How to Plant Onion SetsThe first thing you should do when planting onion sets is to amend the soil well with compost and organic matter where you intend to grow the onions. Onions enjoy fertile soil with very good drainage. Soil drainage is important for onions because if they stay too moist they could rot or mold could form on them. Once you have the soil ready for planting remove the onion sets from the bundle or bag, and lay them out on top of the garden bed in the location where they will be planted. Onions do not need much spacing (depending on the variety) and can be planted fairly close together - about six inches apart. Here, I am laying these 'Exhibition' onions out with six inches of spacing in all directions. If you want to grow the large onion bulbs then space them at least six inches apart. If you are interested in using these as green onions, then space them as close as three inches apart. Spacing them out like this will help to speed up the time it takes to plant. You will not need to measure the spacing out for each onion because it will be already in its spot. I hope that makes sense... So, with the onions spaced it is time to plant them. These 'Exhibition' onions need to be planted about one inch deep. Make sure to read the instructions that should be provided with your onion sets for proper planting dimension for your particular variety. Simply take your finger and poke a hole in the soil about an inch deep and place the onion into the hole. If you are using the sets that are just bulbs make sure the pointy tip is facing up when planting. With the onion in the hole work some soil around it and gently firm the soil up with the palm of your hand. Don't mound too much soil up around the onion. Just enough to "fill" the hole and stabilize the onion set. Continue these same steps throughout the bed until you have all the onion sets planted. Once you have all the onions planted make sure to water them well. Give them a good soaking each day until they begin growing new green tops, then you can cut back the watering to every other day (depending on how much rainfall you receive). It's also a good idea to mulch around your onions to help suppress weeds, preserve soil moisture, and keep the onions cool during those very hot summer days. If you don't have an extra bed for growing onions, you can interplant them with lettuce, kohlrabi, and tomatoes. Avoid planting onions with peas and asparagus.
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