Planter boxes are a great way to grow vegetables when you don’t have room for a traditional garden or are just looking for an alternative way to put your green thumb to use.
If you’re thinking about using a planter box to grow vegetables, one of the first things you have to determine is how deep the planter box should be.
Unfortunately, there’s no easy answer to that question. But there are a lot of things to consider when determining what is the best planter box for you.
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What is a Planter Box?
Generally, planter boxes sit above the ground and hold the soil so you can plant vegetables without having a traditional garden. They’re usually made of wood or durable plastic. Some sit on the ground while others look more like a table, with long, tall legs.
There is a wide range of sizes when it comes to planter boxes. Some are small enough to hang over a porch railing while others are large and meant to sit on the ground while others are small enough to keep on your porch.
Why Use a Planter Box?
One of the great things about planter boxes is that they provide good drainage for your plants. Planter boxes don’t hold onto water the same way a traditional garden does, and they warm up and dry out sooner when the weather improves, extending the growing season.
Setting up planter boxes is much easier than traditional gardening because you have complete control over the soil. Because planter boxes are self-contained, you don’t have to worry about what’s going on underground. You don’t have to worry as much about weeds, either.
The higher the planter box, the easier it will be to tend to. If you’re young and spry, that might not matter much to you. But, if you dread the thought of bending over to tend to your garden and the back pain you’ll experience after, getting a taller planter box is a good idea.
Taller planter boxes are also a great option for anyone with mobility issues. Some of them can easily be cared for by people in wheelchairs.
If you choose to use a very tall planter box, say, one that’s two feet tall or so, it’s very important to ensure that the top of the soil has all the nutrients and amendments the plants need to thrive.
Vegetables, Soil Depth, and Planter Boxes
Now that you’ve considered draining requirements and comfort, it’s time to think about what type of vegetables you want to grow. Every vegetable has its own root requirements, and it’s important to keep those in mind when choosing a planter box.
Most shallow root vegetables have roots that are between 12 and 18 inches deep. Shallow root vegetables include basil, bok choy, broccoli, cabbage, cauliflower, celery, collard greens, corn, endive, garlic, kale, leeks, onions, potatoes, radishes, and spinach.
Medium rooting plants have roots between 18 and 24 inches and will need more room to grow. They include beans, beets, chard, cucumbers, eggplant, peas, peppers, summer squash, and turnips.
There are deep rooting vegetables, too, that can root as deep as 36 inches. Obviously, these vegetables need a lot of soil, so you need an extremely tall planter box.
Deep rooting vegetables include artichokes, asparagus, parsnips, pumpkins, winter squash, sweet potatoes, and tomatoes.
Special Considerations with Taller Planter Boxes
If you choose a tall planter box, you will need to do a little bit of extra work to ensure your garden thrives and your planter box stays structurally sound.
For one thing, if you have a tall planter box and plan to grow taller vegetables, you’ll likely have to stake each plant or use a trellis.
Taller planter boxes also hold a lot of soil, which means they’re much heavier than smaller and shorter boxes. When you water them, they get even heavier, adding more and more pressure to the side of the planter box.
Too much pressure and the sides of the planter box may start to bow. That means you will have to add support to make sure the planter box maintains its shape and doesn’t collapse. If you’re buying a planter box, these supports are usually already in place. But this is something to consider if you’re building your own.
So, How Deep Should a Planter Box be?
To figure out how deep your planter box should be, the best thing to do is figure out what you want to plant. Do a little research and figure out how long the roots are to determine how deep your planter box needs to be.
There are many planter boxes available, ranging in height from less than 10 inches to as tall as 50 inches. So, there’s something for just about every type of vegetable.
If you’re planning to stick to broccoli, spinach, radishes, or celery, go with a planter box that’s at least 12 feet deep. Eighteen inches might be a little better.
For plants with medium roots, you need something with more room. A planter box between 18 and 24 inches deep is a good choice for things like peans, peppers, eggplants, and cucumbers.
Deep-rooted vegetables, like parsnips, pumpkins, and asparagus, need a planter box that can accommodate roots that are as long as 36 inches.
As mentioned, there are a lot of planter boxes out there. After you decide what type of vegetables you want to grow, think about the other details. Do you want a planter box with legs that’s easy to care for? Do you prefer wood? Metal? Plastic? Steel?
Then, find a planter box that’s deep enough to accommodate what you want to plant in a style you love and start gardening!