Hi Jodik thanks for your reply.

I have read those threads by tapla a few months back and I will read through them again; they put forward a strong case for inorganic container gardening.

What I like about the gritty mix is that it's so light weight due to all those big particles giving space for air. But I'm trying to strike a balance: enough drainage and enough water holding capability. No hand watering, no frequent repotting.

I do understand that good drainage is a must in order to prevent root rot and provide gas exchange. The question I have though is can gritty mix be modified so that it is suitable for twice weekly waterings in typical Perth summer temperatures of 35 C (95 F)?

I'm after what's great for the the gardener and good (not to say best) for the plant. I wonder whether Peter's mix might not suite the needs of a lazy gardener better than Al's?

I live in Adelaide and have been using gritty mix for nearly 3 years. It has no problems with water retention. Last summer was hotter than average with two days at 45C. Usually I was watering twice a week , rarely three times.
I either use Turface in the mix ( buy from Melbourne) or the Aussie made Kleensorb diatomite.

I don't want to sound too negative but make the following comments-
"good quality potting mix" -This is a misnomer as most are junk especially for long term plantings. If you can get the March 2013 edition of Burkes Backyard magazine there is some interesting reading.
Kitty litters are a minefield. Suggest you do a small test run first.
Not sure of pool zeolite is suitable for plants. I use a dedicated horticultural grade of zeolite in my other mixes.
Bonsai shops and clubs are often a good source of materials

Hi Alan,
It's great to get a response from someone who gardens in a similar climate - sounds like you had to endure a scorching summer last year! To be honest I was sceptical that the gritty mix would be suitable for our climates but now I'm intrigued. What does your version of the gritty mix consist of exactly? How does the gritty mix compared to other medium's that you've used? How often do you fertilise? Is it possible to use a controlled release fertilizer or do all the granules fall to the bottom?

And you don't have to tell me about the quality of potting mixes; I've definitely been burned in the past. I already have some Debco Raised bed mix though which I've found to be of fair quality so I think I'll still mix up a batch of Peter's mix but I might experiment with the gritty mix down the track to see how they compare.

As for the Coles brand clumping kitty litter - that was recommended to me at a GardenWise seminar by the Beyond gardens experts (www.beyondgardens.com.au). It's the cheapest available but other types have finer particles which are considered faster acting. The Zeo-chlor is also 100% zeolite and recommended at numerous places around the net.

Here is a link that might be useful: Debco Raised Bed Mix

This post was edited by arcan on Tue, Aug 12, 14 at 7:45

Hi Arcan
The plants I grow tend to need good drainage so they really appreciate a durable open mix like gritty compared to the bagged mixes I used before. The roots look so much healthier.
I have used Osmocote controlled release with success and also liquid fertiliser at recommended doses.
One trick I have learnt for plants in full sun is to have them in white or pale coloured pots -- heaps cooler than black pots.
I just watched Peter Coppins videos from your link, I agree with most of what he says. However the "drainage layer" at the base of the pot is not good - read what Tapla has to say about them .

Yes, Alan - that's why I didn't include that part of the video in my original post. I've included a link to an article that makes just this point about crocking.

I wonder if having a small layer of expanded clay would also cause this problem?

On another note: where do you source all the ingredients for the gritty mix? When I looked some months ago I found every ingredient but never in quite the right sizes.

Here is a link that might be useful: Rocks in pots? What a crock!

Arcan I suggest you go to my profile page and send me an email. We can then have a more detailed discussion about sourcing ingredients in Australia.

The grittier mediums allow for more frequent watering... in other words, allow for a wider margin of error, considering that most potted plants in general are killed by a heavy hand when it comes to watering.

I always water "as needed", and never on a specific schedule. I check individual pots for moisture content, only adding moisture where it's needed. The reason I do this is because each individual plant will use moisture at a slightly different rate, the medium within the pots drying at different times. It depends on the type of plant, the size of the plant, size of the pot, location of the pot, etc...

In my estimation, the grittier mediums are not really tailored for convenience... they're tailored for the health of plants. I'm not sure I would want to compromise when it came to my plants.

Good luck, though... I hope you can find what you're trying to achieve.

