"The Myth of Drainage Material in Container Plantings"

[Alison_Kristina]

This is interesting:

This is just one of those myths that refuses to die, regardless of solid scientific evidence to the contrary! Nearly every book or web site on container gardening recommends placing coarse material at the bottom of containers for drainage. The materials most often recommended for this practice are sand, gravel, pebbles, and pot shards. Other ‘benefits’ often mentioned include preventing creatures from entering through the drain holes, and stabilizing the container.

Nearly 100 years ago, soil scientists demonstrated that water does not move easily from layers of finer textured materials to layers of more coarse textured. Since then, similar studies have produced the same results. Additionally, one study found that more moisture was retained in the soil underlain by gravel than that underlain by sand. Therefore, the coarser the underlying material, the more difficult it is for water to move across the interface. Imagine what happens in a container lined with pot shards!

http://www.puyallup.wsu.edu/~Linda%2...20drainage.pdf

I have to admit, On occasions when I've transplanted plants from big pots, the soil above the gravel layer is always very wet.

So what is best to use for drainage, especially as I'm wanting something that drains well?

Looking on the web I see that some people are using hay or wood chippings underneath the soil. Do these really work?

Ali.

[Alison_Kristina]

Well, my first batch of spring onions failed. I'd planted them in a long container, gravel at the bottom (lots of holes in the container) topped off with growbag compost. I've just dug the compost out and, yep, above the gravel it's just a sodden mess of compost.

Ok, maybe I shouldn't have used growbag stuff, but still, despite all the holes and gravel, total lack of proper drainage . . .

Ali

[Ever Green]

Just a thought, I use the expanded clay balls at the botton of containers. The moisture travels through them and they act like a wick to draw off the water when the soil is wet. They also work the other way when the soil is dry if you water from the bottom. It works for me.. They work well in self watering systems as well.

[Alison_Kristina]

Clay balls, I've looked that up, appears to be an excellent idea, I'll try it out, many thanks

Ali

[Ever Green]

Hydroleca I think it's called. Shop around you can get it quite cheap.

[Alison_Kristina]

Shop around you can get it quite cheap

Yep, 99p for 50 litres I'll tell you how it goes . . .

[Ever Green]

WOWEEE I paid about 15 quid for 50 litres. WHERE, do tell I use it for everything.
Also (I haven't tried this yet, still reading up on it) I have read some stuff about good bacteria in soil. If you use hydroleca in your garden beds mixed in with the soil it acts to increase the surface area available for the good bacteria to grow on. Plus holding in extra oxygen and nutrients. I'm still looking into this so will let you know..