British pot gardeners have long used a mixture something like 1/3 sand, 1/3 peat, and 1/3 loamy garden soil. Peat is coarser and more durable than compost. Because of that and the heaviness of your loam, I would try 1/2 sand, 1/4 soil, 1/4 organic matter, with more compost than manure.

I have no experience with coir blocks, but if you could beat it into small pieces and dust, it would be a durable peat-like material that you could substitute for some of the sand and some of the organic material in that mix. It would retain water/nutrients better than sand and maintain volume better than compost.

Don't over-fertilize the soil mix. 10% manure gives enough nutrients for months of growth. You can apply fish or blood at the surface later on as needed. None of your fertilizers contains potassium. You can get that from green garden waste or vegetable scraps that have not been leached by rain, also from vegetable cooking water.

I know someone who uses those coir bricks exclusively for rooting rose cuttings so I think it would be good in a mix. Break it up very fine and mix it in with the garden soil and add some of the other organics. You just want to end up with a mix that is light weight and drains very well.

I use coir in my potting mix. Its primary advantage over other organics is that it retains its fluffiness and doesn't break down over time. Kind of interchangeable with peat moss that way, but considered to be more environmentally friendly as it is a renewable resource not being depleted over time, as one occasionally hears about peat.

To use those coir blocks, just put them in a wheel barrel and get them wet, then fluff. One at a time, as one block makes a lot of material fluffed. Then into the mix it goes. Coir's other advantage is that it holds water really, really well. So not too much, lol, or your plants will drown.

All of your materials sound quite heavy. Are you able to get something light weight to add to your mix? I can't give you proportions to use with that assortment, as you seem to be lacking a light, well-draining element. I use a great deal of perlite or pumice or Turface, depending on what's around. Then I just mix things until I like what I have.

Kathy, thanks for the tip about breaking up the blocks. I had no idea it was so easy.

Lightness is desirable for convenience in moving pots, but it isn't otherwise necessary. River sand drains really well.

American commercial potting mixes use only lightweight materials in order to reduce shipping costs. Soil-based potting mixes are widely used elsewhere in the world.

A standard British recipe is called "John Innes" :
7 parts loam*
3 parts peat
2 parts sand

*This would be a good medium or light loam with substantial sand content to start with.

I'm just wondering where you live that doesn't offer bagged potting mixes?
Wow!

Well I am in Karachi, Pakistan.

I guess John Innes is the best given what I have. Maybe I can substitute peat with coco coir?

I use the coco-coir for my orchids and its very lightweight. Saw that it is also used as a soil amendment to make soil "light". Nursery men just use river sand and manure in their pots.

Perlite is available, but very expensive! Nothing else "light i can think of except good quality compost. I do make leaf compost at home (leaves, grass clippings, fruit peels etc). River sand drains very well indeed but it is very heavy.

I mean imagine, if I want to move a 10 gal clay container full of garden soil!!

I have grown roses in containers, third year now using the local sand/manure mix. But the soil has become heavy and moisture retentive leading to root rot (I posted about it last week-roses dying). So now I will get some roses this winter so want to give them better conditions!

Oh and before I forget, thank you for the helpful advice!! :)

H

Yes, Peat and Coir are basically equivalent as far as soil mixes go. That substitution is fine.

But you are going to have -- I guess -- to use a lot of sand, and that's going to make for one heavy pot. So be it.

I was thumbing through the magazine Fine Gardening yesterday in a store and saw an interesting tip a reader sent in about making pots lighter. He put a big dowel in the drainhole so it wouldn't be covered up, then sprayed a spray insulation that hardens but is lightweight. I have used something from Lowes called Great Stuff to fill in small holes in my chicken coop so snakes cant enter. Its light and very durable. But if you cant get bagged potting mix, you might not be able to get this. I also thought of something else - in some packaged products [I just put some in the burn pile is why I thought of it] there are Styrofoam like pieces to hold a product in place and protect it [like computer parts in boxes]. If you had access to any of that, you could chop it really fine to take the place of perlite. If you have access to the gravel put in fish tanks, perhaps that could lighten the soil a bit, or even river gravel, chicken grit, packing peanuts.......

The loam used in the John Innes recipe would be around 75% sand. It might be a good idea to check the sand content of the native soil via a soil jar test. Pulverize a dry soil sample and shake it in a jar for a LONG time with water and 1 TB table salt. The sand will settle out within a minute and form a pale layer in the bottom. The mixture of river sand and native soil should be 80% sand before the organic matter is added, or else it won't drain well. Then you can add organic matter to make up 20% to 40% of the final mix. This should be mostly coir with some manure/compost for nutrition.

I was reading that coir can be a good material to use because it lasts a long time and retains water but is more expensive than peat. Sand is wonderful but it makes the pots heavy. I put my heavy pots on a stand with wheels because I like using sand.

Heavy pots are easily moved with a dolly.

I've been scooping around on youtube. We have a lot of trees so a lot of leaves. I was thinking of starting a leaf mold pile. I read some people use it to substitute for peat. It would lighten the potting soil correct?

H

In the long run, leaf compost is not a light material. It shrinks away as bacteria consume it. If the potting mix is mostly compost, it becomes a very dense mucky material with poor drainage. The guru on the Container Growing Forum doesn't use compost at all in his more durable mixes. It isn't really a substitute for peat or coir unless you will be repotting once a year in all-new mix.

Of course, it's good as an additive to garden soil or as a mulch. If you mix leaf mold into the soil before it is thoroughly made (18-24 months), it will rob nitrogen, so extra N will be needed. Eventually almost the entire bulk of compost will be eaten up, but a small amount of humic acids will remain as a long-term soil conditioner.