What's Your Container (Potting) Mix?

Mix

You can either make a soil-less substrate, or a soil mix, but not a mixture of both. Although coir is good, roots do have trouble extracting moisture from it, and shredded peat moss is better for some applications. Traditional soil mixes will never be as good a soil free types, as the latter allows for better oxygenation, drainage, and retain their structure for much longer. The best piece of advice I could give you is: As the roots grow, so does the tree. The downside is soil free mixes are expensive are to set up. But yeah--the pros definitely outweigh the cons.

Adding manure to a soil free mix will ruin it for a variety of reasons as it will cause the mix to cloy, go foul, will cause perching in your pot, and will ruin its drainage properties over time. Horse manure can introduce root rotting fungi to your soil as well as other pathogens if it isn't cooked (composted) sufficiently.

What you need is a mix of either coir, pearlite, and vermiculite or swap out the coir for peat moss, and you need to fertilize with liquid hydroponic nutrients. You can get A & B mixes at very low costs prices which will last extremely long time--check out the bloom range. These are more complete than things like horse manure and are correctly balanced, and are a total nutrient and trace element feed. They will also come with dilution ratios which will make sense in a run to waste system, which is what your setup will be. You will get much, much, much better results doing this--and will preserve the life of your mix. You also don't ever want to mulch your pots with organic matter in a soil free mix.

Secondly, you will be better off with air pruning pots in the long run. I suggest looking into these. They do tend to dry out, and can blow over however. The best way I've found to counteract this is by mulching with pebbles/stones. They don't break down, add weight t0 the pot, retain heat over the day meaning more of it is delivered to the roots whilst reflecting harsh light, and allow liquid feeds to pass through completely. Another bonus is that they act to break the water flow caused by high pressure hosing--which is very bad for soil in pots as it ruins soil structure which is the main cause of perching, and can cause soil free mixes to separate meaning you get layers of pure coir and layers of pure pearlite/vermiculite in the pot, which isn't what you want. Mulch with stones at a depth of about an inch.

I now just use straight B&Q multipurpose compost, sometimes I add in a bit of heavy clay garden soil to help it stopping drying out.

The best mix I ever used though was Mels Mix from square foot gardening, it is 1/3 straight compost, 1/3 peat and 1/3 course Vermiculite, just too expensive to use though on everything.

Hi Starling,

Are you saying that a coir/well-rotted compost mix just wouldn't work? I have a friend who very successfully used a peat/composted manure mix for his outdoor containers, amended with fertilizer. My understanding was that coir can be successfully interchanged with peat.

I want to avoid going completely "hydro" if I can.

If you can make sufficient compost try this. Potting on smaller plants I part sifted compost I part sifted soil and one part sharp sand. I use different mixes for larger plants. Seems to work fine for me. I've given up on the terreau, compost, we get here it's rubbish.

Hey Maverick,

I imagine the vermiculite was the most expensive thing? Am I right in assuming he says that it lasts quite a while though? Sq. metre gardening is on my bookshelf waiting to be read

Hey Roitelet,

Unfortunately I don't have access to either soil or home-made compost ...sharp sand isn't problem though!

It will work, but won't have much longevity, and you run at a greater risk of bad things happening. It depends what the purpose is. For vegetables, it would be fine as you're always going to be changing the soil/turning it. For fruit trees it is far, far from ideal.

Coir can be interchanged with peat, but peat is still better. Also, if you by cheap coir it can contain salt which is bad news, and yes--it doesn't relinquish moisture easily. Water tends to cling to it better than roots can pull it out. This can be a good thing or a bad thing depending on the application.

A run to waste system isn't really a hydro setup, it's semi-hydro. It's basically the same as soil container growing, but is more efficient, less labor intensive, is less expensive over time, and well....better, if you want my honest opinion. You will never be able to replicate the yields achieved by this method with traditional kinds. Don't be frightened of the word hydroponic--organic growers tend to bastardize the term, but this isn't really founded on logic. Hydro nutrient runoff is not good for the environment, this is true--but neither are detergents, oils, and pretty much a myriad of things we leech into the natural world as a consequence of day to day existence. The only thing I have ever found not to grow better in soiless mixes are figs. They actually enjoy being potbound in crappy, low nutrient, compressed soil.

Don't get me wrong--if you want to use coir, use it. But you will need to add more pearlite if you do this, because, believe it or not, it transfers moisture to roots much better than the coir. You wouldn't think so, but there you go.

I am coming at this from the perspective of growing fruit trees. If the intent is to grow vegetables, you can disregard everything I've said entirely as I'm no expert of veggies by any means. But don't not go semi-hydro because of environmental concerns, most of the claims against it constitute absurdity, and all of them constitute hypocrisy.

yeah Vermiculite is expensive, lasts about 2-3 years, If you ever try it I would get the course stuff as that will last the longest and its what Mel recommends, its about £20 per 100l

Beautiful stuff though, was light and fluffy, didnt dry out or crust.

In the end though it was just too expensive, this year Id made up 8 new raised beds and I would have loved to have filled it with mels mix but that meant spending (from memory) £400 on mels mix or £100 on straight B&Q compost which has always served me well.

Hey Starling,

Thanks for the in-depth reply! I'm not actually that opposed to hydroponics...one of the things I want to start experimenting with is a proper hydro indoor set up when I get a little more space. I think the whole "it's not organic or natural" attitude is a bit silly...there's much worse things.

