If you can find them, aged pine bark fines are the best choice for the 5-1-1 mix (bark/peat/perlite). The finer particles will hold more water, and aged bark will tie up less nitrogen than fresh bark. If you're unable to find aged bark and you're concerned about water retention, you might consider increasing the amount of peat in the mix (4-2-1, for example). You can work around any potential N immobility by increasing fertilizer rates (if necessary).

So would two 1/4" pieces of bark retain more water than one 1/2" piece of bark?

Is that because of surface area?

Yes, more surface area equals more water and nutrient holding capacity.

This post was edited by shazaam on Mon, Aug 26, 13 at 20:48