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You want to grow plants and buy a planter box. But you wonder?

How deep should the planter box be so your plants don’t have any growth problems?

A planter box needs to be deep enough so the plant’s roots have room to grow. Leafy vegetables can grow in a planter box 6-8 inches deep. Root vegetables need the planter box to be 8-14 inches deep. Fruiting vegetables can grow in a planter box 12-16 inches deep.

This is a reference you can use when selecting a planter box for your plants. But I’ll give you a detailed list of 100 types of plants and the planter box depth that each one would need.

Why planter box depth is important for plants?

Plant roots absorb nutrients and moisture from the soil so they can prepare food. When the plant grows in outdoor soil, it has plenty of space to spread out the roots deep into the ground. But in a planter box, the depth limits the roots growth.

If the planter box has the right depth, the plant roots will get the required nutrients and moisture. Otherwise, it will cause poor plant growth. And the plants may suffer other problems like pests and diseases.

The planter box depth will depend on the type of plant you’re growing. Some plants need more depth than others. Because some plant roots can grow deeper and spread wider than others.

Some leafy vegetables like lettuce and herbs like cilantro have shallow roots. While root vegetables like carrots and fruiting vegetables like tomatoes have deep roots.

If the planter depth is insufficient for fruiting plants that grow tall, such as peppers, eggplants, and okra, they may even topple over with the weight of the plant.

Can a planter box be too deep for plants?

You don’t want to overdo and make the planter box too deep for the plants, as this can cause some problems.

If the planter box is too deep, you’ll need a lot more potting soil, which will get expensive considering the cost of the soil.

If you try to grow a small plant in a deep planter box, the roots won’t be able to absorb all the moisture. This means the water will sit in the potting soil for longer and can attract fungal problems like root rot.

Pro tip: Make sure that the planter box has sufficient drainage holes at the bottom so that excess water can drain out. Also, use a liner at the bottom of the planter box to encourage good drainage.

If the planter box is deep, the plant may not get the required stable base with the surplus of potting soil. This soil is soft and has an airy texture compared to garden soil. So the plant could topple over because of its weight as the potting soil shifts underneath.

How deep should a planter box be for leafy vegetables?

Leafy vegetables and herbs typically need less soil depth compared to fruiting and root vegetables. These include vegetables such as spinach, lettuce, and kale. Herbs like cilantro, mint, and lavender also need less soil depth.

These vegetables and herbs would do just fine in a planter box with a depth between 6 to 12 inches. You could even grow different leafy vegetables in the same container.

Here is a list of some leafy vegetables and herbs and the planter box depth they would need.

PlantPlanter Box Depth (inches)
Arugula12
Bok Choy8
Cabbage12
Celery8
Chard6
Chicory18
Collards12
Kale12
Lettuce6
Mustard Greens6
Orach12
Sorrel8
Spinach6
Swiss Chard8
Cilantro8
Basil8
Lavender12
Rosemary12
Thyme6
Sage8
Mint12
Parsley8
Dill12
Fennel12
Chamomile8
Tarragon12
Oregano8
Marjoram6

How deep should a planter box be for root vegetables?

It’s obvious that many root vegetables would need a deep enough planter box so they can grow well.

Some of these root vegetables, like turnips or beets, may need less than others, but typically you want to grow these vegetables in a planter box that is 6 to 24 inches deep. I’ve also included tubers like potatoes and pods like garlic on this list.

You can grow different root vegetables in the same planter box if it’s large enough to give space for each of them.

Here is a list of some root vegetables and the planter box depth you should use.

PlantPlanter Box Depth (inches)
Beets8
Carrots12
Garlic8
Horseradish24
Jicama12
Leeks18
Onions10
Potatoes15
Radishes12
Rutabaga12
Scallions6
Sweet Potatoes18
Turnips8
Chives8
Lemongrass8

How deep should a container be for fruiting vegetables?

Most of the fruiting vegetables require deep potting soil to grow tall and healthy roots.

