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How Deep Should a Raised Garden Bed Be?

Deep-Raised-Garden-Bed-featured-image

Some areas have poor soil, making the planting of crops difficult. If you plant on such soil, the crops will not perform well for several reasons. It could be that the soil is too compacted.

When soil is compacted, it has a reduced ability to receive water, sunlight, and nutrients. Also, the soil may be damaged due to construction or other factors. Therefore, there is a need to find other alternatives.

This is where raised garden beds come into play. A raised garden bed stands free off the ground, usually constructed a little above the soil under it.

The garden bed contains soil that you can modify to accommodate different crops for better growth.

The depth of the garden bed does not need to be more than twelve inches. You can measure it out to be between eight and twelve inches.

However, if you must go deeper because of the type of crop you are planting, it must not exceed eighteen inches.

The advantages of using raised garden beds are numerous, including difficulty for pest and weed invasion, a better plant habitat, and easy maintenance.

An article of interest: How To Start A Garden

Crops and Soil Depth

Crops-and-Soil-Depth-Raised-Garden-Bed

While the most popular soil depth for a raised garden bed is 11 inches, the crop you choose to plant will determine the exact depth.

Some vegetables require more depth than others, and the garden soil type also depends on the crops.

Plants such as broccoli, corn, cabbage, arugula, and chives need soil depth between 12 inches and 18 inches. Other crops that may need the same depth include lettuce, radish, garlic, strawberry, celery, onions, and spinach.

Plants such as squash, beans, cantaloupe, peas, potatoes, beets, and kale require soil depth between 18 inches and 24 inches. This category also includes turnips, pepper, cucumber, carrots, and eggplant.

Some plants need deeper soil to thrive. They include parsnips, watermelon, rhubarb, okra, and artichoke. These plants require soil depth between 24 inches and 36 inches to grow. This category includes pumpkin, asparagus, tomatoes, and sweet potatoes.

Summarily, know the type of crops you desire to grow in a raised garden before determining the soil depth.

If you stick with the standard 11 inches for a bed, crops that require more depth will do poorly.

Constructing a Suitable Raised Garden Bed: Factors to Keep in Mind

Building a raised garden bed is a critical process, as you will need to plan the details to ensure you get the best results.

However, there are several factors to remember as you plan the construction to ensure you get the right results.

  • Site and Plant Selection

Where you choose to set up the garden bed will determine the type of plants to grow. Some plants require lots of sunlight, while others do not need so much of it.

That means that if you choose plants with high sunlight needs, the garden bed site must be in an area with adequate sunlight. 

If that is not within your power to achieve, you may want to look for a site that gets a good amount of morning sunlight.

However, if all you have is a shady area, you may want to use artificial lights to achieve the same results. LED lights strategically positioned can provide the light needs of the plants.

Another option is to grow only plants that do not require a lot of sunlight, such as cool-season vegetables. While considering sunlight supply, it is also crucial to consider airflow.

Fungi-driven plant diseases thrive in areas with poor airflow. At the same time, do not site the garden bed in an area that is too cold or tends to have frost pockets.

  • Garden Bed Design

Garden-Bed-Design

The next factor to consider is the design of the garden bed. This point is also where you determine the depth of the garden bed.

The beauty of raised garden beds is that you can design them as a formal or informal type and site them in any area of your yard. An informal design can fit anywhere without looking odd.

If you choose a rectangular bed with low brick wall edges and filled with pruned boxwood, you can set it in your front yard because of its formality.

However, a bed with edges with an irregular shape made with stone is more informal. Therefore, it may fit anywhere else on the property. There is also the bed size to consider when deciding where to place it.

Whatever edging you choose to use in the design, remember that the material determines how well the soil holds. 

Additionally, the higher the garden bed, the easier and better the maintenance process.

You can choose to use mortared stone or brick as the edging material. Stone or brick is usually the more attractive choice and is durable and stable.

If you are going for this option, it is important to note that stone is usually expensive. The same is valid for brick.

Other less expensive edging options include timber, railroad ties, or metal strips.

  • Drainage

The drainage option of a raised garden bed is a crucial part of the planning. If the soil in the bed does not properly drain, the soil becomes too wet to allow oxygen.

Consequently, the plants will not thrive and begin to die. Furthermore, wet soil encourages diseases that kill the plants.

Therefore, choose the right site and soil for the raised garden bed to encourage proper drainage.

Loamy soil is ideal, but if all you have is clay soil, make one-third of the soil out of coarse sand to prevent waterlogging. 

You can also opt to construct special drainage systems, especially if the bed is sited in a wet area.

As much as possible, keep from setting it in a marshy place because of the water in such places.

A simple choice is a French drain, which is a narrow trench with coarse stone in it. It usually channels the excess water from the garden bed area to a lower area.

  • Irrigation

Irrigation-Raised-Garden-Bed

How you will supply water to the plants is an essential factor to consider. It is during the design of the garden bed that you must determine the irrigation method. Watering by hand is an ideal method because of the careful attention you will pay.

However, it is a stressful process to water the crops, especially if you have multiple garden beds. Another issue is knowing how much water to use and when is the right time to do it.

