What does it say on the fertilizer label? All fertilizers will provide a dosage chart - it is a label requirement.

It says the amount for a 10x10 area which I am having trouble translating to individual plants.

Are all your starts in the same area? If so, about how many square feet does this area contain? If you can get to this point, you should be able to compare that area to the 100 sf area indicated on the label. Say for example your area is 3' deep and 8' long, that's 24 sf or about 1/4 the area specified on the label, so you would cut that dosage down to 1/4 of the amount suggested for the larger area (1C for 100 sf = 1/4C for 24-25 sf). Just sprinkle the amount evenly among the starts.

If the starts are scattered here and there, maybe a liquid fertilizer - something like Miracle Gro - would be a more suitable choice.

I'm using a water-soluble Miracle Gro and the plants are scattered.

From the label:

• With a Watering Can: Mix 1 tablespoon of Miracle-Gro® for every gallon of water.

For All Flowers and Vegetables: Use 1 gallon for every 10 square feet of flowers and
vegetables, every 7 to 14 days.

For Roses: Use 1/2 gallon for small bushes. Use 1 gallon for large bushes. Feed every 7 to
14 days.

For indoor plants, mix 1/2 teaspoon (not tablespoon) per gallon of
water. Apply every 2 weeks. We do not recommend foliar (leaf) feeding
for houseplants.