How To Fill A Wooden Planter Box

By   | Last Updated :   October 7, 2021 | Filed In :   Garden Accessory Ideas

We all know how stunning planter boxes look on a patio or deck or even around your garden. Unfortunately, filling these boxes in a way that keeps your plants healthy can be quite a challenge, not to mention expensive.

In this article, we will discuss the best and most cost-effective way to fill a wooden planter box so you don’t need to go through trial and error. Let’s take a look.

How to fill a planter box

Filling a planter box starts with preparing the box. If you’re using plastic planter boxes, you can jump straight to the filling section, if not, keep reading.

Preparing wooden planter boxes

Wood is a popular material for building planter boxes. Not only does it look great, but it’s also quite cost-effective to buy. If you like, you can save even more money by building one yourself.

The drawback of wooden planters is that they need to be properly prepared if you want them to last. This means lining the planter box with plastic as well as applying wood preservatives to prevent the wood from rotting prematurely.

If you can, choose a wood such as cedar that is naturally rot-resistant if you want your planter to last a few years, see our guide to building a cedar planter box for more tips.

There are quite a few types of planter box liners to choose from. The best bet is to go with one that is fully waterproof. A plastic liner will prevent the wood from being in contact with the moist soil all the time and slow down the rotting process.

Plastic liners can be secured to the box by stapling them with a carpenter stapler or by using wood glue to keep them in place. Make sure to create holes over the drainage holes in the box to allow water to drain as it should. If done correctly, the liners shouldn’t be visible after your box is filled.

What to put at the bottom of large wooden planters

Filling large planter boxes can be quite expensive, especially if you want to fill the whole thing with potting soil. If you want to cut down on some costs and improve drainage, consider filling the bottom of your box with the following materials:

Broken glass bottles

Broken glass is excellent for keeping the drainage holes of your planter open. It will also fill up some of the dead space in your planter. This means that you will need less soil to fill up your planter and you’re recycling old broken glass bottles at the same time.

Just make sure to be very careful when working with the glass to avoid cutting yourself. Also, take care not to cut yourself while planting. The glass needs to be buried deep enough to not be a risk or covered with wire mesh to avoid the danger. Wire mesh will also prevent the soil from falling in between the glass pieces which makes the whole process more cost-effective.

Styrofoam peanuts

How To Fill A Wooden Planter Box 1

Credit: Shutterstock

If you can find good-sized styrofoam peanuts, then you have an easy, lightweight solution for getting rid of dead space. Before you place the peanuts in the bottom of your pot, make sure to test them in water. Some types of styrofoam dissolve or shrink in water, you will need to avoid those.

If the styrofoam peanuts are too small and easily fit through the drainage holes in your pot, you can add coffee filters or a wire mesh over the holes to stop them from escaping without preventing drainage. You will also need to put some mesh over the styrofoam before you add your soil to prevent them from getting mixed up.

Broken ceramic

The next time a ceramic plate or cup gets dropped or a poor ornament is in the wrong place at the wrong time, don’t immediately throw the broken pieces away. You can use them to cover the drainage holes in your planters to prevent soil from falling out and fill up some of the dead space in large planters.

Gravel

Gravel is excellent if you need to add some weight to your planters while still maintaining good drainage. The gravel will fill up the dead space and make your planter a bit more wind resistant due to its weight. Just make sure to cover the drainage holes with coffee filters or something similar to prevent the gravel from falling out of the bottom of your planter whenever it is moved.

Small rocks

Small rocks are another genius way to improve drainage while adding weight to your planters. Small stones can be used to cover the drainage holes to prevent anything from falling out of your planters. You can also layer them in such a way that they improve drainage while filling up any dead space in large planters.

Wood chips

Wood chips are good for annual planters. Wood chips improve drainage but will also start to rot due to the anaerobic environment along with being constantly moist. As the wood rots away, it will compact and eventually stop proper drainage from taking place.

If you’re making a planter with annuals, you can use as many wood chips as you like since your pot will need redoing anyway within a years time.

How To Fill A Wooden Planter Box 2

Image credit: @emmet_van_driesche

Old containers

If you have some old containers and planters, it is always an option to see if they fit into your wooden planter. Fitting a plastic container inside your wooden planter will ensure that your wooden planter lasts longer. Just make sure to properly fill up your plastic containers and that there are drainage holes in them.

Tiles

If you’re renovating, do yourself a favour and keep some broken tiles. Tiles are great for closing up drainage holes in planters without preventing the water from passing through. You can also use them to fill up dead space in your planters as necessary by placing them in layers.

Keep in mind that large planters can become quite heavy. If you need to move your planter around quite a bit, make sure to fill it with something light like styrofoam peanuts. You can also use any of the above-mentioned materials to fill smaller planters.

Adding the top layer

Once you’ve decided what to use to fill the bottom of your planter, you will need to decide how much space you want that layer to take up. Usually, it doesn’t have to be a lot, 1/3rd is enough. After you’ve arranged the bottom layer, it is time to add the soil.

The top layer will consist of the potting soil of your choice. The kind of soil you choose will depend on what kind of plants you plan on adding to your planter.

woman holding potting soil over a hanging basket

Credit: Shutterstock

If you’re planning on growing succulents, you will need soil with a high sand content for maximal drainage. If you’d rather plant some flowering annuals, then a general potting soil will work just fine. In most cases, general potting soil will be your best friend.

If you’re growing plants that prefer acidic soil, then a high humus content is preferable. You can mix compost into the top layer of soil to help feed your plants and keep them healthy.

Make sure there is a layer between the materials at the bottom of your planter and the topsoil layer. The middle layer can consist of newspaper, cheesecloth or wire mesh. The only function of this layer is to prevent too much topsoil from falling into the holes left by the material at the bottom of your wooden planter box.

Don’t use any dirt from your garden to fill up your wooden planter. Plants tend to grow much better in commercial potting soil. You can, however, make your own potting soil by mixing equal amounts of perlite or vermiculite, peat moss and compost.

Adding plants

When adding plants, make sure not to remove them from their original soil. It is better to transfer them with the soil they are growing in. Dig a hole big enough in your planter to accommodate the plant and soil. Place the plant into the hole and fill up any remaining space around it.

Make sure to thoroughly water the newly transferred plants to lessen some of the shock. Your plants will also need to be placed in semi-shade for a while until they recover.

More on this: 10 of the Best Herbs to Grow in a Planter Box

FAQs

Do I need to fill the bottom of my planter with filter materials?

Preferably yes. Filling the bottom of the pot with a material that allows easy drainage prevents plant diseases such as root rot from developing.

What do I line planters with?

Planters can be lined with a variety of materials of which plastic is the most popular. It will keep moisture in and prevent your planters from rotting just a little longer. It will also benefit your plants since they won’t dry out as quickly.

How long do wooden planters last?

Most wooden planters will last between 5 to 15 years depending on where they are located and how they were prepared beforehand. Planters made from cedar will last longer than most due to being naturally rot-resistant.

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