Do you live in a region with heavy, compact soil? In these types of soils, growing anything food-worthy is a chore. You may find yourself tilling every year, as nutrients are depleted in the soil. Or you may find yourself adding amendments every season with little improvement.
Situations like these call for raised beds. Not only can you build your own soil on top of the hard-to-cultivate earth, but you also reduce issues like erosion, and most of all, poor drainage.
Raised beds don’t have to be expensive to fill, even when you want to have a high-quality, nutrient-rich medium to grow your plants in.
Here, we’ll cover the concept of building raised beds to increase the drainage capacities of your garden. We’ll start with an examination of the importance of drainage, and then discuss how you can develop a healthy raised bed garden that drains well.
Why Is Drainage Important?
You need good drainage in your garden for proper root development. Good drainage is concurrent with adequate soil aeration. Not only does this give plant roots room to move through the soil, but it also gives nutrients and microorganisms more mobility. A high exchange of nutrients results in overall healthy plants.
With good drainage, your soil has an opportunity to retain more moisture and nutrients, making them available to your plants longer.
This also prevents erosion that can come from growing food crops and tilling. In that same vein, the support that good drainage brings to gardens on slopes and hills is paramount!
Another benefit of good drainage is the ability to direct and collect any runoff. In many areas, having the ability to conserve water means you’re covered in times of drought.
What Causes Poor Drainage In Gardens?
The type of soil you’re working with is key to how well the garden drains. Heavy clay soil tends to hold a lot of water. If you have clay soil, you probably have poor drainage, and building raised beds will help you develop a better-draining garden.
At the same time, you don’t want highly sandy soil that drains so well that you have no nutrients to feed your plants. In this case, amend with water-retaining elements that will support healthy plant development. Raised beds assist with poor drainage in soils that hold too much water and those that can’t hold any as well.
Some plants require lots of water to grow healthy and strong, while others require very little water. Many plants are susceptible to root rot if they’re left standing in water for too long. Too much water is one of the main causes of dead plants. Too little water can have the same result but under a different set of circumstances.
How To Test Drainage
There is an easy way to test your soil to see how well it drains, and it’s better to do this before you build raised beds than to wait until they are filled. Dig a hole in any area of the garden that measures ten inches deep. Fill the hole up with water and wait for all of the water to soak into the ground.
Then, fill the hole back up with water again. If that water isn’t gone within approximately ten hours, the soil has very poor drainage and is not suitable for most plants.
Building Raised Beds For Improved Drainage
The most common way to provide proper drainage for plants is to create a raised bed garden. A raised bed is simply a structure that holds soil and keeps the plant off the ground underneath.
You can create a raised bed with various types of materials, such as blocks, brick, or wood. We are partial to Birdies Original Raised Garden Beds, made from Aluzinc-galvanized steel. The key is to make sure plants will sit at least 8 inches above the ground. In some areas, even more is better.
The soft soil allows roots to grow freely, and drainage will prevent them from rotting. After you’ve watered your plants a few times, you might need to add more soil to compensate for settling. A raised bed garden does take a little work, but the results make it all worthwhile.
Preparing Your Garden For Raised Beds
Grassy areas create more of a problem. If you’re building raised beds on a grassy area, remove the grass first with a tiller or a stirrup hoe. Then cover the bare ground with a layer of straw, mulch, cardboard, or rock.
If you’re using Birdies beds, before you fill your bed, lay down a 1/4 inch to 1/2 inch of gravel underneath. This allows for excellent drainage and protects the bottom of the bed. Another great benefit of using gravel under the bed is you won’t struggle with weeds throughout the season.
These prevent the grass from growing back up through the dirt and into your garden bed. They also prevent erosion that can occur from placing the raised bed directly on the ground.
While ensuring your beds are level isn’t required, it can help immensely with moisture retention and drainage. You can place your raised bed on the barrier of your choice and check it with a level to see if this is a worthwhile endeavor for you. Use existing soil, rocks, or even sand placed over your weed barrier to level your bed as needed.
Filling Your Raised Beds
The hugelkultur method involves building your soil on top of a layer of large logs, then smaller sticks and branches with leaves and compost filling in the gaps.
On top of all of that is usually a rich growing medium. One great way to save money while you build your raised bed is to hugel within the bed.
As the hugel breaks down, beneficial microorganisms and fungi cultivate the wood, and you have a continuously replenishing soil. One thing to remember, though, is your bed’s soil will settle about 6 inches in the first season.
You’ll need to have more to add on top when you condition soil for the next growing season than you would if you went with a bagged soil or composite.
Alternatively, you can fill your bed with a high-quality raised bed mix. Most soil companies have some blend that is formulated specifically for raised beds. These have the right drainage materials, nutrients, and water-retention materials you need to grow most veggies. You can formulate your own organic raised bed soil too.
While this is more expensive than using raised garden bed materials that are locally sourced branches, sticks, and leaves, it is definitely viable, and you won’t have to refill your bed as much at the end of the season as you would with a hugel or sheet mulching fill.
Improving Drainage In Raised Beds
So, now you’ve tested your raised bed soil. What should you do if you discover it doesn’t drain well? There are lots of different ways to improve drainage in your beds. Before you add anything to your garden, do a soil test to ensure you don’t overdo it.
To improve the soil’s structure in your bed, you can add compost. This offers some nutrients to the soil, as well as provides some acidity to more basic soils. Compost protects bare topsoil and helps with moisture retention too (should that be what you need).
Finally, compost can add girth to sandy or super light soil. Try not to add too much at once if you’re growing a variety of plants that may prefer less acidic soils.
Add some perlite to your soil if it tends to hold water more than is needed. Greensand can also assist with drainage and will also provide the garden with a source of iron, potassium, and magnesium.
One very simple way to improve drainage in your beds is to mulch around your plants. This retains moisture and also improves the soil’s structure as it breaks down.
Another interesting way to improve drainage in your raised bed is to sheet mulch directly on top of the soil. Of course, this is best done in preparation for the growing season, either before you’ve planted in your bed or between plantings.
You’ll need at least a couple of months for the mulch and compost to break down. Keep it moist during this time, then plant within.
You can use a hand tiller to till the soil and aerate it between your plants, ideally between seasons. If your hand tiller can’t break the soil surface, heavier-duty tools like a broadfork will work.
Insert the broadfork into the soil and gently lift. Ensure you’re not damaging the roots of existing plants in your bed. After you aerate the soil, you can add amendments if necessary.
You may wonder whether the till or no-till method is better. If your soil is already properly aerated, you can practice no-till gardening.
At the end of the season, leaving your roots in the raised bed and cutting the tops of the plants off for composting or dropping as mulch will improve drainage. The roots provide aeration to the soil. You can damage the soil structure by repeatedly removing plants by the root.
Cover crops for raised beds planted in cooler seasons prevent topsoil erosion. They also provide nutrients to the soil and give it a source of aeration and mulch if you’re chopping and dropping your crop.
As the cover crop grows in the soil, you feed beneficial fungi and microorganisms that improve the soil condition overall.
The soil temperature is regulated more effectively, and weeds don’t have a place to grow. Remember to chop your cover crops when they are 50-80% in bloom. This will prevent the germination of seeds that result from spent flowers.