You’ll need a planter box with at least 8-12 inches depth for growing such vegetables as tomatoes, peppers, cucumbers, or eggplants. I’ve also added vegetables like asparagus and Brussels sprouts to this list.

You should not grow different fruiting vegetables together because they will compete for nutrients and moisture, affecting growth.

Here is a list of some fruiting vegetables you can grow and the planter box depth they need.

PlantPlanter Box Depth (inches)
Asparagus12
Beans8
Broccoli8
Brussels Sprouts12
Cauliflower8
Corn12
Cucumbers12
Eggplant12
Endive6
Kohlrabi16
Okra10
Peas8
Peppers10
Pumpkins20
Rhubarb20
Squash12
Tomatoes12
Zucchini12

How deep should a planter box be for houseplants?

The depth of the planter box for houseplants would depend on the type of houseplant you’re growing.

Most houseplants would grow well in any planter box with decent depth such as 8-12 inches. Use your judgment to figure out how deep the planter box should be. Small plants like succulents could do just fine in a planter box with less depth, such as 4-6 inches.

If you’re growing flowering plants, note that perennials will need a deeper planter box than annuals. That’s because their roots grow deep into the soil to survive for years, unlike annuals.

Here’s a list of some houseplants you may grow and the planter box depth you can use.

PlantPlanter Box Depth (inches)
Anthurium8
Croton12
Orchid6
Pothos10
Red Aglaonema6
Snake Plant10
Peace Lily10
Succulents4
ZZ Plant10
Ponytail Palm8
Chinese Evergreen8
Grape Ivy8
Philodendron12
English Ivy8
Spider Plant6
Hoya8
Rubber Tree10
Cast-Iron Plant8
Jade Plant12
Weeping Fig8
Asparagus Fern6
Chinese Money Plant6
Yucca10
Air Plant6
Aloe4
Dragon Tree12
Calathea10
Bromeliad6
Kalanchoe6
Crown Of Thorns8
Christmas Cactus6
Schefflera10

How deep should a planter box be for fruit plants?

There are some fruits that could be grown in a large enough planter box. These include strawberries, blueberries, and even figs.

But other fruit plants grow into large trees and even if you want to grow dwarf varieties, the planter box needs considerable depth.

You may need a planter box that is at least 8 to 48 inches deep to grow such fruiting plants or trees.

Here are some fruit plants and the planter box depth you need for growing them.

PlantPlanter Box Depth (inches)
Melons16
Strawberries8
Blueberries24
Pineapple24
Cantaloupe16
Watermelon20
Currants20
Gooseberries18

Here are some of my favorite container gardening tools

Thank you for reading this post. I hope it helps you with your gardening needs. I’ve listed some tools below that can help you with container gardening. These are affiliate links so I’ll earn a commission if you use them.

Gardening Gloves – I find the Pine Tree Tools Bamboo Gardening Gloves really good for both men and women. It’s made from bamboo so helps absorb perspiration. They are also comfortable and fit very well.

Containers – You know picking the right container is crucial for your container gardening. I’ve written a detailed post on the best containers you can choose from. If you’re happy with a plastic container, you can check out the Bloem Saturn Planter.

Watering Can – This is a must-have tool when you’re growing plants in pots or grow bags. It helps to water the potting soil without splashing on the foliage. The Kensington Watering Can is stylish, strong, and can provide precision when watering potted plants.

TrowelGarden Guru Trowel is my favorite because it’s durable and comfortable to use. My gardening friends really love having a trowel because they use it for digging soil, mixing fertilizer, moving seeds, leveling out the soil, mixing compost or mulch, and also dividing tubers

Bypass Pruner – I really like the Corona Bypass Pruner because it’s durable and gives a clean cut that helps plants recover faster. If you’re looking for something cheap, get the Fiskars Bypass Pruner that is really good as well.

To see an extensive list of the best container gardening tools gardeners recommend, check out this resource that I made for you.