Tips for improving drainage in small gardens.
With the recent weather events that we have experienced, we have been asked for tips on improving drainage in our gardens to make them more resilient to heavy rainfall. The good news is that the measures we take to make a garden less prone to bogginess will also help it withstand periods of drought, so it's a win-win!
Our housing developments are built on hard compacted clay, which takes water much longer to seep through when it is dry and is prone to waterlogging when wet. To make matters worse, during hot weather, the clay dries quickly, becoming rock-hard and aquaphobic, meaning that when the heat is followed by periods of rain, water is not easily absorbed into the ground, causing it to pool and overflow our drains.
Add lots of rich organic matter.
You may have heard us say this before, improving your soil quality is so important!
Organic matter introduces many beneficial microbes that slowly break down organic matter. Over time the organic matter binds with the soil particles, forcing them apart and creating better aeration and space for water to seep through. Add organic matter to the soil by incorporating compost, mulch, manure, leaves, or other organic materials. We have a range of specially blended garden mixes developed specifically for urban gardens. View the range here.
Luckily there is a good selection of plants to suit various soil conditions, from always boggy, to damp to occasionally boggy.
For boggy soils.
If you have consistently damp or boggy areas, opt for wet-loving plants that absorb excess water and improve soil quality.
From left to right:
Papyrus King Tut, Iris sibirica, Selleria radicans,
Carex secta, Apodasmia similis (oioi grass), Carpodehus serratus prostrate.
For damp but free-draining soils.
These plants (with the exception of the Canna tropicana) are best suited to those shady sites on south-facing fencelines or under trees where soil takes longer to dry out due to the lack of light. Think forest floors or tropical underplanting. The Canna tropicana likes sunlight but prefers consistently damp soil.
From left to right:
Blechnum novae-zelandiae, Asplenium bulbiferum, Blechnum penna-marina,
Liguleria reniforms, Canna tropicana, Alocasia nigrescens.
For soil extremes.
For soils that experience more variation throughout the year, there are good options that can tolerate a range of soil conditions from dry to damp. These tend to be New Zealand natives that have adapted to our "four seasons in one day" type of weather.
From left to right:
Carex virgata, Phormium surfer, Libertia grandiflora,
Dianella nigra, Leptospermum scoparium, Leptospermum Burgundy Queen,
Hebe stricta, Arthropodium cirratum.
Build raised garden beds.
There are many benefits to having raised garden beds, but the most important is that it allows us to add premium topsoil. This soil is less compacted, providing good drainage and more space for the roots of your plants to grow deeper into the ground and access more nutrients.
At this stage, we can dig and turn the clay on which the beds are laid, creating more space for the new soil to blend and improve the old.
If you have a limited budget or building skills, raising the bed 15cm off the ground will provide some benefit by allowing you space to add compost and mulch, which will improve your soil over time. Big box retailers like Mitre 10 sell rolls of garden edging for the DIY gardener, or you could consider corten steel edging if you prefer a higher-end look.
However, we would opt for a minimum of 30cm for the best results.
Permeable pavers, stone and gravel.
A permeable hardscape has the ability to drain water directly through itself. This means the drainage system is built into the hardscape and requires less or even zero extra drainage features to keep the surface from pooling or flooding.
Permeable hardscapes decrease stormwater runoff, allow rainwater to permeate the ground, and help water your plants. To achieve permeable hardscapes, we can use permeable materials, such as stone, gravel or pebble, or lay the materials so that there is space for the water to run through.
The use of stone, pebbles and gravel to improve drainage has existed since antiquity! So there's no surprise that they are some of the most useful materials to use in the garden when it comes to porous hardscaping.
Additionally, the invention of honeycomb paving to secure the stones in place has made it easier to lay and more secure to walk on. Naturally, we're big fans.
Where the hardscape material is not permeable, such as concrete or porcelain tiles/pavers, it's important to lay adequate space between the tiles to allow water to run off. In the below example, we have cut a solid concrete patio into pavers and planted in between. Not only does it look good, but it also allows us to add more soil and increase our plant-to-hardscape ratio in the garden.
NB: Sometimes, the job calls for a drainage specialist, especially if water run-off occurs due to neighbouring properties. In these instances, we suggest reaching out to a drainage specialist or engineer or chatting with our team, and we can liaise with one on your behalf.
Our designers specialise in small urban gardens, terraced housing, balconies, and decks. If you are considering transforming your outdoor space, don't hesitate to get in touch for a free, no-obligation consultation.