Roots don't really push through the medium - they grow around the soil particles & then expand.

Use gypsum as the Ca source, as pH of the Turface/granite mix will be slightly higher than that of the same mix w/bark included.

I grow lots of plants with a very small or no organic fraction, so the screened Turface/granite mix is fine. If you're noticing slow growth, it's probably because you're not providing enough nutrition (not fertilizing often enough or at a high enough concentration), or there's a hole in your supplementation program (an element missing that's inhibiting growth).

A copy/paste from something I wrote earlier: Liebig's Law - Certainly some of you have come across this before. First, there are 6 factors that affect plant growth and yield; they are: air water light temperature soil or media nutrients. Liebig's Law of Limiting Factors states the most deficient factor limits plant growth and increasing the supply of non-limiting factors will not increase plant growth. Only by increasing most deficient factor will the plant growth increase. There is also an optimum combination of the factors and increasing them, individually or in various combinations, can lead to toxicity issues/reduced growth.

Al

With the heat in the upper 90s now, is it possible that the Osmocote that I add into the mix is being entirely used up in two months or fewer? The bag says "feeds up to 4 months", but since more nutrients are released at warmer temperatures that might not be accurate. Also, because I don't fertilize during watering, the plants don't get much magnesium (from Epsom salts). Could that be the problem?

Never tried using only granite and turface without the pine bark. Would you mix granite and turface at 1:1?

I'm growing maples and pines so if I used this mix would I adjust the mix at all or use a 1:1 mix for both?

Assume Id still use gypsum, correct?

Thanks!

I have one bulb in a 1:1 experimental mix and it's doing fine. It really depends on whether you want a faster draining mix that's less water-retentive, in which case you could do 1/3 turface : 2/3 granite, or whether you want it to be more water-retentive, so 2/3 turface: 1/3 granite, and use a wick if necessary to drain extra water.

YK - is there Mg in your fertilizer?

Let your plants tell you if they need more fertilizer - watch for chlorosis, particularly in older/lower leaves. If you see it, and are sure it's not the result of something else cultural, it's a good bet your plants need fertilizer.

Pardak - you would still use gypsum.

Al

Al: only in the micro-nutrient fertilizer, which I add at the rate of 1/2 tsp per 4 gallons.

Thanks ykerzner and Al. Sounds like this might be a good experiment. Many of the people here have problems finding pine bark in the correct size, so maybe this would be an idea for container gardeners who dont have access to pine bark fines.

So I would add the gypsum, just like the regular grit mix, but I can adjust the granite/turface ratio depending on desired moisture levels. For maples I'd probably use a 1:1 ratio, but for pines I'd use maybe 2 parts granite to 1 part turface. Sound about right?

Also, could I substitute screened NAPA Floor Dry for turface in this soil mix? The soil would be mostly light gray or white which might help keep the soil temps down in the hot summer months.

Thanks again.

I can not resist commenting on the Osmocoat that can provide fertilizer for "up to four months". Of course that is true, it is possible. It is also possible each of us could live to 100. Possible but less than likely. I use a timed release fertilizer in all my containers from four inch up. I like it because of its release of nutrients being tied to the temperature, which corresponds to the rate of plant growth and the plants need for matching fertilizer. However I do not rely only on timed release because I want to even out the availability of plant nutrients whether used or not and so Foliage Pro is also used on a regular schedule. This year a group which I am affiliated, in another town, which precludes my being more active, grows thousands of plants for a 1000 sq. foot fair display. This year in northern California the summer has been so cool many of the plants were not mature enough by fair time. It is my belief that if a supplemental liquid such as Foliage Pro had been used the plants would have reached their normal size. Al

YK - Assuming you don't have a water(ing) issue - I would watch for yellowing of foliage. If that occurs, first spray some of the foliage with a weak solution of Epsom salts. If the chlorosis goes away/improves, it's a pretty sure bet your plants need more Mg than you're giving them. If it doesn't go away - fertilize, because it's likely they need N. If THAT doesn't work, adding an acid to your irrigation water should improve availability of micro-nutrients which would be the next logical suspicion.

Pardak - (not snotty) you guys have the information and understanding about what makes a good soil. I'm not selling a soil, just a concept - great aeration for the life of the planting. Feel free to experiment. If something doesn't work out as well as it could, you already know how to fix it. ;o)

Your ratios make good sense to me - so give them a try & stay in touch with us. I grow some plants in an ALL inorganic mediums, so I know it can be done well. You just need to stay on top of nutrition because the bark fraction does offer a little bit of a forgiving cush in that regard, though not all that much where the gritty mix is concerned.

Al

Thanks for the reply Al. Just wanted to make sure I was understanding everything clearly. As a test I will pot up both a maple and a pine in this inorganic mix of granite and Turface (plus gypsum) and report back. It's probably too late in the growing season to repot anything now so I will wait until next spring. I may also try using the NAPA Floor Dry (DE) in place of the Turface just to see what happens.

I have some screened pine bark on hand but this inorganic mix might be a good suggestion for those who cant find pine bark in their area.

Speaking of pine bark, I've noticed that most of the garden centers in my area are now clearing out all their garden supplies, including soils, mulch and bark, so finding pine bark now may be tough in some areas.

Thanks.