Hi..

Did you ever try sunflowers?
No. I guess it works the same way there too?

Many years ago they sold "bonsai sunflower pot sets": A
small low flower pot, a "steel bag" woven of thin steel
filament as big as a tea bag for making a single cup of
tea, some earth and sunflower seed. Well, I bought two of
those sets, put earth and seed into the little steel bag,
put the steel bag in the flower pot, filled the flower pot
too, watered the pots, waited 2 weeks without any result.
So I went to the garden centre, bought fine earth, removed
the old earth, took seed from my garden sunflowers that
generally grow up to 2m and repeated the procedure. I
finally had bonsai sunflowers.

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cu
Marco