It was the first time I was growing a plant in a large planter. After buying a bag of potting soil, I realized I would need a ton of it to fill such a large container. But thanks to the advice of experienced gardeners, I found that I could use a filler instead.

To fill the bottom of a large planter you can use plastic materials like milk jugs, water bottles, or grocery store bags. You can use reusable materials like styrofoam or packing peanuts. You can even use biodegradable material like wood chips, leaves, newspaper, and cardboard.

As you can see there are a lot of options on what you can use as a filler at the bottom of a large planter. I’ll help you understand more about the materials so you can make your own decision on what works best for you.

Plastic materials

The benefit of using plastic materials is you may already have them or get them for cheap. The material is lightweight and will make it easier to move your planter around.

You need to be careful that the plastic is not toxic because the chemicals can harm the plant. This is very important if you’re growing edible plants in the planter.

Here are some of the plastic materials you can use as a filler.

  • Milk jugs
  • Water/soda bottles
  • Grocery store bags
  • Unused plastic pots

Reusable materials

Another good option that is cheap and you may have lying around the house is a reusable material. You may have got some packing peanuts as part of your Amazon package. Or some clay balls left over from your hydroponic setup.

Make sure that the reusable materials like styrofoam or packing peanuts are not made of a material that absorbs water. This will cause excess moisture in the planter and can lead to root rot.

Here are some of the reusable materials you can use as a filler.

  • Styrofoam
  • Soda cans
  • Clay balls
  • Packing peanuts
  • Floral foam

Biodegradable materials

You can use biodegradable materials as a filler in your planter. Just remember that such material will decompose over time. This could lead to compaction of the material and problems in the drainage.

You can use such material if you’re growing an annual plant that needs to be replaced after a year. Then you can remove the material and add it to your compost pile. And fill the large planter with a fresh supply of the filler.

Here are some of the biodegradable materials you can use as a filler.

  • Wood chips
  • Pinecones
  • Leaves
  • Sticks
  • Cardboard
  • Newspaper
  • Wood logs
  • Sphagnum moss
  • Coconut fiber

Heavy materials

If your large planter is going to be at a fixed spot outdoors, you don’t want people or vehicles knocking them down. That’s when using heavy materials as a filler in the planter can help.

The heavy material is also very sturdy and will last for a very long time without the need for a replacement. Just make sure the planter has good drainage after adding such materials otherwise you can face the problem of root rot.

Here’s a list of some heavy materials you can use as a filler in your planter.

  • Broken pieces of ceramic
  • Bricks
  • Cinderblock
  • Large rocks
  • Sand

What kind of material is good as a filler?

You know the type of material you can use for your filler. This could be plastic, reusable material, organic material, or heavy material. The type you should pick depends on your needs. And there are certain criteria that can help you decide what material works well as a filler.

Cheap

One of the biggest benefits of using filler material in a large planter is the cost it saves. If you use potting soil to fill the entire large planter, you will have to spend a lot of money.

But since you will fill 1/4th or 1/3rd of the planter with an inexpensive filler material, you can save up on the cost.

Lightweight/heavy

You can choose a filler material that is lightweight or heavy depending on your needs. You may need to more the large planter to collect sunlight or protect it from the rain, wind, or cold weather.

In such a case, it’s best that you pick a filler material that is lightweight. This will reduce the overall weight of the planter and make it easy to move around.

If you want to place the planter outdoors in a location that is visited by people or vehicles, you want to use heavy material as the filler. This helps prevent the planter from falling over in case a person or car accidentally pushes it.

Good drainage

You need to make sure the filler material you use has good drainage. Some of the materials can obstruct the flow of water from the soil and cause it to pool inside the planter. This can lead to root rot and damage your plant.

If you’re using material like rocks make sure to add a layer of landscape fabric between the soil and the filler. This will prevent the soil from blocking the gaps in the rocks and causing poor drainage.

Does not get wet

You want to use filler material that does not get wet and soggy when you water the planter. This can happen with materials like styrofoam or packing peanuts that are not waterproof.

This will cause the plant’s roots to soak in the excess moisture for a long time and causes root rot that can kill your plant.

Does not stick to the plants or soil

You want to avoid materials that would stick to the plant’s roots or the soil. This will cause a cut in the supply of nutrients, moisture, and air to the roots and damage your plants.

Does not leach chemicals

If you’re using materials like plastic bottles or metal cans, you need to be careful they don’t contain toxic materials like chemicals or heavy metals. These can leach into the soil and the plants.

If you’re growing edible plants in the large planter, this can be a cause for concern as it impacts your health. Make sure to pick a material that has been declared free of such chemicals.

How to fill a large planter with the filler

Once you have selected the filler material for your large planter, you can start to prepare it for your plant.

The first thing to do is to determine a place where you want to keep the planter. Once you add the filler and potting soil, the planter may become too heavy to move around.

You need to make sure your planter has sufficient drainage holes at the bottom. For a large planter, there should be at least 6-8 drainage holes. This will allow the excess water to drain out and prevent the problem of overwatering your plant.

If there are no drainage holes, you’ll need to use a power drill and make some yourself. Also, ensure the base of the planter can be kept at a little height so the drainage holes do not get blocked by the ground.

You need to then fill 1/4th or 1/3rd of the bottom of the planter with the filler material you have selected. If you’re using small plastic pots as the filler make sure to invert them with the mouth touching the bottom.

If you’re using materials like rocks, sand, or pieces of ceramic make sure to place a layer of landscape fabric on top of the filler material. This will keep a barrier between the potting soil and filler. And it will prevent the potting soil from falling out through the cracks.

Once you have filled the large planter with the filler, it’s time to add the potting soil. Keep adding the potting soil and press it gently so it falls into place. Keep doing this till there are about 2 inches remaining from the top of the planter.

You want to keep this space empty so that when you water the planter, it does not flow out from the top along with the potting soil. This will help you water the potting soil deeply as the water slowly gets absorbed in the potting soil.

Why you need to fill the bottom of a planter with filler?

There are certain benefits you get when you use a filler instead of adding just potting soil to a large planter.

Cost

The biggest benefit of using a filler is that it will save you a lot of money. Potting soil is expensive and if you have a large planter you’ll need a lot of potting soil.

You can get a filler material for quite cheap. You may even be able to reuse available material like packing peanuts, water bottles, or soda cans.

Weight

If you use potting soil to fill the large planter, it can get quite heavy and you won’t be able to easily move it around. This could also be a problem if you plan to keep it in an apartment or balcony.

The weight of the planter may compromise the structural integrity of the balcony. It’s much better to use lightweight filler in the large planter that will reduce the overall weight.

Soil compaction

If you have a large planter filled with potting soil and keep watering it after some time the soil will get compacted due to the weight. This means the soil will not drain water well. It won’t be able to provide the nutrients, moisture, and air to the plant’s roots.

If you use filler material in the planter, this problem of soil compaction can be avoided. The soil will drain the excess water through the filler material and out the drainage holes at the bottom.