How to Fill a Large Planter With Less Soil?

If you have a large planter that you need to fill with soil, it can get expensive to buy enough soil to fill the entire planter. Thankfully, there are some clever tricks you can use to fill a large planter while using less soil. In this article, I’ll walk you through several methods on how to fill a large planter with less soil, along with the pros and cons of each method.

Why Fill a Planter With Less Soil?

Before jumping into the various techniques, let’s first go over why you may want to fill a large planter with less soil in the first place.

Here are some of the top reasons:

• Save money – Potting soil and other planting mixes can get pricey, especially for filling large planters. Using less soil is an easy way to spend less.
• Reduce weight – A giant planter filled entirely with soil can get incredibly heavy. By using less soil, you reduce the overall weight, making the planter easier to move.
• Improve drainage – Extra space in the bottom of the planter creates room for excess water to drain out, preventing soil from getting overly soggy.
• Allow deeper root growth – With empty space at the bottom, plant roots have more room to spread out and grow down deeper.
• Make planting easier – Less soil means less you have to dig and fill in when planting new plants.

As you can see, there are plenty of excellent reasons to avoid completely filling a large planter with soil or other planting medium. Now let’s look at some techniques for accomplishing this soil-saving goal.

Techniques for Filling a Planter With Less Soil

When it comes to filling a planter without using as much soil, there are a few different approaches you can take.

Here are some of the most effective options:

1. Fill the Bottom with Packaging Peanuts

One of the simplest ways to take up space at the bottom of a planter is by filling it with packing peanuts. Here’s how it works:

• Gather enough packing peanuts to fill roughly 1/3 to 1/2 of the planter. Make sure to use the biodegradable cornstarch-based peanuts.
• Place some landscape fabric or weed barrier cloth over the drainage holes at the bottom of the planter. This will help keep the peanuts from falling out.
• Pour in the peanuts, filling up the desired amount of space in the bottom of the planter.
• Top with your soil mixture until the planter is filled.

The lightweight peanuts take up space while still allowing for drainage. And since they’re biodegradable, they won’t cause any long-term issues in the soil. The downside is that packing peanuts tends to compress over time, so you may need to add more eventually.

2. Incorporate PVC Pipe, Bottles, or Other Fillers

For a more permanent space filler, you can use PVC pipes, empty plastic bottles, or other sturdy objects.

Here are some pointers:

• Make sure to use materials that won’t decompose or leach any chemicals into the soil. Good options are PVC, HDPE #2 plastic, or unused concrete blocks.
• Cut piping or bottles to fit the width of the planter. Arrange them in the bottom of the planter like a grid.
• Fill in around the grid with packing peanuts or pieces of polystyrene foam insulation for added support.
• Top with landscape fabric to prevent soil from falling through.
• Add soil mixture on top.

This creates empty air space below the soil level while keeping the soil in place. The grid formation helps hold everything in place while allowing water to trickle through. The downside is that it takes more effort to set up initially.

3. Create a Bottom Layer of Polystyrene Foam

For a lightweight but sturdy filler material, you can use rigid polystyrene foam insulation boards.

Here’s how:

• Take insulation panels and cut them to fit the bottom of your planter.
• Floating foam boards work well as they are lightweight and easy to cut. Extruded polystyrene rigid boards also work.
• Place the cut boards in the bottom of the planter like a puzzle, fitting them together to fill the space.
• Fill any gaps with additional foam pieces or packing peanuts.
• Top with landscape fabric to keep the soil from falling through.
• Add your planting mix on top.

The rigid foam boards create stable, long-lasting air space in the bottom of the planter. The foam insulates plant roots while propping up the soil above. Just be sure to thoroughly waterproof any foam before using.

4. Fill the Bottom Section with Gravel or Pebbles

An easy option is to fill the bottom portion of the planter with gravel, pebbles, or broken terracotta.

Here are some tips:

• Add a layer of gravel or pebbles approximately 3-12 inches thick, depending on planter size.
• Larger gravel over 1 inch allows more air circulation, while pebbles under 1 inch create more weight-supporting mass.
• Angular or irregular shaped fillers hold together better than rounded stones.
• Top with mesh or landscape fabric to keep soil and gravel layers separate.
• Finish filling with potting soil mixture.

The gravel provides excellent drainage and weight to anchor the soil. Small pebbles can compress over time, so use larger rocks or terra cotta pieces for best results. Just be sure to separate the layers to prevent soil from filtering down.

