I used fiberglass screening over the holes (to prevent the soil from washing out) and then put some old nylon stockings folded to briquet shape over each hole; my thought being that the screening might eventually get blocked but that the nylons should help hold the soil away from the screen. The barrels are five years old now and still seem to drain okay. The metal ring on one barrel has broken, so I'll probably transplant the contents (a spirea japonica) and then take it apart to see if any of the nylon remains. The next time, I will treat the barrel the same as a hanging pot, and line it with overnight diapers... after painting all the metalwork with a rust resistant paint.

Ditto the screen. You can use any window screening material, even copper to keep slugs or snails from using the moist holes as daytime hiding spots (not one store here carries the copper though). The perforated plastic landscape fabric also works to keep dirt in, let water out.

I've used squares of nylon stocking on smaller pots but haven't tried it with the larger, more permanently planted perennial containers.

If your holes are half an inch in diameter, chuck some 3/4 inch gravel in the bottom...you don't need much.

Screens work too, coffee filters might work, gutter covering wire screens...no end to what you can use.

I fill the bottom of large pots with over turned plastic flower pots and put styrofoam peanuts between. Than works for several years before I run into problems. And just filling the bottom with broken up styrofoam works too....you need to put soms sort of cloth over the plastic to keep some of the soil from filtering down, but it lightens the pot and keeps it from rotting for a few years longer.
Linda C

Neriad - Layering "stuff" in the bottom of your containers can make them lighter & can reduce the total volume of soil needed to fill the container, but it's ineffective at improving drainage. The practice simply raise the layer of saturated soil higher in the container. If it appears to work, it is by virtue of the fact that it reduces total soil volume and therefore the total amount of water the container will hold, which allows the plant and evaporation to reduce water in soil to a more favorable moisture level in a shorter time.

Using a uniform soil with good aeration and drainage from top to bottom in containers will provide an optimum root environment with no "perched" water suspended above the drainage layer. If you think that your planting is initially over-potted and the soil holds water too long, inserting a wick through the drain can be employed to drain excess moisture until the plant establishes.

Drain holes do not clog unless your soil has an inappropriate volume of fine particulates. Look to your soil structure for your answer, not the size of the holes or the type of material used to cover them.

You didn't say what you're growing in, but it's likely too heavy and contains too much fine material like sand, compost, or garden/topsoil - all aeration and drainage destroying ingredients.

Al

Great info everyone! I am growing in Miracle Grow Potting Mix. Al, any recommendations for good soil that would improve drainage?

I am very active on the container gardening forum & have many, many folks there, and most of my friends, growing in a basic mix that is easy to amend with additional ingredients or by adding additional volume(s) of the basic ingredients. It consists of:
5 parts pine bark (partially composted or aged is best, but raw will work if you're aware that you will need to add extra N)
1 part sphagnum peat
1-2 parts perlite (depends on where you live & what the bark structure is like)
garden lime
controlled release fertilizer
a micro-nutrient source (I use Schultz Micro-max and fish/seaweed emulsion)

Al

At the bottom of the first post in the thread I'm linking you to, find another link to the original post that maxed out at 150 replies during the discussion.

Here is a link that might be useful: Read about it here