Answer: If you are using garden soil in the boxes I would suggest you switch over to a compost or peat based potting mix. These are much better for plants is containers (where root growth is limited) because their ability to hold moisture and nutrients while draining away excess water. The fair results you had this year could be due in part to the fact that there was garden soil in the boxes.
If the "soil" you sent in was a potting mix, I would question the applicability of the test results. Most soil lab tests are set to analyze a mineral type soil rather than an artificial growing media (potting soil). The results you get from a highly organic potting mix can be misleading.
Rather than trying to extrapolate down from the per acre rates, I would recommend you add a slow release fertilizer product according to the label directions to the soil or media in your boxes. You could also fertilize with a liquid fertilizer as the plants grow to keep them vigorous and healthy.
Thanks for the question!
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