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Try Adding Container Fillers to Lightweight Potted Plants

By Jeff Rugg

Q: I have purchased several large lightweight pots in which to grow some veggies, etc. If I fill them all with potting soil, it is expensive and becomes too heavy to move. What can I use as a natural filler so the entire pot does not need to be soil?
Answer: There are several ways you can help this situation. Garden soil and potting soil are both too heavy for large pots. Potting soil often has a mineral soil base with lightweight additives, like perlite or Styrofoam beads, to fill some of the space. That’s OK, but it is still too heavy for a large pot.
Container soils need to be able to have lots of pore space — excess water drains out, but the soil still holds some water. The large pores that provide water drainage also allow air into the soil for healthy roots.
Actually, what we are looking for is a soilless mix. There are many recipes for making your own mixes or they are available at garden centers. They typically start with peat or coir fibers, which is ground-up coconut hulls. Then perlite, vermiculite, tree bark, sand, compost and other ingredients are added. For many plants, fertilizer and moisture-holding granules are added. For orchids, more bark is added, while more sand and less peat are used for cacti.
Soilless media tends to be pretty sterile without weed seeds, insects or diseases. Compared to garden soil, they are very light. They help to develop plants for several months, but they need to be replenished at least yearly as the ingredients decompose. Soilless media was developed by growers that ship their plants. They don’t expect the plants to remain in the pots forever and being lightweight makes them much cheaper to ship.
If the plants in your pots are annuals and will be replaced each year, you can knock the mix out of the pot each spring. Chop it up with the remaining roots and stir in one-third new mix. You can also add a few spoonfuls of fertilizer if necessary. If they are cheaper, you can also mix in bagged topsoil or potting soil, but keep them under a quarter of the mix. If you have too much, you can spread it into the garden, compost pile, flowerbed or on the lawn.
Don’t fill the media to the top of the pot. Leave it at least an inch or two lower. Then when you water, a good dose can be added without overflowing.
Two- to 3-foot tall potted plants need at least 6 inches of soil, while larger specimens need 8 inches or more. If the pots are taller than this (taking into account the watering space), then the bottom of the pot can be filled with lightweight fillers or left empty to save weight and cost. Be careful to consider that a top-heavy pot with a leafy plant may blow over. Pots that become narrower at the bottom are more prone to this compared to cylinder-shaped pots.
I have used plastic milk jugs, a big wad of plastic grocery bags, packing peanuts and cans as the filler. You want a filler that won’t decay, such as wadded-up newspaper or biodegradable packing peanuts. They will allow the plant to sink during the summer.
I prefer to place a cloth between the filler and the soil to keep the soil from settling into the gaps. Any cloth will do, but landscape weed barrier cloth is not going to deteriorate.
A product that works as the barrier and eliminates the need for filler materials is an “Ups-A-Daisy” planter insert. It comes in various diameters and drops right into the pot. It is reusable, and I love the ones I have. They have small holes for drainage and large ones in order to lift them out of the pot with your finger.
The large holes allow plastic tubing to run from a water garden pump under the insert to a fountainhead above the insert. Aquatic plant pots can sit on the insert at the right height, with plenty of open water under the insert for the pump. They are perfect for this use and for reducing the soil quantities in regular planters. Many garden centers are stocking this new product.
Another couple of ideas would be to place the pots on the patio first and then fill them, so they don’t have to be moved. Small plant dollies, which have wheels designed for being outdoors in the weather, allow the pots to be rotated and moved as necessary.
E-mail questions to Jeff Rugg, University of Illinois Extension at To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at

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