This is actually for seasonal outdoor vegetable growing, but I would like to include some perennials there too. That said, I would like to be able to "reuse" the mix rather than having to replace it every year.

I suppose my other question with the soilless mix - say I'm using a mix of coir, perlite and vermiculite with a regular balanced feed - is that it will be outdoors. Is the absence of any bacterial life not going to be a bad thing?

If you look at this compost (grochar), you'll see that it's mainly coir, vermicasts (so lots of bacterial life) and fertilizers: https://www.quickcrop.ie/blog/2013/0...ainer-growing/.

Am I wrong in assuming that compost (green and brown waste specifically) can be interchanged with well-rotted manure? The nutrient profiles are quite similar aren't they?

Just out of curiosity, if you were to recommend an ideal mix that isn't completely inert what would it be?

Sorry for the many questions!

Warmly,
Dan.

The B&Q compost has been my go to as well. It just annoys me that I don't know what's in it...wish they had the ingredients on the back...especially with the peat free which looks to have a lot of wood chips in it.

Shame you can't make the vermiculite yourself!

Ok, so the point of bacteria is that they break down organic matter into its essential properties which adds minerals and nutrients to the soil. The thing about hydro nutes is that they are those minerals, so really, bacteria isn't necessary because you're still getting the same thing--just in controlled, more complete, and measured portions. If you want to can add some Mycorrhizae spores to the soil free mixes, this is fine. It does boost root growth, I definitely notice the effect when I use it--which isn't often because it costs a small fortune.

That mix is just compost. Very expensive compost. Not only that, biochar is incredibly over-rated. I have experimented with it quite extensively and have cooked literally hundreds of liters of it, and my opinion, after those trials, is that is it effectively does very little, if anything at all, to improve soil quality and it is vastly inferior to pearlite. Do you know what the PH of char is? It's around 11. Super alkaline. Almost nothing in existence has that kind of preference.Compost isn't a true substrate, and it will break down quickly, which means you will have to keep topping up the pot/bed all the time. It also doesn't balance moisture well--it gets waterlogged. Sure--it will work , but it won't be as balanced. The smart play is to invest a little more money at the start--ultimately, you'll get more bang for your buck, and you'll be eliminating a lot of variables. Something else to consider is that if you do go the air pruning pot route, compost will be a very poor choice for these.

If you're going to go a soil based mix, you're better off avoiding this overpriced shenanigan and simply mixing your own. If it were me, I'd mix humus ( if you can get it) fine double washed river sand ( for structure, drainage) and any light, fluffy potting mix or soil you can find. And just use seasol treatments, which are a godsend and vital to growing anything well either in soil mixes or just in the ground generally.What are you growing? If it is things like lettuce, tomatoes, etc then you don't need something ultra sophisticated anyway--those are hardy crops. The only time you might need to replace the soil is if you're growing things like potatoes etc. Otherwise, you're really just looking at crop rotation. If you live in an area that gets a lot of rainfall, or if your sunlight is not especially harsh, you really don't need coir or peat at all because its main purpose is to retain soil moisture. Honestly I would go with something simple, and save your money for future infrastructure if you're just starting out. A lot of these expensive products are total overkill and really unnecessary.

I'd need to see what you're growing, and what your aspect is like to give you a more detailed response.

For what its worth, I grow quite a few sorts of veg in pots with the following regime:

Seeds grown in modules or small pots for transplanting - new MPC
Tomatoes, cucumbers, melons - new compost from tomato grow bags.
Brassicas - new MPC or recycled tomato compost with BFB added with a layer of new on top (never replanted into brassica compost)
Carrots - recycled brassica or tomato compost
Other crops (spinach, beetroot, courgettes etc) - recycled compost with BFB added and a layer of new on top
Potatoes - preferably fresh out of the hotbin with vermiculite added, or recycled with BFB and vermiculite

Often when recycling the compost I simply fork in some BFB and replant the container, but if not, I have a dedicated compost bin where used compost is tipped for later use. I might use this for refilling the pots, or for spreading on the veg garden as a mulch.

Sounds much more complicated than it actually is.

I keep it fairly simple, 2 parts multipurpose of whatever variety and considtancy and them 1 part manure. The compost forms the bulk and the manure the organics and other bits.

So far it has worked well, potato crop was good this year. From one container I have eaten 3 meals and have just dragged the rest out and have 3 or 4 more meals worth. They were Anya potato's.

Half the used compost has just been added to a couple of rows on the raised bed where needed and the rest just on the patch where the fruit bushes are.

For melons I found 1 part compost to 1 part manure was better, they seem greedier.

For pots, I fill the bottom layer with an inch or two of my garden soil which is predominantly clay. Clay isn't ideal for developing the roots of young plants I've found, but it helps trap nutrients and water, preventing a lot of it exiting through the holes in the bottom and evaporating away while allowing the longest roots to tap into this supply if needed.

Above that layer it will be a mix of slow release fertilizers (bonemeal and /or chicken pellets), horticultural grit for drainage and of course plenty of compost.

I leave a small area empty below to rim of the pot. When I've got some grass cuttings from the lawn I add this to the pots so it's nearly full to the rim, this helps to suppress weeds, aids moisture retention for soil, provides a slow release of nutrients to the soil. Then just repeat this step during the season as and when the pots need it.