It is your choice. Many of us swear by doing it, others say never do it. Try both and see what works best for you. Personally I have always trimmed the tops just as professional growers do as I proved to myself years ago that it stimulates new growth.

Dave

Dave: How about after they've been in the ground for awhile and the leaves start flopping over? Do you trim then also?

Kevin

The main reason I trim is to keep plants erect as much as possible. An onion plant that lays over may never recover. for the same reason you can't grow onions in a weedy bed- the weeds will prevent the more tender onions from growing upright and will eventually choke them out.

You will get a thicker stalk with more prunings and that will make transplanting that much more successful b/c the transplants won't be laying over and getting burned by the hot soil or plastic on the surface.

Pruning roots may help to get roots entirely in the soil and not sticking up in the air to dry. If you transplant through plastic this root trimming is more of an advantage. Since leeks can have an extensive root it may even be more advantageous to trim their roots than onions.

thanks for the explanation, bmoser.
Hmm . . . I went ahead and planted today and did not trim -- but I suppose I could cut the tops now (which are, as you say, lying all over the soil).
I made sure to cover all the roots.

Thanks Elisa but I don't know more than they do, I'm just older than the hills. :)

Kevin - yes I do just as bmoser said - thicker stems and bigger bulbs. But that's my soil and my climate and I grow primarily short-day varieties so your results may vary.

Dave

This is how the onion transplants arrived from - at least one mail order supplier - that I ordered from last year. They do not appear to have been trimmed on the tops or the roots? But - maybe they were trimmed when bundled and just shriveled up by the time they got to me? I did nothing but plant them the way they were shipped and the results appeared good - I may trim some of the transplants back this year and see if there is a difference in vigor and onion growth - I agree - that is the best way to find out if onions do better when the transplants are trimmed.

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I don't trim the tops when I grow from seed and the roots only get inadvertantly trimmed by me pulling them out of the flat to transplant. However, my seedlings are much smaller than the transplants you find in the store. Those things suffer from so much shock that in a month my seedlings will have surpassed them in size even though some of my seedlings look to be the size of a thread! Anyway, I'm generally happy with my onions as long as I remember to give them a good dose of N twice during growing.

Good to know, sunnibel.
My home grown seedlings are thinner than the mail ordered ones, and I'm interested in seeing how they do side by side.

Just look at the seedling picture posted by Hudson. All seedling growers trim them without exception. It is just too inconvenient to handle them untrimmed and it is not necessary. A 4 t0 6" seeding will grow back readily.

Of course if you do grow your own seedlings you cay choose not to trim or trim very little, if you just take them out of your own greenhouse and plant out in the field. Onion family plants are very tough and resilient.

Here are my Spanish onion seedlings, planted late Feb. I have kept them trimmed to 5-6 in. rather than trimming them before planting. As some have mentioned already, this is just to get a sturdier plant. The roots will self-trim as the containers are only about 3in deep.