After water, nutrients rank as the most probable limiting factor in plug production. Fertilization is vital since the small core of propagation medium in each chamber is unable to offer much to the new plant. Major and minor elements are both critical. Low nitrogen fertilizer (about 50 ppm) can be applied at the time of seeding, with concentrations increas-
ing as the seeds germinate and begin to develop. Local problems such as high soluble salt levels or pH extremes (outside the optimum 5.8 to 6.0) need to be addressed as well.