Bean family
Beans, Southern peas, and green peas: light-medium feeders; side-dress beans, if necessary, when pod set is heavy. Excess N delays flowering. Plants produce some N for their own use but peas produce less than beans.

Beet family
Beet, Swiss chard, spinach, callaloo: heavy feeders

Cabbage family
Brussels sprouts, broccoli, cauliflower- heavy feeders; side-dress 3 weeks after transplanting (side-dress broccoli a second time after central head is harvested to encourage small heads on side shoots).
Cabbage, kale, turnip, collards- medium feeders; side-dress 3 weeks after transplantingRadish: light feeder; avoid excess N.

Carrot: light-medium feeder.

Lettuce: medium-heavy feeder; romaine and crisphead types may require side-dressing.

Okra: heavy feeder; side-dress after first fruits form.

Onion family
Onion and garlic: heavy feeders; side-dress onion once as bulbs enlarge and side-dress garlic twice- mid-April and mid-May.

Leek: light-medium feeder; side-dress in May or June.

Squash family
Cucumber, squash, melon, pumpkins: medium feeders; side-dress when fruits start to form.

Sweet corn: heavy feeder; side-dress when plants are 12-18 inches tall and when plants start tasseling.

Sweet potato: medium feeder.

Tomato family
Tomato, tomatillo, pepper, eggplant, potato: heavy feeders; side-dress when fruits or tubers first form. Epsom salt (magnesium sulfate) does not prevent blossom-end rot. Don’t add it to the soil unless soil testing shows a magnesium deficiency.

Perennial crops
Asparagus, rhubarb, horseradish: medium-heavy feeders.
Prior to planting, prepare the bed as early as possible and enrich it with compost and/or manure. Apply one inch of compost around plants yearly.  Fertilize in early spring and after harvest if needed.

Additional resources
(PDF) University of Connecticut – Fertilizer Conversions
(PDF) Louisiana State University – Tons to Teaspoons

An excerpt from the article “Fertilizing Vegetables“, by Jon Traunfeld, Director HGIC, Extension Specialist, Fruits, and Vegetablescourtesy of the University of Maryland.