I understand where you're coming from Jodik. You must get great results using your fine-grained approach but as you say I want to try something more laidback.

I use adjustable drip irrigation so I can adjust the amount of water each of my pots get - I do this seasonally and I don't water at all in winter unless there's been a long dry patch.

In another thead Al suggested increasing the water retention of gritty mix by using 4 diatomite, 3 bark, 2 grit.

Now I just bought a 100L bag of coarse perlite and I found where to get diatomite and small pine bark. As diatomite holds more water than turface and perlite holds more water than grit, I figure a strait 1:1:1 mix of diatomite, perlite and pine would probably hold enough water. If not I could maybe add more diatomite.

Arcan : I have been experimenting with various combinations of soils and I agree that a 1-1-1 soil mix of pine bark, diatomaceous earth (DE), and perlite will hold a significant amount of moisture. In my very unscientific testing I've also used a 1-1 mix of pine bark and DE. That mix holds a lot of moisture, which would be good for very hot and dry areas.

Hope that helps.

TYG

Interesting discussion.

I hope you will keep coming back here and not go offline for too much of the exchange, since discussion of moisture retention is very, very relevant to lots of us. I am in LA and it's a problem. We are having water restrictions too.

Well with my very limited experiment on this I will say that a mix of bark and either Turface or DE will hold a good amount of moisture. The more Turface/DE the greater moisture retention. I can say that my spruce tree seedlings growing in a bark/DE mix are doing very well this year however they use much less water than a tomato plant for example.

This does not mean that all types of plants will do well in this mix so I can't recommend it. As I mentioned before this is a very unscientific test on my part. If you are curious about trying a couple of plants in this mix feel free to experiment. It might help some plants in very hot and dry locations.

Thanks

TYG

Thanks TYG - theory is one thing but its good to know that its seems to be working in practise too.

@Needs2SeeGreen - I mixed up a large amount of Peter's Mix maybe 500-600L on the weekend. It was very hard work even with a cement mixer (the sand weighs a ton); would have been impossible without one. So far I've potted up a double-grafted Mini Royal-Royal Lee cherry tree, a maltese blood orange and a meyer lemon. The cherry and lemon trees were root bound and needed a fair amount of root pruning.

I'm going away on holidays for for the next three weeks but I'll let you know how they're doing when I get back.

I experimented with DE this year and find it to be an extremely useful amendment. It really holds the water, and the pore size is big enough plants can utilize the stored water pulling it out themselves. Unlike turface which pore size is so small the roots cannot access it.
DE pore size is .36 microns turface is .045. Less energy is needed to release water from DE. Pore size is 8 times larger in DE! Turface can hold 95% of it's weight in water. DE can hold 145%,
The numbers speak for themselves. Source of info is the Axis company.

Some interesting comments here. I have been growing trees in large pots for nearly 30 years and have tried all the different suggestions. My videos were produced to show what I'm doing now.

Please be wary of information saying putting rocks/gravel in the bottom causes drainage problems. Yes, using just standard putting mixes (which are only short-term growing mediums) over a layer of rock or gravel, you may well get a 'perched water table'. But even with these crappy growing mediums, you must ask yourself "if I have a perched water table could that mean I'm watering too much?" - you don't have to be an Einstein to work that out.

You DON"T need water to drain out of pots - if that's happening then it's a total waste of the world's most precious resource. You want to be able to give potted plants just the amount of water they need to reasonably perform/produce. Period.

This is one of the reasons I put a layer of expanded clay in between. My trees are performing well with just 10-15mm of water per week, and this is in the middle of rainless 35-40 degree C weather with hot dry winds thrown in!

Cheers, Peter Coppin

Here is a post from the Garden Professors thst shows whst happens when you have a layer of fine media over a layer of coarse media. Notice the water stops at the coarse layer and moves horizontally until the perched water table is created and then moves into the coarse material. If you put a coarse layer of gravel at the bottom of the pot amd you use a mix that can support a perched water table, the gravel layer will move the perched water table to a higher elevation in the pot than it would have been had the gravel not been there. Now if you have a study showing otherwise Peter, I would love to see it.
Container Planting: intuition vs reality

I'm not saying you don't get perched water tables when gravel is put underneath standard putting mixes (especially if there are insufficient drain holes or, worst still, none). I'm actually saying two different things:

1. We need to appraise the use of standard potting mixes as a long-term growing medium, because they aren't designed for it. That's why I've developed my own over three decades with the addition of both clay and zeolite being absolutely necessary to hold moisture.

