmetry and create structure. Pines, cypress, eucalyptus are used to evoke the grandeur of the formal gardens of Europe.  

• Carnivorous plants: No bog garden would be complete with the stars of the show – carnivorous plants. Even mini bog planters offer opportunities to grow an assortment of sundews, pitcher plants, and butterworts.

• Aquatic Plants: For a water-filled garden, consider aquatic plants like water lilies, lotus flowers, and submerged grasses, which thrive in damp conditions.

• Fragrant Flowers: If you plan on dedicating your space to a sunken seating area, fragrance may be just as important as color. Classical flowers, such as jasmine, honeysuckle, and roses, are renowned for their fragrance and elegance. 

Palms: Many tropical plants instantly fill the space with their cascading, leafy greenery. Towering trees like bougainvillea, resplendent in magenta blossoms, are nice additions to a sunken garden, as are palms.