How Deep Should a Planter Box Be for Vegetables?

How Deep Should a Planter Box Be for Vegetables?

Planting vegetables in a planter box is an ideal way to grow some in your garden. This method saves you space and allows you to transplant the plants in the future. The main question is, how deep should a planter box for vegetables be?

The most widely used ranged depth in planting vegetables on a planter box is 6-18 inches deep. Plants like broccoli and cucumbers should be planted 6-8 inches depth, while radish, chives, and onions should be about 12 inches. Meanwhile, carrots, pepper, and tomatoes are ideal for planter boxes 18 inches deep.

In creating a planter box, the depth depends on the type of vegetables you want to plant. We advise you to learn the full growth potential of a vegetable before building your planter box. In this article, we will discuss the ideal depths for certain vegetables to be planted in a planter box and the things to consider when making a planter box.


How Deep Should a Planter Box Be for Vegetables?

The recommended depth for vegetable planter boxes ranges from 12-18 inches deep, although 6-8 inches is enough for some vegetables. Some plants require deeper depths as they grow huge over time. Roots should have enough room to develop and sufficient space for nutrients to get absorbed.

A planter box provides several advantages in planting different kinds of vegetables or flowers. For instance, they can help avoid pests, keep weeds away, and much more. Although a planter box seems like a good alternative to growing vegetables elsewhere than on the ground, you should know how deep it should be for different types of vegetables.

Before you decide to use a planter box to grow your vegetables, note that there is a recommended depth for certain vegetables. Some plants may need a shallow box, while others require a deep one. The following are the plants with their corresponding depths:

  • 6-8 inches: turnips, broccoli, cucumbers, and beets.
  • 10 inches: cabbage.
  • 12 inches: oregano, parsley, spinach, radish, chives, basil, coriander, corn, snow peas, shallots, beetroot, lettuce, Bok choy, and onions.
  • 18 inches:  carrots, peppers, and tomatoes.


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Significance of a Planter Box’s Depth

Every plant has its own characteristics and sizes. The depth of a planter box is dependent on the terms of the plant’s growth. It will give your plant space to reach its complete development.

Before planting a vegetable, look at its full-grown size and make it proportional to the depth of the planter box. Remember that if the roots of specific vegetables are too restricted to grow, it may result in a lack of fertility, root-bound, or deficiencies. Plants require several factors to develop successfully, and placing them in a compacted space may stop their proper growth.

Take care of your vegetables properly for them to be productive and healthy. You’ll know if a plant is less productive and lacks nitrogen if the leaves start to turn yellow. Nitrogen is one of the most needed elements for chlorophyll.


Root-bound Plants

Root-bound plants happen if a plant’s ability to grow is restricted. Plants’ roots are usually compacted in planter boxes or pots, hence why you should observe the importance of a planter box’s depth.

If a plant starts growing bigger than the planter box, the roots will find their way to grow. Pots bear a hole for drainage that will serve as a way to the developing roots. As for the planter box, the roots are limited to a secluded room, which affects their growth.

The roots of a plant will grow in circles inside the box, which will hamper them from absorbing the needed nutrients and water. The room for water will be small, which is insufficient compared to the required amount for the plant. This will result in chlorosis wherein the leaves turn yellow due to the lack of nutrients.


How much soil is needed for a planter box?

Leave a gap about 1-2 inches at the top of your planter box for vegetables. It will prevent you from washing away the soil when you water the plants. The soil you filled in the planter box will narrow down over time. After the growing period, the depth of the soil may sink to 1-2 inches.

It is highly recommended that you apply topdressing during fall and spring. Since the soil may shrink, you should top it up twice yearly. This method can help maintain the depth of soil for the development of plants and nutrients.


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Things to Consider When Building a Planter Box

You should first pay attention to the site where you want to situate your planter box. Create a drainage system and some irrigation to provide the plants with all the water they need to stay healthy. Amend the soil you will use for the successful development of the plants.

A planter box requires a specific size and height to prevent you from bending too much while gardening. Also, provide support inside the planter box to ensure that it won’t bend over time as you water the plants. It will play a crucial role in guaranteeing the longevity and efficiency of the box.

If you decide to plant vegetables in a planter box, we advise you to plan everything before engaging in all the work. Although the structure may seem easy to build, the whole process and product greatly affect the growth of the plant.

Pick the ideal site

Before proceeding to plant your vegetables, choose the most ideal site for them. Sites are where your plants stay and develop. Thus, they are a crucial factor that contributes to their overall growth. Several vegetables need sunlight; you should pay attention to them.

