A good general rule of thumb (green, I hope) for all trees is a uniform mix of loam, peat, & sand. A good compost (the mix) should be a well-balanced one. The proportions of each will change according to the species of tree. For instance pines & junipers will prefer a mix which is principally sand; rhododendrons & azaleas like a peaty compost; while fruity & flowering trees like plenty of loam. A good suggestion would be that you try to match the original soil(s) the tree came with, if possible, if not the following chart will help; NOTE: The sand should be a coarse grit like substance to promote good drainage!
TYPE SPECIES SAND PEAT LOAM
General mix Most varieties 2 1 1
Pine/Juniper 4 1 0
Conifer mix Cypress, &
other conifers 3 1 1
deciduous mix 2 1 1
Fruit/Flower mix 1 1 2
Lately I have been experimenting with soil mixtures, which seems to be the best way to understand soil mixtures. And it became quite obvious to me that some of my trees had been set back a years growth because the soil wasn't right . . . there was very little new root growth. And when I transplanted it into a good mix the new root growth was triple the amount of old root! The importance of good drainage cannot be emphasised enough as the roots require some air too! I have been covering the base of the pot with small gravel and then the putting the proper mix for the particular tree and to top it off a finely sifted loam to promote moss growth. A proper soil mix will allow for drainage while holding enough mosture for the plant without causing root rot, etc.
(Note: The fine soil on the top should be a VERY thin layer and is only really there to allow moss a good footing.)
Experimentation and observation is the best way to find the right soil mix for your tree(s). If you are in doubt use the above mentioned 'General mix'. Pines and junipers can be as much as 70-80 % sand!
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