How Deep Should a Planter Box Be?

Sage green EarthBox Root & Veg container gardening system

Planter boxes are a great way to grow vegetables and produce in a small space. You can place them on balconies, patios, or even indoors. They come in a variety of sizes and materials.

However, the biggest concern is depth. You need to ensure your planting box is deep enough to handle the root system for your plants.

Why is Depth Important for Gardening Containers?

Very simply, it determines how much room the roots of your plants will have to grow. Some types of plants, such as lettuce and herbs, have shallow roots. So, they can thrive in a gardening container that's only 6 inches deep.

Other plants like tomatoes, carrots, and potatoes require more rooting depth. They need a planting box that's at least 12 inches deep.

If you give vegetable plants too little space to grow, it cramps the roots. And that stunts their growth. It may even kill the plant. But one thing is sure -- your yields will fall well short of your goal.

Best Planting Box Depths for Different Vegetables

The good news is that you can grow various plants in indoor and outdoor planters.

Here is a general guide for how deep a planting box should be. It's also essential that your planting box has holes in the bottom for drainage.

The only exception is sub-irrigated planters (SIP) like those from EarthBox (they get great reviews). They include a reservoir at the bottom to provide a steady moisture supply to plants through capillary action.

Shallow Root Vegetables

Shallow-rooted vegetables should be at least six inches deep. They include lettuce, spinach, herbs, radishes, and green onions.

The EarthBox junior gardening container is perfect for shallow plant roots at more than seven inches.

Medium Root Vegetables

These vegetables (and fruits) include carrots, beets, broccoli, cauliflower, cabbage, peppers, and tomatoes. You'll need a planting box that's 12 inches deep.

EarthBox original planting boxes have been a staple for gardeners growing tomatoes and peppers. The company even offers a tomato-growing kit with everything you need for a big harvest.

Deep Root Vegetables

Potatoes, sweet potatoes, asparagus, melon, and squash feature deep roots. For example, potato roots extend at least 18 inches below the seed. That means you need a growing box that's at least that deep and preferably deeper.

Tips for Growing Vegetables in Gardening Containers

Now that you know how deep your planter box should be, here are other growing tips.

  1. Use a soil mixture that drains well and contains plenty of organic matter. Organic matter helps to improve drainage, aeration, and water retention. A good option includes a mix of potting soil, compost, and vermiculite. You can also purchase commercial planter box soils.
  2. Choose a sunny spot for your planting boxes. Most vegetables need at least six hours of sunlight per day.
  3. Water your plants regularly, especially during the hottest months.
  4. Fertilize your plants every few weeks with a balanced fertilizer like 7-7-7. You can use a water-soluble option and include it with your watering routine.
  5. Mulch your plants generously to help retain moisture and suppress weeds.
  6. Keep an eye out for pests and diseases. Act the minute you see any street signs.

Guarantee Your Success with EarthBox Gardening Containers

Planting boxes are a great way to grow vegetables and produce in a small space. By choosing the proper depth of the planter box and soil, you can enjoy a bountiful harvest from your container garden.

EarthBox planting boxes have been a hit with gardeners for over a quarter-century. They come with a 100% satisfaction guarantee. You can also get free shipping on orders over $149.

With EarthBox gardening containers, you can grow produce anywhere, even in the smallest spaces.