Our onion and leek crop failed this year. Garlic was great. We are in south western Ontario. They are grown in full sun. Crops are rotated. Garden is watered occasionally when very dry. Soil is loam. Both were replanted once. Onions didn’t grow very well. Leeks seemed to shrivel up and die.
Leeks, garlic and onions are all members of the genus, Allium.
As vegetable gardeners in Ontario, we demand a great deal of growth and productivity from our plants, during a relatively short growing season. In order to produce and mature, therefore, our crops require a lot of water, nutrients and sunlight.
From what you describe, your plants have received plenty of sunlight. But as for water and nutrients – maybe not so much.
Your garlic seemed to do well, so let’s start with the onions.
To begin, make sure you select a cultivar that is adapted to Northern summers. This means selecting long-day varieties, which set bulbs when they receive between 15-16 hours of daylight.
Next ensure you plant your onions as soon as you can cultivate your garden. You can also start from seed indoors, 6-8 weeks before you intend to plant them outside.
Onions are heavy feeders, and require lots of nutrients to develop. Apply fertilizer before planting and side-dress 1-2 weeks after bulb enlargement begins. Organic fertilizers that work well for vegetable gardens include fish fertilizers, rock dusts, compost, compost tea and composted manure.
In addition, onions require lots of moisture. In fact, onion bulb size is directly proportional to the amount of water received during the growing season. Keep in mind, however, that while they require plenty of water, onions will rot if the soil is not well drained. A good layer of mulch can help ensure moisture is conserved and weeds are kept at bay. This is particularly important as onions don’t compete well with weeds.
Now for the leeks.
Generally, leeks come in two types: summer leeks, intended to be harvested in the same year they are planted and overwintering leeks, intended to be harvested the following spring.
Leeks have a long growing season and so are often planted as seedlings, rather than direct seeded. Plan to start indoors, eight weeks before planting outside. Make sure to plant them between eight and 12 inches deep to maximize the edible part of the plant.
Leeks are light to medium feeders. One way to ensure they get off to a great start is to incorporate organic matter into the soil prior to planting.
With their long growing season, mulching will help keep weeds out and moisture in. In the fall, protect your overwintering plants with a heavy blanket of straw. Leeks left to grow in the spring will go to seed and can be the start of a perennial leek bed.
Since your garlic did well, I will only mention that garlic is a medium feeder. Plant the cloves in mid-October so they have time to root, in soil that is heavily amended with organic matter.
I’ve included a link from the University of Maryland, with detailed growing instructions for your review.
Good luck!
https://extension.umd.edu/hgic/topics/leeks