? for Al T. Gritty Mix Preparation

briana_2006April 4, 2010

Hello Al -

Happy Easter! Hope all is going well.

I believe I have all the components and am ready to try to make a batch. I would like to make sure I have the process correct.

1. I believe you make a gallon at a time - so you would mix 1/3 Gallon Grit, 1/3 gallon turface and 1/3 gallon pine bark fines.

2. To the above mix add: 1 tablespoon gypsum and 1/4 teaspoon epsom salt

3. Once the mix is prepared to step 2 then mix all ingredients with a small amount of water - just enough to moisten the mix and then I need to let it sit for a while before using correct?

?: I had thought due to the acidity of the bark I needed to add lime?

2nd ?: The gypsum and lime I have is fairly powdery. Should I look for larger sized material since the powdery size may cause problems with too much water retention?

Side ?: If one were to (hypothetically) consider the decrease in the genetic growing potential of a plant in a peat based material is it possible to estimate the percentage decrease coming from problems with the PWT and compaction of the soil medium? I am just curious if for example all other things being equal does the PWT decrease the genetic growing potential by 50% and the compaction of the soil by 50% or is either of the factors much more important than the other i.e. 90% decrease due to PWT problem and 10% due to hard,compacted soils?

I could imagine that both are very important - with significant PWT - you get root rot and plant dies but with hard soil roots can't move and seek out nutrients. But if nutrients are being supplied by chemical fertilizer maybe compacted soils is less important - Since with root pruning you could keep the growth of smaller feeder roots in an active phase - and since nutrients are being provided the roots don't have to move through the soil seeking nutrients out?

Thanks again in advance for your help.


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tapla (mid-MI z5b-6a)

1) OK so far, but it's not necessary to make only a gallon at a time. I have a small utility tub that holds about 2.5 gallons, so I usually fill that level with each of the 3 ingredients & dump it into a mason's tub used for mixing mortar where I dampen it and mix with gypsum & anything else I might be incorporating

2) The gypsum (CaSO4) gets incorporated into the soil when you make it, but the Epsom salts (MgSO4) gets mixed into your fertilizer solution each time you fertilize. Use 1/4 tsp MgSO4 per gallon of solution if you're fertilizing at a reduced strength and at 1/2 tsp per gallon if you fertilize at full recommended strength.

3) Yes, mix while damp, but no need to allow the gritty mix with gypsum rest. Gypsum is much more soluble than dolomitic lime, so there is no appreciable reactive phase to take into consideration.

For most plants, you should use gypsum instead of lime in the gritty mix, but you can use lime for figs if you prefer. The larger pellets of lime and gypsum is the same product you are using, except that it's combined with a binder and 'prilled' so it's easier to broadcast (spread). The prills simply break up when they get wet. Also, you'll be using such a small amount of gypsum that it would be insignificant as far as any deleterious affect on soil structure.

Without some established controls, it's not possible to establish a comparison between a peat/compost/coir-based soil and something like the gritty mix. That isn't to say that there can't be a very significant difference, only that hard numbers are difficult to establish because of the number of variables. Your watering habits and any steps you might take to help mitigate the effects of accumulating salt levels play a major part in how clear the delineation is, but the very large number of GWers using soils like the 5:1:1 or gritty mix and happily sharing their results should be enough to confirm that for most growers the difference could be considered striking.

It's also difficult to separate the effects of compaction and PWTs because they are linearly related. Try to remember that media compaction and the accompanying lack of aeration produce stresses on the plant. Even if nutritional availability is significantly more reliable from ionic sources, supplying nutrients in that form won't noticeably relieve or negate the stress arising from other negative cultural conditions.


    Bookmark   April 4, 2010 at 8:20PM
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