How to Turn an Old Concrete Pool Into a Garden (Without Building a Swamp)

The Dilemma

A homeowner recently asked:

We bought a house with an old above-ground concrete pool and want to fill it in to create a kitchen garden, but I am worried about drainage and what kind of substrate to use.

The GardenOwl Diagnosis

The Scenario

I see this all the time. You buy a property with an old, unused concrete pool and think you have just inherited the ultimate raised garden bed. The stone walls provide incredible visual weight, the footprint is massive, and you are already picturing sweeping masses of culinary herbs and structural vegetables.

But before you order ten dump trucks of topsoil, you need to understand the physics of what you are dealing with. If you fill a sealed concrete basin with dirt, you are not building a garden. You are building a swamp. This is a textbook example of The Bathtub Effect Syndrome. When you place a highly porous medium, like garden soil, inside an impermeable substrate, like a concrete pool shell, water has nowhere to go. It pools, it stagnates, and it rots the roots of everything you try to grow.

The Trap

When homeowners ask how to handle pool conversions, someone will inevitably offer this terrible advice: "Just drill a few four-inch holes in the bottom for drainage".

Do not do this.

If you drill a few small holes in a concrete basin of that size, you are creating massive hydraulic bottlenecks. According to basic soil health and drainage principles, water moving through a soil profile carries fine particulate matter. Within two seasons, those small holes will completely plug up with silt and migrating soil. Once they clog, you are right back to owning a giant concrete swamp, and the only way to fix it is to dig out fifty tons of wet mud.

The Solution (Deep Dive)

To do this right, you need to view the project through the lens of structural engineering first and horticulture second.

1. Total Floor Annihilation You need a local demolition or excavation contractor to get in there with a jackhammer and completely shatter the pool floor. You do not need to haul the concrete away, but you must break it up entirely so water can naturally percolate across the entire footprint without bottlenecks. Maximum native earth contact is non-negotiable.

2. Manage the Rubble and Voids A smart move is to have the demolition crew knock off the top foot of the concrete walls and toss that rubble into the deep end as fill. However, if they just dump dirt over chunky concrete, you are setting yourself up for failure. As water moves through the profile, it will wash the soil down into the empty spaces between the concrete chunks. This creates massive, unpredictable sinkholes on the surface that will rip apart whatever beautiful garden structure you build on top. To prevent this, whoever manages the rubble needs to wash clean gravel down into the voids before any soil is added. If you have ever wondered Why Your Dirt Path Turns Into a Swamp (And How to Fix It Permanently), it is almost always due to this exact failure to separate aggregates from topsoil.

3. The Soil Stratigraphy Do not waste your money dumping expensive premium garden soil all the way down into a six-foot deep pool. Vegetable roots only care about the top two feet of the soil profile. Have your contractor haul in bulk, inexpensive clean fill dirt for the deep space. Save your budget for a premium topsoil and compost blend, and use that strictly for the top twenty-four inches where the biological magic actually happens.

4. Avoid the Sunken Garden Trap It is tempting to only part-fill the pool and create a romantic, sunken garden. I strongly advise against this for two reasons. First, sunken spaces trap cold air. They create micro-climates known as frost pockets, which will significantly shorten your growing season, a fact you can cross-reference with any regional data from the USDA Plant Hardiness Map. Second, maintaining a kitchen garden requires moving heavy materials. Hauling a wheelbarrow full of wet compost up and down a set of stairs is a massive, unnecessary headache. Fill the pool completely and keep your garden flush with the surrounding grade.

The Diagnostic and Visualizing Safety Net

Before you hire anyone to start moving dirt or swinging a sledgehammer, you need a plan that respects the heavy visual weight of those existing stone walls. You want your new layout to complement that structure with sweeping, connected masses of plants rather than a scattered, polka-dot mess of isolated vegetables.

This is where you should upload a photo our Exterior Design App. It acts as a structural blueprint and safety net, allowing you to visualize exactly how flush beds, pathways, and plant massing will look in that specific enclosure before you spend thousands of dollars on a layout you might regret.