Planter boxes are fun.
You can grow several plants in them especially vegetables when growing your own food.
But you may have bought some planter boxes or reusing boxes at home that don’t have drainage holes. You now wonder if you really need to drill some drainage holes in these boxes.
Planter boxes need drainage holes so that the excess water can drain out and prevent overwatering. The excess salt and minerals collected due to fertilizer or hard water can also leach out from the drainage holes. The planter box may start to rot due to the excess water at the bottom.
You can use planter boxes without drainage holes but you’ll need to be really careful of the amount of watering you provide. I would recommend using a planter box with drainage holes when you’re a beginner just starting to grow plants.
In this post, I’ll help you understand the problems when using a planter box without drainage holes. And how to use such a planter box if you have no choice. I’ll also give information on the size and quantity of drainage holes your planter box needs and how you can drill some yourself.
Let’s take a look.
What happens if you grow in a planter box without drainage holes?
The biggest risk you’ll face is overwatering because the excess water has no place to come out of the planter. Overwatering ican cause fungal problems such as root rot.
The roots will start turning black and emit a foul smell due to the rot. They won’t be able to supply nutrients and moisture to the plant. So the plant will eventually die as a result.
You may feel you are providing plenty of water to the plants but they would be dying due to a lack of water due to such overwatering problems.
The other problem you’ll face is a build up of salt and minerals in the potting soil. This will happen as you keep adding fertilizer and watering the potting soil. The salt and minerals can’t leave the potting soil due to a lack of drainage holes.
They will keep collecting until the potting soil becomes toxic for the plant due to the excess salt. The plants will lack the ability to absorb moisture and start dying as a result of the dehydration.
If you’re using a wooden planter box and there is a collection of water that does not drain out, the wood will start to rot.
How do you use a planter without drainage holes?
You can use a planter without drainage holes but you’ll need to be really precise with the amount of water you provide.
You’ll need to measure how much water the potting soil absorbs during the initial days of the watering. You want to keep an exact measurement of the water and only provide that amount.
You’ll need to adjust the measurements depending on the season because the potting soil may need a little more watering during hot weather than when it’s colder.
You could use a moisture meter that will show you the exact moisture levels in the potting soil so you can avoid the problem of overwatering.
Another option is to grow plants that are hardy and can survive with less water. You can then only water the potting soil occassionally without having to worry that your plants are lacking water. This will help you prevent overwatering the plants.
You’ll need to replace the potting soil at least every year because of the problem of salt and mineral build up that I mentioned earlier.
What size drainage holes in planter box?
I would suggest you use 1/4th inch holes when the planter box is about 12 inches in width. For any planter box larger than that, you can use 1/2 inch drainage holes.
How many drainage holes does a planter box need?
You’ll need 6-8 drainage holes in a planter that is 12 inches in size. For a smaller one, you can use 3-6 drainage holes and it should be fine.
You can space the drainage holes 1-2 inches apart depending on how large the planter box is.
If you have a 6-8 inches planter, then a space of at least 2 inches is to be kept between the drainage holes.
As the planter gets larger in size, you can increase the spacing to 4-6 inches, and that should work well for such planters.
Place one drainage hole at the center. And then you can place the remaining drainage holes closer to the edge.
It will also help if you are going to place rocks or broken pot pieces at the bottom of the planter. Since the drainage holes are spaced well apart, there are fewer chances of them getting blocked.
How to keep soil from washing out of the drainage holes?
One of the problems you may face with drainage holes is the soil leaches out when you water it. So you’ll need to use some methods to prevent this waste.
My suggestion is to cover up the drainage holes with some material that will help drain out excess water but prevent the soil from leaching out.
Some good material for this purpose are broken terracotta pieces, newspaper, dried leaves, and coco coir.
I would not suggest using stones or gravel because they will choke up the drainage holes and prevent water from draining out.
How to check the drainage holes are working well?
Once you have prepared the planter box with the drainage holes, layer of material, and potting soil, you need to check if it’s working well.
Water the potting soil until the water starts draining out from the holes. Make sure it is draining out well and does not choke up. But also check that the potting soil is not leaching out.
You should also check that the water is draining out from all of the drainage holes and not just one or two of them. Otherwise, you have an issue that some of the drainage holes are not functional.
If you find any such issue, you can remove the potting soil and material. And start over again ensuring the drainage holes don’t face any blockage.
What precautions to take before making drainage holes?
If the planter box you have does not contain drainage holes, you’ll need to drill them yourself or get the help of an expert.
The effort required to drill drainage holes would depend on the material that the planter box is made of. But you would typically need a power drill for the task.
Make sure you have eye and ear protection before using the drill. I would also suggest a face mask to protect yourself from the dust that will fly.
Make sure to keep some old rags or clothes so you can clean up the mess that will happen after the drilling activity.
Keep some material such as burlap, landscape fabric, or newspaper below the planter box to give it a stable base when drilling.
How to make drainage holes in a planter box?
Make drainage holes in a plastic planter box
Plastic is probably the most convenient material to make drainage holes. You can usually find plastic planter boxes at nurseries or garden stores that already have drainage holes. Or they come with markings at the places that can have drainage holes.
You just need to push down on those markings with a sharp object like a flat head screwdriver to bring out the drainage holes.
Mark the locations on the bottom where you want the drainage hole. You can use a pencil to mark this. You can drill holes through the planter box using a screwdriver heated up in a fire.
If you’re using a drill, put the planter box on a stable table so the bottom is facing up. You can use a tarp, plastic cover, or newspaper to collect the debris that fall.
Hold the drill straight above the marked spot and start drilling slowly. Hold the planter box with one arm so it doesn’t move. Keep pushing the drill until it digs a hole in the plastic.
You can stop and add a little water in between if you need to cool down the drill. This helps if the plastic is very thick. After drilling all the holes, you should clean them up to remove unwanted plastic debris.
Make drainage holes in a wooden planter box
Wood is another material you can easily drill into. You may already have drainage holes in wooden pots that you buy from a garden center.
You can drill drainage holes into the wood planter box using a power drill. You can mark the location of the drainage holes on the bottom of the planter using a pencil.
Place the planter box on a stable table so the bottom is facing up. Fallen wood debris is easier to clean up if you place a tarp, plastic sheet, newspaper, or something similar underneath it.
To start drilling, hold the drill straight above the marked spot. To prevent the planter box from moving, hold it in place with one hand. Start drillig the hole.
You can stop drilling for a moment and add some water. It’s useful if you have thicker wood. Once you’ve drilled the holes, you can clean them up.
Make drainage holes in a metal planter box
You don’t have the problem of a broken metal planter box during the drilling. It can be difficult to drill through metal sheets if they’re thick.
You can use a diamond drill bit to drill holes in a planter box made from metal. Use the drill slowly and carefully so you don’t damage anything.
Put the planter box on something stable so you can reach the bottom. Make sure there aren’t any flammable materials around as sparks may be created when drilling through metals. Hold the planter box steady with one hand as you drill holes in the bottom.
Start drilling at a 45-degree position. Start the drill slowly, and apply gentle pressure on it. This will help it bore through the material. When it starts to cut a small hole, move the drill bit so that it is straight over the planter box.
You should stop after a little bit has been drilled. Then pour some water onto the drill bit and hole so they can cool off. And then you can continue drilling. Keep drilling until there’s a complete hole.
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.
Trowel – Garden 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.
Kevin is the founder of Gardening Mentor, a website that aims to teach people to grow their own food in a limited space. As a self-taught gardener, Kevin has spent several years growing plants and creating gardening content on the website. He is certified in Home Horticulture and Organic Gardening by expert gardeners from Oregon State University.