How to Plant Onion Seeds in a Raised Bed

The bulbs of seeded onions do not grow very large the first year.

Onions are biennial vegetables, which means the plants grow green onions the first summer and form bulbs the next summer. The biggest advantage to seed-planting onions is the plants tend to bolt less often than onions planted from bulblets. Raised beds are perfect for planting onion seeds since it places the onions in an area with good soil that drains well and stays loose. Plant the onion seeds in the spring after the hard frosts are finished. Onion seedlings are frost resistant as long as the ground does not freeze around them.

Things You'll Need

• Raised bed frame
• Potting soil
• Sand
• Fertilizer
• Garden hoe
• Rake
• Onion seeds

Instructions

1. Place a raised bed frame that's 8 to 12 inches deep in a sunny area of the yard. Fill the raised bed with a mixture of 2 parts potting soil and 1 part sand or perlite. Mix the soil ingredients well so there are no distinct layers.

2. Sprinkle 10-10-10 slow-release fertilizer evenly over the raised bed. Use the rate of 2 lbs. for every 50 square feet of planting space. Work the fertilizer into the top 8 inches of soil with a garden hoe. Rake the soil smooth and level.

3. Create furrows 1/2 to 3/4 inch deep with the edge of the hoe. The trenches do not have to be very wide since the seeds are tiny. Space the rows 6 inches apart in the raised bed.

4. Drop the tiny seeds in the trench, spacing them 1 inch apart. Do not worry if they are closer, because they will be thinned later after they sprout.

5. Cover the seeds with soil and resist the temptation to firm the soil down over the seeds. Sprinkle the raised bed with water until all the soil is moist.

Tips & Warnings

• When the onion sprouts are 6 inches tall, start thinning the plants. Gently pull up every other sprout and use them as green onions. After the remaining seedlings have filled in the spaces, thin again until the plants are 4 inches apart. Onion bulbs will start to form and fill in the gaps.

• Weed the onion patch by hand to protect the roots and bulbs of the onions. Raised beds have fewer weeds than a normal garden, but the wind and birds can drop weed seeds into the bed. Do not mulch or pile up the soil around the onion plants, because the trapped moisture will cause stem rot in the developing onions.

References

• Clemson University Extension; Onion, Leek, Shallot & Garlic; Karen Russ; April 2003
• Plant Talk Colorado; Growing Onions from Seed; October 2003
• University of Minnesota; Growing Onions; Beth Jarvis; July 2001