An automatic sprinkler can do the job of watering the garden bed without so much effort from you.

The downside is that it wets the leaves and foliage, creating an excellent breeding ground for disease and damage from salt.

Also, its automatic system can increase the water in the soil if it waters the plants even after rainfall.

You can choose any irrigation system based on planted crops and available beds. If you have crops with different watering needs, divide the garden beds into watering zones. A sprinkler system with several heads can work or consider using emitters.

However, remember that emitters may easily clog if the water is not clean and are vulnerable to rodents.

Several irrigation options are available to you, and you can use professional services to determine the most suitable choice.

Appropriate Height of a Raised Garden Bed

Appropriate-Height-of-a-Raised-Garden-Bed

If you want to get adequate drainage for your garden bed, 11 inches is an ideal height for it. You can add 12 extra inches of soil under the bed to make for better crop growth.

The advantage of using this method is that the soil gets warm earlier than usual because it is raised in a bed.

Therefore, you can begin your planting season earlier and have a longer growing period.

The height of the garden bed also determines how much you will have to bend over when tending the plants.

If you water the plants yourself, a higher garden bed makes for less bending. This simple fact is essential if you are older or do not care much for bending.

So, you may want to exceed the usual 11 inches height for the bed; consider raising it to a height of eighteen inches.

Taller garden beds will need more depth. That means having more soil, which may not be ideal in the long run. The soil compresses the more you water it, making it denser.

The more soil there is to water, the heavier the bed becomes. Eventually, it puts pressure on the bed and causes it to bow outward. In such a case, s cross support may be handy.

Constructing a Suitable Raised Garden Bed: Steps

If you want to construct a raised garden bed from scratch, it is crucial to know the proper steps to take. Depth is an essential part, but it is not all there is.

You must know how to lay the perimeter, uproot vegetation in the area, set the edging up, and install irrigation, among other steps.

  • Perimeter Layout

Map out the area where you need to build the garden bed. Straight-lined beds are easier to map out because you can use strings or stakes to make an outline.

If you are building an ornamental raised garden bed, it may be a little challenging to outline.

Use flowing rather than tight curves if ornamental to make for easier outlining and maintenance.

  • Uproot Vegetation

The site for your garden bed may have existing vegetation. You cannot construct the bed with the vegetation under it, so removing it is crucial.

Use the right tools to cut down trunks and stems before uprooting the roots. If there are perennial crops, a herbicide can prevent them from regrowing under the bed.

  • Set Up the Edging 

How you install the edging for the garden bed depends on the type of material. If you are using metal for the edging, the usual width is 4 inches to six inches.

The length varies based on the size of the bed. You can connect them using stakes inserted through notches that overlap.

If you use cinder blocks or bricks, you need a concrete footer about 16 inches wide and 10 inches high. The footer acts as the base or foundation to hold the wall of the bed.

Allow the footer to cure for about 3 days after pouring it, then wet it to apply about an inch of mortar about two feet down the slab. Mortar works for brick edging; cinder blocks may not need mortar.

However, you may need big stones if you build the edging with stone. As a result, you need equipment to lift large stones to avoid injury.

Stones will require mortar to secure them, and when all the stones are set on mortar, you need to give them time to set. 

You may need professional hands to construct this edging because it may be too complex if you do not have the skills.

Landscape timbers are also an excellent material for constructing the edging. So, consider that option instead of stone if you want to do the job yourself.

Set-Up-the-Edging-Raised-Garden-Bed
  • Set Up the Irrigation 

The type of irrigation system you install will determine whether or not you put the soil in the bed before or after installing it.

If you use an automatic sprinkler system or trenches, it goes in the bed before adding soil. Other irrigation methods can come in after adding the soil.

How to Maintain a Raised Garden Bed

Mulch plays a vital role in how a raised garden bed fares. Mulch ensures the roots stay cool when the weather is hot and prevents dehydration by keeping the water from evaporating.

It also improves soil hydration by reducing water runoff but keeps erosion at bay by softening the rain impact.

However, mulch decomposes and must be cleared from the bed when it is due. So, you must maintain a raised garden bed by clearing decomposed mulch, and you need to prune foliage.

It is also crucial to check the irrigation system, weed the bed, and remove weak plants regularly.

Prune according to the crop’s needs, design, and use. Also, add more mulch when you remove decomposed ones.

The mulch you use will depend on the region but ensure it is not less than two inches on the garden bed. In addition, monitor the plants for pests.

One option for pest management is using pesticides, but you can opt for natural control methods.

Use quality plants for your region and carefully handle the plants before and during the planting period.

How-to-Maintain-a-Raised-Garden-Bed

Conclusion

The depth of a raised garden bed depends on several factors. However, the standard depth is 11 inches. The crop of choice will determine whether or not you should go deeper.

Remember that the soil depth is not the only crucial factor when constructing the bed; height plays a vital role.

If the bed is deep due to the crop, the bed may become heavy and affect the construction. It also affects how well the bed drains.

It may be easier to use professional services to build a raised garden bed, but you can also follow this guide for a DIY project.

In addition, keep the garden bed well maintained. Ensure you correctly drain it, prune the leaves, use the correct type of mulch, and control pest invasion.

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