Earthbox is designed to have 2 cups of synthetic or 3 cups of organic GRANULAR, DRY fertilizer added along with about 2 cups of dolomite lime at the start of each growing season. Did you follow the start up instructions when you set up your box? If so you would not need to add additional fertilizer.

This is the second year for the earthbox and I didn't order the fertilizer strip again. How much Triple 13 (granular) should I add to a gallon of water?

Linda answered your question.

Add the granular fertilizer strip on top of the mix without water dilution.

You certainly don't need to order your ferts from Eartthbox every year. Any granular fertilizer with numbers between 5-15 will work. It is important to add the dolomite lime however as over time the growing medium will become acidic.

Since you didn't add the fert strip why do you feel you can't add it now? If not for some reason then you will have to feed the plant weekly with a liquid fertilizer of some kind. Many of us that use Earthboxes give it a liquid fert boost every couple of weeks anyway even with the fertilizer and lime strip in place.

But yeah you can't expect them to do well without some sort of feeding. Your big problem will be that you have two plants with different nutrient needs in the same box.

Dave