Whether you use the board or not ( I recommend it), you're going to need to dig the trees regularly and work the roots. Tridents have a tendency, when ground grown, to only develop a few very large roots which will, in turn, produce an unbalanced and ugly nebari. I've found that going 3 years between digs is actually too long... but the good news is they truly grow like weeds and will still develop very fast. Fwiw, if you're truly interested in growing a shohin, you may want to skip the ground growing entirely and stick growing in a container- wooden box or anderson flats were made for this sort of thing- where you'll have more control over everything. In my experience, tridents grow so quickly in the ground that it's very difficult to produce a nice shohin trunk- read that as a trunk without a large chop scar