Vermiculite

David R. Hershey dh321 at excite.com
Sun Feb 15 19:43:57 EST 2004


Vermiculite is not good for mineral nutrient deficiency studies because
it has substantial quantities of potassium, magnesium and some
micronutrients. I once grew potted chrysanthemums in a 50%
vermiculite/50% sphagnum peat moss mixture using just the potassium in
the vermiculite. They grew fine. Bunt (1988) says vermiculite samples
average 5 to 8% available potassium and 9 to 12% magnesium.

When I handle bags of perlite, I first cut open a corner of the bag.
Then I use a spray bottle of water and generously mist inside the bag to
wet down the dust. Use distilled water if you want to do mineral
nutrient deficiency studies. When you open the bag, continue to use the
spray bottle as necessary. Pure perlite is nice to root cuttings if you
want to bareroot them easily.

For most mineral nutrient deficiencies, especially macronutrients,
sphagnum peat moss or a peat-perlite mixture would probably be
satisfactory. The peat moss greatly increases the water holding capacity.
 
I like solution culture for mineral nutrient deficiencies because the
root system is visible. Solution culture clearly disproves the common
misconception that plants "eat" soil. The houseplant, piggyback plant
(Tolmiea menziesii) does well in unaerated solution cultures for mineral
nutrient deficiency demonstrations. Piggyback plant is nice for solution
culture because it is clonal plus it requires no staking. The foliar
plantlets root easily in solution. Two-liter soda bottles with the tops
cut off at the widest diameter can be used as reservoirs. To provide
some aeration, the top 2 to 3 cm of the root zone is kept above the
solution. 

It is also an iron inefficient plant. When given a nutrient solution
with all nitrogen as nitrate and no iron chelate, it becomes iron
deficient even if the roots are coated with powdered iron oxide (Hershey
1991). Many other plants would lower the solution pH under those
conditions and solubilize the iron. 

References

Bunt, A.C. 1988. Media and mixes for container-grown plants. London:
Unwin Hyman.

Hershey, D.R. 1991. Iron deficiency stress response of Tolmiea
menziesii. Journal of Plant Nutrition. J Plant Nutrition 14: 1145-1150.




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