One bunch of onion plants (60- 75 plants per bunch) will plant 10 feet of double row if they are spaced 4 inches apart. If space is in short supply, plant the onion plants 2 inches apart, and thin them as they grow and enjoy every other one as a green onion. Leave the remaining onions until maturity at a spacing of about 4-6 inches.
Ten Ways to Ensure a Great Onion Crop
1. Plant a recommended variety for this area from November through February.
2. Keep your plants in a well-ventilated, cool area until you can plant.
3. Keep plants dry until you can plant. Do not put them in water.
4. Fertilize before planting as well as during the growing season.
5. Choose a location with good drainage and full sun.
6. Water thoroughly after planting and regularly during the growing season.
7. Don't plant too deep. One inch is plenty.
8. Keep your onion bed weed free.
9. Keep the soil loosely cultivated around the onions when they begin to bulb.
10. Harvest the onions as soon as the tops die down so they do not rot.
How Should I Prepare My Onion Beds?
Onions grow well here in double rows on raised beds about 4” above grade and 16”-20” wide. They are happiest in loose, fertile, well-drained soil with plenty of organic matter. Soil with a pH between 6.2 and 7 is ideal, but soil here is considerably more alkaline. Add organic material, such as peat moss, compost, or manure and use sulfur to help lower the high pH of our soil in Wimberley.
Onions require a steady supply of nitrogen, and extra phosphorus. The best time to provide these essential nutrients as well as other micronutrients is prior to planting, so the nutrients will be readily available in the root zone when needed. One way is to make a trench along the center of the row and distribute ½ cup of 1-2-1 ratio fertilizer per 10 linear feet of row, cover the fertilizer with 2 inches of soil, and plant onions within 6 inches of the trench. Repeat at three weeks and six weeks of growth, or at 6 and ten weeks for slow-release fertilizers.
Organic gardeners will want to use an organic fertilizer with a good organic source of nitrogen. I recommend cottonseed meal or blood meal. Bone meal and rock phosphate are good organic sources of phosphorus. Use trace minerals or Medina soil activator to make sure all your micronutrient needs are taken care of. All of these are most effective when thoroughly mixed into the soil before planting. Repeat feedings are not necessary with properly enriched organic gardens.