Prepare your vegetable plot for sowing by digging out a trench to the depth of a spade. Fill the trench about a third full with well-rotted compost or grass clippings, then replace the soil to form a raised mound ready for sowing. Make sure you choose a sunny position with a solid trellis in place; against a wall or fence is perfect.
Plant each seed a half inch deep, spaced three feet apart and water the seeds in.
Train the stems of the trombone zucchini vertically up the trellis as they grow. Once established they will grow quickly and will benefit from a liquid feed every two weeks. Keep the ground around the stem free from weeds. The plants should start to bear fruit after about 60 days.
Harvest the zucchini with a sharp knife when they are 12 to 15 inches in length, if you want to eat the zucchini raw. Leave them on the vine for longer to produce a fruit with a firmer texture and thick skin like butternut squash.