Raised Garden Bed Drainage: The Importance Explained

Raised garden beds undoubtedly improve the aesthetics of any backyard space. The tiered effect adds interest and color on different levels; it is much easier to work for those with mobility issues.

Raised garden bed drainage is relatively simple to achieve; it extends the growing season and yield of anything you choose to plant. Container planting always requires adequate drainage; without it, the soil becomes waterlogged, and the root system suffers.

Properly drained soil in raised beds is paramount for growing healthy plants, shrubs, and vegetables.

Why Raised Garden Bed Drainage is Important

Roots need to breathe; they carry oxygen and essential nutrients absorbed from the soil to all parts of the plant.

If water fails to drain sufficiently, it occupies the space meant for oxygen causing the plant to turn yellow. Over time the roots clog, leaves fall off, and the plant wilts and dies.

Sodden soil is a breeding ground for disease-carrying fungi and parasites. If left untreated, they attack the plants causing fungal root disease, something most plants cannot survive.

By their nature, gravel and rocks are misshapen; they don’t sit in neat tessellations, instead have small gaps between them.

These spaces provide room for excess water to sit as it waits to seep naturally away. The gaps also supply additional room for necessary oxygen.

Unlike soil, rocks don’t degrade nor compact over time. Once in situ, the drainage system will probably outlive the raised bed.

The Benefits of Raised Garden Beds

raised garden bed

We have little control over the soil quality in our back yards and have to do the best with what we’ve got.

  • Raised beds allow gardeners to create the perfect quality soil compatible with whatever they wish to grow. You are in control of the soil combination depending if plants prefer acidic or alkaline growing conditions.
  • Clay-based soil has poor drainage; sandy soil has better. Raised beds naturally improve drainage as it is easier to control.
  • The gardener gets to choose the bed’s location and plant accordingly, depending on the amount of sun/shade/shelter it expects.
  • The soil in raised beds warms up quicker than that on the ground. You can get a head start and sow seeds slightly earlier in the season.
  • The soil in a raised bed has better aeration; they are rarely trodden on during weeding and harvesting, so it doesn’t become compact. It holds the perfect balance of water and nutrition to promote healthy growth.
  • Weeds are less likely to grow; not only is there a protective sheet beneath the bed, but the raised lip also prevents seeds from blowing in on the wind.
  • Water and air have more freedom to move to enable the root system to branch out further and establish itself.

How to Add Drainage to a Raised Garden Bed

drainage for garden bed

The location for your raised bed affects the type of drainage you should consider.

If it is going on existing beds or lawn – some gardeners believe it won’t need drainage. The water automatically seeps through the yard’s soil.

However, if it is heavy, clay soil – the additional water may sit on top of the ground for long periods. It results in damage to the roots with a detrimental effect on the plant.

We advise always use drainage for raised beds.

Building Materials

building a raised garden bed with drainage

Railway sleepers are excellent for building raised beds; they are strong and have a long life expectancy. Scaffold boards are adequate height when growing vegetables but should be stacked higher for shrubs and perennial planting.

Wood should always be untreated; toxins from the tar can leach into the soil over time, creating an inhospitable environment for healthy growth.

Breezeblocks, gabions, and sheet metal are also viable materials.

Create a sturdy frame using wood nails or corner brackets. If you want it to double up as a seating area, ensure it’s around 50cm high for comfort.

Weed Prevention

Cut a sheet of landscape fabric a little larger than the area of the frame and lay it on the ground. It prevents perennial weeds and tree roots from breaking through while allowing sufficient drainage.

The Drainage

Place a layer of small rocks, pea gravel, or broken crocks across the base of the frame; rake it until it is relatively uniform.

They are inexpensive and available at all garden stores. Don’t throw broken terracotta or ceramic pots; smash them into smaller pieces as they offer an ideal drainage solution.

Compost

The best compost varies depending on what you want to grow.

Vegetables thrive in a soil-less compost; mix equal parts of organic matter with peat moss. Fill the raised bed to just beneath the lip before sprinkling in some organic fertilizer.

Most plants bloom when sown in a well-mixed combination of organic matter (well-rotted manure) sharp sand, and topsoil; The best ratio is 3:2:7.

Specialist alpine plants require a much grittier mix; always rely on the information stick supplied with each plant.

Once fertilized, give the raised bed a light watering and let it settle for 1-2 weeks, after which time you’re ready to plant.

Flower Beds Raised Above the Ground

If the flower bed is on legs or a concrete base, drainage stones are just as important to give the plants chance of survival.

Follow the same method, just omit the landscape fabric.

Maintaining Raised Beds

There is a delicate line between too much and too little water on raised beds. The best drainage systems should prevent water-logging, but follow these simple steps to know when it’s time to water.

  1. On a warm day, dig a thumb an inch deep into the bed (1.5” on hot summer days) If it feels dry, it is time to water.
  2. Take a lump of soil from the bed; roll it in your hand to form a ball. If it binds together, it has sufficient moisture. If it crumbles, it has dried out and needs water.
  3. Use a rain gauge to measure.

Water raised beds by hand; use a rose on the can to gently sprinkle across the target area.

How Much Water a Raised Bed Needs

Raised garden beds usually need more water and nutrients compared with ground-level beds.

How much and the frequency you should water raised beds is dictated by the season, the temperature, and what you’re growing.

Vegetable seeds need daily light watering until they have become established. Henceforth, weekly deep watering is sufficient, as long as they don’t dry out.

In temperatures of 60°F, most plants require 1” weekly.

In temperatures of 70°F, most plants require 1.5” per week.

Each 10° increase equals an extra 0.5” of weekly watering.

Morning watering gives young plants the whole day to drink and receive enough strength to cope with intense sunlight.

Late afternoon watering also works; there should be enough warmth of the day for the plants to absorb the liquid.

Never water at night; no matter how good the raised bed drainage is, water sitting in cold soil encourages fungus to harms the roots.

The best method of keeping raised beds constantly moist is to install a drip irrigation system.

Not only does this free up time, but it also targets the specific areas of the flower bed that need the most attention.

Final Thoughts

Raised garden beds contain the best quality soil. Hand-mixing the perfect combination of sand, compost, organic matter, and fertilizer tailors it to the optimum growing environment for your chosen crop.

With the addition of stone or gravel drainage, the soil obtains proper aeration, and roots receive the perfect balance of water, nutrients, and oxygen for a bumper crop.

Anthony Marsh
Anthony Marsh is a writer with deep roots in the soil of western New Hampshire. His first experiences with gardening were at the age of 10 where his parents allowed him to plant and cultivate his first vegetable garden. Twenty years later he’s continued with his passion for gardening and actively rescues abandoned plant life.