When the plants are about 2 feet tall, apply 1 cup of fertilizer for every 10 feet of garden row. Scatter the fertilizer evenly between the rows and mix it lightly with the soil. Water after fertilizing. From Growing Sweet Corn by TAMU
Suggested times to side-dress vegetables
The following was extracted from here unless otherwise noted.
- Beans: not necessary.
- Beets: add bone meal or phosphorous at planting time; side-dress when plants are 4 to 5 inches tall.
- Beet greens: 2 weeks after leaves appear.
- Broccoli: 3 weeks after transplanting and again when heads begin to form.
- Brussels sprouts: 3 weeks after transplanting; again when sprouts are marble size.
- Cabbage: when the head begins to form; side dressing is not necessary if soil was well fertilized at planting.
- Carrots: add bone meal or phosphorous at
- Cauliflower: when heads begin to form; not necessary if soil was well fertilized at planting.
- Celery: 3 weeks after setting out starts; again 6 weeks later.
- Chard: after each cutting when substantial leaves are taken from plant.
- Corn: 3 weeks after planting or when plants are 8-10 inches tall; again when knee-high and again when tassels appear. [includes my edit]
- Cucumbers: just before vines start to spread and again when blossoms set.
- Eggplant: 3 weeks after transplanting and again at blossom time.
- Kale: when plants are 6-8inches tall.
- Leeks: when plants are 12 inches tall.
- Lettuce, head: a few weeks after planting.
- Lettuce, loose-leaf: after second and third cuttings for cut-and-come again crops.
- Melons: just before vines begin to spread; a week after blossom set; again 3 weeks later.
- Okra: Side-dress plants with fertilizer again when the plants are 6 to 8 inches tall and again two to three weeks later. Reapply the fertilizer every four to six weeks during the growing season. Apply additional fertilizer as a side-dressing if heavy rains occur during the growing season. Per SFGate.com.
- Onion: 3 weeks after setting out; when tops are 4 to 8 inches tall; when bulbs begin to form.
- Peas: not necessary.
- Peppers: 3 weeks after transplanting; again at blossom time.
- Potatoes: before second hilling; when plants bloom.
- Pumpkins: when plants start to run; again at blossom time.
- Radishes: no need to side dress.
- Spinach: when plants are about 1/3 grown; at second and third cuttings for cut-and-come again crops.
- Squash, summer: when plants are 6 inches tall; again at blossom time.
- Squash, winter: just before vines begin to spread; again at blossom time.
- Sweet potatoes: before second hilling.
- Tomatoes: 2 to 3 weeks after transplanting; at blossom time; before first picking; 2 weeks after first picking–always light on nitrogen.
- Turnips: add bone meal or phosphorous at planting time.
- Zucchini: at blossom time.
Side-Dress Applications of Nitrogen–From Mississippi State Extension Service here
1 pint of 34-0-0 per 100 feet of row, 3-1?3 tablespoons per 10 feet of row.
- Beans at 3- to 4-leaf stage
- Beets, carrots 4 to 6 weeks after planting
- Bell peppers, eggplant, tomatoes after first fruit set and again at 4- to 6-week intervals
- Broccoli, cabbage, cauliflower, Brussels sprouts 3 weeks after transplanting or after danger of late freeze in spring; broccoli again when heads begin to show
- Cucumbers, muskmelons, watermelons, winter squash when vines begin to run
- English peas when plants are 4 to 6 inches tall
- Irish potatoes when sprouts break through soil surface
- Leafy greens (mustard, turnips, chard, collards) when plants are about one-third grown
- Lettuce, kohlrabi, Chinese cabbage 2 weeks after transplanting; 4 weeks after sowing seed
- Okra after first pods are harvested
- Onions (green and bulb)—from sets when tops are 6 inches high —from transplants when established and actively growing
- Peanuts none
- Radishes none
- Southern peas none
- Summer squash before bloom when plants are 8 to 10 inches tall and again in 4 weeks
- Sweet corn when 8 inches high and again when knee-high
- Sweet potatoes none
- Turnips (roots), rutabagas 4 weeks after sowing seeds
- Tomatoes when first fruit are 1 inch in diameter; again at first harvest