If a vegetable requires sunlight, pick a site that the sun directly hits. Avoid planting them in a place where the afternoon sun will strike them. Make sure the vegetables receive all the sunlight they need.

In terms of cool-season vegetables, like cabbage, broccoli, and many others, look for a site with shade. However, some cool vegetables may not tolerate shady areas. Thus, be attentive to their characteristics. For windy places, situate the plants somewhere where they are guarded against the winds. Although, make sure there is proper ventilation to prevent the development of diseases.

Create a drainage system

A planter box should possess a drainage system. Water in the soil can hamper the plants’ roots from absorbing oxygen. The wet condition of the soil is also a target for several diseases for plants. That is why you need to implement proper drainage in the planter box to drain the excess water from the soil.

Since your planter box is raised above the ground, water is fairly drained. This can only happen if you put holes at the bottom of the box, which prevents the water from fully soaking the soil.

Good drainage does not only drain the excess water but also prevents the walls of the planter box from absorbing it.

Soil amendments

Apply some soil amendments to your garden soil. This element can help improve the soil to support the plants’ development. Adding peat moss can also lighten the texture of the clay soil and enhance the texture of sandy types.

When adding peat moss, you should add lime to make the soil pH proportional. The purpose is to level the acid level of the peat. You can also put the rock phosphate recommended for acidic soils. After the application of soil amendments, you can proceed to add soil on top.

Apply the fertilizer and compost after you top up the bed. Note that you should add the last amendments at least a week after planting your vegetables to avoid the absorption of all the amendments into the soil.

Soil amendments serve as the helping hand of the soil in preparing and conditioning for planting purposes. There are two types of amendments, organic and inorganic. Organic amendments are made of dead, alive plants, or animals near to decomposing, while inorganic is manmade or came from mining.


While hand watering is a commonly used method to water plants, it requires a lot of work to put into place. You should also know how much water the plants need and when to water them. The idea of having an irrigation system is the best alternative when supplying vegetables with water in the raised beds.

Another way to water your plants is by using an automatic sprinkler system for plants. The only problem with this equipment is when the sprinkling process is scheduled, as it will work whether it is raining or not. It can greatly benefit you as the gardener but may also bring disaster to your plants.

The use of sprinklers may present disadvantages, but it is efficient if you set it properly. If you decide to use the sprinkler system, you can set it to pop-up or with the use of risers. In installing these sprinklers, you should consider the height, position, and extended position of the head compared to plants.

Sprinklers are recognized to minimally shower plants, but you can’t guarantee whether or not they receive the right amount of water for their development. For that, you need to set them at the right angle, so that the watering method is in proportion to all of the plants.


In building a planter box, what you need to take is limited to the plants and your own body. Indeed, if you have body mobility problems, making your box higher can solve the issue.

If your plant is lower, you will then force yourself to bend to garden. Before you start building your planter box, plan how to make it higher. There are specific common sizes when creating planter boxes, but you can customize your own if you want to.

Bed Support

After constructing a planter box, the next thing to do is support the inside of the box to its walls to prevent it from warping when used over time. This support is usually located in the middle portion of the planter box. The material acts as a brace of the whole box, giving durability to the hold if you fill it in with soil.

Watering your soil inside the planter box may affect the durability of the box as it is usually made of wood. As you water the plants, the wet soil can contribute to the absorption of the water to the box, which can warp the walls of the planter box. Some stores that sell this kind of support are made of wood, aluminum, and plastic composites.


Pests are always there, whether you plant your produce on ground soil or in a planter box. They will find a way in your box, and the worst thing to do is dig the box to offer them access to your plants. This circumstance usually happens if the planter box is bottomless.

The best way to prevent these pests from damaging your plants is to put a liner at the bottom to stop the pests from entering the box. You can use a hardware cloth to cover underneath the planter box. Other animals tend to enter your box from the top, which means you may also need to cover the plants at the top.



Using a planter box is another way to grow vegetables successfully. In this way, you can transfer your plants to other locations with relative ease. Some people may not know this method, which can benefit them in the space of their garden. With a little bit of creativity, you can make the most out of the space that you have with the help of planter boxes.

Building a planter box may seem simple, but there are factors that you need to consider to ensure the efficiency of this device. The depth of the planter box is a major factor affecting the growth of the plants. You need to observe the characteristics of the vegetables you want to plant to avoid mistakes in the development of their roots, which may result in the root-bounding of the plants. By doing this, you will be able to get a planter box that has the perfect dimensions that your plants need to grow and thrive.

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