Catawissa Onions can attain a height in the ballpark of 5 feet, but generally average around 3 - 3.5 feet.
The topset Onions emerge in spring encased in a papery husk which eventually drops off of its own accord as the plant matures. They reach full maturity by late summer. They do at times produce some white flowers that are about 1/4 inch wide, but they are usually short lived and crowded out by the onions.
Because they do not produce very many flowers - which is what produces the seeds - walking onion seeds can be hard to come by. They are generally propagated by onion sets.
Planting walking Onions from sets does not differ from planting standard onionsSee - Onion Planting Guide
Unharvested topset onions that lie on the ground will self-sew and reproduce naturally. No re-planting is necessary once you have an established patch.
Egyptian walking Onions can be planted in either the Spring or Fall.
Walking Onions planted in the spring will produce a crop the same season by summers end, planted in the fall they will produce a crop in the following season. Some people also plant them in the summer, they will generally produce foliage in this scenario and the subterranean bulb and roots will develop but they rarely produce any top-set onions till the subsequent season.
If you plan on growing these as a perennial, season after season in the same location more careful attention needs to be paid to fertilization early in the season. The previous seasons crop[s] used many of the nutrients the plants require, fertilizer should be replenished.
The best time to pick the topsets is once the stalk has browned a bit, in late summer. Most will have toppled over by this time, leaving a few on the ground will ensure additional plants come next season.
The greens are also edible are are cut and harvested at any time of year. Harvesting a few leaves from a healthy plant is feasible without detrimental effects on the plant as a whole. Be certain to harvest only the leaves - not the stalk that is producing the top-set onions.
Harvesting the subterranean onion bulb can be done in late summer and fall. This should only be harvested if you do not plan on having the plant regenerate next season.
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