2. Too much precious water is wasted on pot plants. As I said, my advanced trees do quite well on 10-15mm a week in a hot, windy area, where I know a lot of people who use 30-50mm! It's a matter of careful moisture monitoring, though that's often easier said than done. This is why I put a layer of expanded clay between the gravel and my soil mix - it absorbs excess moisture (when that occurs), and plant roots get down into that layer and can utilise it.

How do you deal with salt accumulation?

As in the link Nil used (good link - I 'borrowed' the picture), I think this is a case of someone's intuition telling them something that in reality doesn't happen.

Most of us are focused on making it EASY for others to consistently bring along healthy plant material because that is their focus. Once your priorities change and you're bound to those priorities, you self-limit your options. There is nothing wrong with focusing on saving water, but we all need to individually make the decision about the cost of our focus as it relates to the well being of our plants.

I see issues inherent in the plan described above, but can't offer a criticism as long as the focus is saving water. If the focus is on plant vitality, I see 2 substrate interfaces where perching is going to occur unless the expanded clay > .100 inch (.254mm) in which case there will only be perched water above 1 substrate interface.

Al

AL:

this is J0 just found you.Ireallyreally realy like everything on your blog.Im From Tx.and I dont know about all that stuff that goes in your grit mix.I THINK I know but not sure.Can you explain those ingredeance for me.As I have been looking for good soil for containers.MG is no good any more.Please help.

Jo - it's probably not a good idea to piggyback on Arcan's thread, but you can find a lot of info and get all your questions asked by clicking this embedded link and asking there.

Al

I dont know how to do that.

i am sorry if I did something rong,

Don't be disheartened and don't worry. All's well & I'm not scolding you. Everyone here wants to help you succeed. Normally, if you have questions, you would join in on a thread that is already discussing the topic you're interested in or start a new thread. If you click on the link I left in my post above, it will take you to a discussion already in progress on the topic you asked about, or for a wider variety of opinions, you could start your own thread. First, try clicking the link in my post above. It will take you to one of my threads. That's more polite than us starting a conversation in the middle of Arcan's thread. See you there!! ;-)

Al

Nil, I've never had salt accumulation problems with the mix I now use, but to be honest I've never tested salt levels as I've not seen any visual symptoms to be concerned (maybe I should anyway).

But I don't use water-soluble fertilisers - my base fertiliser is a good rock (basalt) based product with a relatively low N%, and an organic liquid product is used if growth needs to be boosted.

Hi Arcan, I couldn't find a way to contact you personally, but I like to know where do u source all the ingredients for your mix? I live in WA too and have problem finding them...

I thought I posted this on the gardenweb forum. Now it's houzz? Had to sign up for a new user name. Anyway soo - you can get the Naked Gardener Compost or Debco Premium Potting Mix from Masters (closing soon). Course Perlite is from The Perlite & Vermiculite Factory Myaree (much cheaper than anywhere else). Sand I got from a bulk landscape place (lawn mix) but you can get 10 or 20kg bags of builders sand at Bunnings. Zeochlor is in the pool section at Bunnings. Rock Dust I got from the manufacturer direct somewhere in Bibralake (called Natural PK) but I think but you can now get a similar product from Waldecks (in Myaree at least). Waldecks also sell bentonite clay.

I still want to try the gritty mix but getting my hands on all the materials has proved very difficult when I tried last year. I found a Queensland company that makes course DE (for mopping up oil/chemicals) but they didn't have a distributor in Perth. Nobody I could find has pine bark in the right size - and even if they did I'd have to by a cement mixer and modify it with a fine wire to screen it. Honestly, if an agricultural company were to produce the gritty mix and sell it in bags I think they'd make bank - even considering how long it lasts.