5. Incorporate Mulch, Wood Chips, or Compost

For a biodegradable and organic filler option, use materials like mulch, wood chips, straw, or compost.

Here’s how to do it:

• Coarser mulches like wood chips work better than finely shredded mulches or compost.
• Fill 1/3 to 1/2 of the planter depth with mulch or other organic materials.
• Top with a sheet of landscape fabric, burlap, or cardboard to keep organic and soil layers separate.
• Finish by adding potting soil mixture on top.

The organic filler provides aeration, drainage, and nutrients as it decomposes. Just be aware that the filler will break down over time, so you’ll need to periodically add more. Maintaining separation between layers keeps the soil from compacting.

6. Create Drainage Reservoirs with Landscape Fabric

For a lightweight option, you can create covered reservoirs using landscape fabric.

Here’s how:

• Cut or fold landscape fabric into chambers or pockets. Attach fabric together with staples, tape, or ties.
• Arrange chambers in the bottom of the planter and fill them with packing peanuts, gravel, or other fillers.
• Cover the tops of the chambers with more landscape fabric.
• Fill the remainder of the planter with soil mixture.

The fabric creates air chambers that take up space without adding weight. You can customize the size and shape of reservoirs as needed. However, the reservoirs are less stable than rigid options. Monitor soil settlement and refill chambers as needed.

Factors to Consider When Selecting a Fill Method

When deciding which of these space-filling methods to use for your planter, there are several factors to consider:

• Planter Size – Larger planters will require more filler and more rigid support. Smaller planters can get away with lightweight organic fillers more easily.
• Planting Mix – If using a heavy soil mix, opt for sturdier fillers like gravel or rigid foam. For lightweight potting mixes, organic fillers work well.
• Drainage Needs – Gravel or chambers provide maximum drainage. Foam and peanuts allow some drainage but less than rock fillers.
• Plant Types – For plants with deep roots, maximize soil depth and leave more room below for roots. Shallow-rooted plants need less soil depth.
• Planter Material – Flexible fabric planters require completely stable fillers like rigid foam or bottles. More rigid planters can handle compressible organic fillers.
• Watering Frequency – If you’ll be watering frequently, ensure good drainage with gravel or foam. Less frequent watering allows more leeway.

Consider all of these factors when selecting which approach will work best for your specific situation. Combining approaches is also an option for increased stability and drainage.

Tips for Success When Filling Planters

When filling your planter using any of these soil-saving techniques.

Follow these tips for the best results:

• Always start by covering planter drainage holes to keep fill material from falling out. Plastic sheeting, landscape fabric, duct tape, or corks work well.
• Arrange filler materials evenly across the bottom surface area. Avoid creating low spots that could cause the soil above to settle.
• Tamp down fillers like peanuts or mulch to minimize settling and compression.
• If using gravel or aggregate fillers, angle the planter slightly when filling to distribute stones evenly.
• Use larger gravel and rocks at the bottom, transition

In Conclusion

Filling large planters without using copious amounts of soil is very doable with the right materials and techniques. Space-filling fillers like gravel, rigid foam, and landscape fabric can dramatically reduce soil requirements. Just be sure to separate soil and filler layers properly for optimal drainage. Follow the tips provided to successfully reduce soil volume while still giving plants room for healthy roots. Let your creativity run wild when it comes to repurposing materials as planter fillers. With the proper filler and installation, you can save yourself soil, money, and back strain when filling large planters in the garden.

FAQs

Q: How much space can I save by using filler materials in planters?

A: In general, you can reduce the amount of soil needed by 1/3 to 1/2 by incorporating fillers in the bottom of the planter. For a 12-inch deep planter, that means using 4-6 inches of filler materials.

Q: Should I put anything at the bottom before adding the filler materials?

A: Yes, it’s advisable to cover the drainage holes with landscape fabric, plastic sheeting, or mesh before adding fillers. This prevents the materials from trickling out of the holes.

Q: What happens if I don’t separate my filler layer from the soil with landscape fabric?

A: Without a barrier, the soil will gradually filter down into the filler material below, compacting it and defeating the purpose of the fillers. Always separate layers.

Q: Can I use food scraps as filler in the bottom of planters?

A: It’s not recommended as food scraps will decompose and compact over time. Use wood chips, mulch, gravel, or other non-biodegradable fillers for best results.

Q: How often do I need to check or replace filler materials in planters?

A: Check at least annually for settling or decomposition. Replace organic fillers as needed, usually every 2-3 years. Inorganic fillers may last 5+ years if properly installed. Monitor soil moisture and plant health.