Dustin Bajer, Pineapple Pit, Pineapple Fruit with Top

Creating Garden Microclimates

What a Poop Pit Can Teach Us About Garden Microclimates

I stumbled upon pineapple pits while researching old botanic gardens. The Heligan Garden in Cornwall, England, was created in the 18th century by the Tremayne family. The garden fell into disrepair after the First World War but was restored in the nineties. During reconstruction, a strange structure designed to create garden microclimates warm enough to grow pineapples was found amount the ruins,

To an 18th-century British gardener, a pineapple would have been an expensive luxury. I love two things about pineapple pits; that horse manure would have been everywhere in 18th-century Britain, and pineapples would have been almost nowhere. Gardeners at the Heligan Garden figured out how to turn an abundance of shit into a rare tropical treat.

Pineapple Pit Design

The pineapple pit has three trenches connected by permeable, hollow walls. Filled with horse manure, exterior trenches generated heat from decomposition. Excess heat travels through the hollow walls into a central glass-topped cold frame creating a tropical microclimate for growing pineapples.

Dustin Bajer, Drawing, Pineapple Pit, Creating Garden Microclimates
Diagram of a Pineapple Pit Used to Create a Tropical Microclimate

Creating Garden Microclimates

A microclimate is a part of your garden that consistently experiences temperature, wind, and precipitation conditions that differ from the rest of the garden. Gardeners instinctively use microclimates when planting tomatoes against a south-facing wall or water-loving willow in a low spot. Half the battle of putting the right plant in the right location is understanding your garden’s microclimates and soil conditions. But it’s rare for gardeners to go out of their way to create specific garden microclimates for their plants. Master creating garden microclimates, and you’ll improve the health and survivability of all your plants. It doesn’t even require trenches of horse manure – though it certainly could.

Create Sun Traps

A sun trap is any location that receives and holds onto the sun’s heat. Greenhouses and cold frames are classic sun traps, but any sunny location can be a sun trap.

Glazed surfaces retain heat, but naturally reflective surfaces such as white-painted walls or ponds can reflect sunlight toward plants. Pineapple pits are placed in sunny locations to take advantage of the sun and use glazing to trap the sun’s rays.

Slowly introduce new plants to sun traps so their leaves don’t burn.

Use Thermal Mass As a Heat Battery

Imagine a large rock in the middle of your garden. During the day, the rock absorbs energy (heat) from its surroundings and remains warm long after the day’s heat has passed. As the rock cools, it radiates heat to its surroundings creating a garden microclimate. Massive objects take a long time to cool down, but they also take a long time to heat up. The result is that thermal mass dampens temperature swings and can help establish consistent microclimates.

Rules of Thumb

  • All objects have mass. All mass stores heat.
  • The more massive an object is, the more heat it can absorb and retain
  • The more massive an object is, the longer it takes to change its temperature.
  • The darker the object, the faster it will heat up.

Sidewalks, buildings, rocks, fences, trees, planters and pots, decks and patios, and water barrels all have thermal mass. An overlooked source of thermal mass in the garden is soil – especially moist high-quality soil.

Made from brick, pineapple pits contain a considerable amount of mass. By sinking the pit into the ground, the earth becomes a source of thermal mass.

Hold Water In The Landscape

At the risk of stating the obvious, water is critical to any garden or landscape. Water is vital for all living things, but it’s also very heavy, making it an incredible source of thermal mass.

Water has another peculiar property – it’s about the only thing in your garden that changes states regularly. Counterintuitively, water releases heat as it freezes or condenses and absorbs heat as it thaws and evaporates. Adding water to your landscape is the ultimate way to create garden microclimates.

A pineapple pit wouldn’t require too much regular watering despite being glazed. Like an enclosed terrarium, water leaving (evaporating) from the plant leaves would condense and drip back down on the soil. But there’s a second source of water we’re overlooking. Decomposing manure, or any organic matter, gives off carbon dioxide, heat, and water – all things needed by plants,

How To Store Water in Your Landscape

Rain barrels and ponds seem like the logical place to start, but I disagree. Barrels and ponds are useful water harvesting tools, but the best way to store water is in soil and plants.

A garden with healthy soil can capture, store, and deliver water directly to your plants. Healthy soil is the ultimate rainwater harvesting technique and, thus, the best way to build a garden microclimate. Water will keep your garden cool on hot days and warm when the mercury drops.

The water-holding capacity of your soil comes down to the amount of organic matter it contains. Regularly mulching, densely planting, and building compost are all ways to add organic matter to your soil. And if you happen to have access to a cartload of manure, you’ll be off to an excellent start.

Observation and Iteration

Never underestimate the power of observation and incremental changes. As gardeners, we’re people of action – literally shovels-in-the-ground kind of folks. In my experience, the best gardens are the product of careful observations and time. Where are the sunny spots? Where is it dry, and where does the water sit? What might thrive there, or what could I do to create the garden microclimate I desire? Look for the larger patterns, try many small things, observe, tweak, and repeat.

If this is the sort of thing you enjoy, I’ve created an entire online course to help design an ecologically inspired garden.

Shrubscriber Ecological Garden Design Course, Online
Join the Shrubscriber Community to Access the Ecological Garden Design Course