Drainage in planters/pots.

Guys, depending on where you look there is a hell of a lot of conflicting info when it comes to your drainage in outside planters/pots.

Some swear by the usual crocs, polystyrene, pebbles, marbles, whatever, anything to keep the soil away from the actual drainage holes. And this does make absolute sense to me, it seems a no brainer.

Yet others say you should NEVER put anything at the bottom of any pots because of a phenomenon known as the "perched water table", which I had never heard of until my recent research.

The perched water table, apparently, is a sure fire way of causing root rot, the very thing we try to prevent.

On one video I watched, some guy said the best way of ensuring proper drainage, thus ruling out root rot, is to water accordingly, don't overwater!! Well how the hell can you ensure this with outside pots? Bring them in everytime it rains, it's ludicrous.

It seems to me that the key element is the soil mix. A mix that can get absolutely saturated during a torrential downpour, yet drain freely without waterlogging.

Would I be on the right track with NO crocs whatsoever, and a good compost with maybe sand and/or perlite mixed in to aid drainage during even the wettest spells?

 

I'd say it depends on the plants in the pots. For most, I put mesh over the holes just to prevent the compost from being flushed out. For succulents and citrus I put a layer of crocks. We're all going to have a challenge on our hands as peat is definitively phased out of compost mixes. It was the ultimate material. Most of the replacements dry out on top, giving the impression that watering is required, but the underneath is still sopping wet. Whatever you do, don't use sand in the mix! It's a complete fallacy that it helps drainage. Horticultural grit is better. Perlite and vermiculite do open up the structure but they also retain moisture.

 

And often perlite seems to come to the surface and blow away! I love horticultural grit - the really sharp washed granite stuff - but it means the pots are heavy and you can't tell so easily by lifting whether they need watering.

 

I do use sharp sand, (not building sand), mixed with compost, especially if its JI compost, but as has been said it depends what you are growing and how much root the plants have when potting up.

My best mix is one 50lt bag of multipurpose with one bag of sharp sand and a bag of JI no3.

I then add grit for plants that like better drainage and use it as it comes for bedding plants and most other stuff.

I never use crocks as they just take up pot space but do put a single large crock over the hole of clay pots.
You tend to get water logging if you over pot, and in plants that have only recently been planted.
Just raising the bottom of the pot off the ground does a lot to help drainage in wet weather.

 

Think what Pete says above just as important as whats in the pot.
It only needs to be 10mm or above.

Never had a problem with or without crocks, though in larger pots with tall plants we add some heavy gravel or stones in the bottom to stop them blowing over.
That why we try to buy pots with parallel sides rather than those that taper down to the base and can be quiet unstable.

 

A lot of plastic planters are actually sold without drainage holes, they do have markings though where to drill.

We always use two tier drainage pots (Aero Plas) brand for growing patio, shrub plants etc etc. This means the whole bottom of the pot is not flush with the ground allowing surplus water to drain more freely.

The large heavy duty tubs for trees for commercial growers are like the image below They have the drainage holes at the bottom plus the side towards the bottom of the tub, these come in sizes from 10l to 1500l plus. People only tend to put stones at the bottom to prevent them blowing over, especially if its going to be planted with taller plants.

 

I agree, often pots are made for appearance rather than practicality.
I also avoid pots wider at the bottom than the top as you can't get the root ball out when it comes to repotting.

 

I agree! Those clay traditional clay or plastic pot feet you can buy are one solution, but you need to place them just right or the pot wobbles.... Easier to use are the black rubber ones I discovered relatively recently. There are various kinds, mine are just little black discs which are more less invisible in use. Not expensive and solved the problem I had with some pittosporums in galvanised planters in the front garden, which were sitting on concrete but still getting waterlogged and sulking.

 

I do a similar thing with a layer of landscape fabric or fine mesh over the base to cover all the holes, then have a free draining mix that suits the plant that's going in it.
For clay or glazed pots that have a single central hole, I use a bit of broken pot [crock] over that.
I've never liked putting a layer of gravel or stones in the base of any pot.
Raising the pot off the ground is important, especially if it's sitting on a solid surface like paving.

 

Raising a large plastic pot on feet can cause the bottom to sog and finally crack with the weight of the compost and planting.

My large (50cm) containers have a layer of whatnots (bits of broken plastic, old broken cups, stones...) in the bottom to give some pockets for the water to drain into, and are placed on flat surface with grooves (patio paving) to allow the water to drain out. Without the rubbish layer the compost tends to compact towards the bottom.

Tall plants get heavy rubbish to balance the container, shallow rooted plants (herbs and annuals) get a thick layer in order not to waste compost.

Houseplants usually get a piece of root membrane/ mesh over the holes to prevent stuff being washed out and an inch of gravel, pebbles, crocks or whatever I have. The downside is that you can't see if the plant is pot bound as the roots can't push through the holes.

I tend to mix horticultural grit into any compost I'm using, the mixture feels good and is less likely to glue together like plain MPC can do.

 

I put a few stones in the bottom, i don't use gravel for drainage and i use a multi purpose compost, it now has less peat in it but still ok for large pots. I don't have any problems knowing when to water or not. But using it for indoor use it has a lot more of those tiny black flies.

 

@Logan...stick some matches, head side down, in the pots to repel sciarid flies. Or @CanadianLori came up with a good, biological control for them on another thread. I'll see if I can find it...

 

Thank you @noisette47 i'll do that.

 

There you go, @Logan...Mosquito Bits: Kills Mosquitoes & Fungus Gnats | Planet Natural
https://www.amazon.co.uk/Summit-res...72787684&sprefix=mosquito+bits,aps,112&sr=8-5 there are a couple of options.

 

Thank you @noisette47 i'll have a look.