Topic: Onion question

[Mrs Ava]

Should this go in the disease section....dunno....

My question is this.  Been browsing the catalogues looking at spring planting onion sets - lots to choose from.  Some are slower growing, maturing later, some fast growing maturing earlier.  Do you think the faster growers will have a better chance of beating the white rot which I have on my plot?  Do red onions fair better than white with the rot?  I wanna grow onions, really I do, but I don't want to waste money on sets to watch them all shrivel.

[tim]

If you look at the links on white rot, I think you'll find that the danger period is March-April for root attack. You'll have to draw your own conclusions! = tim

[Mrs Ava]

So if I plant sets in May I might get away with it?  How late is too late to plant though??  :-\

[Jill]

Don't know whether I was unlucky or whether this is what you could expect, EJ.  I was late putting in my onions and shallots 'cos first year an' all we didn't dig the beds in time.  Consequently both went in late April/beg May.  I harvested in August because they had stopped growing and had flopped over but they were decidedly smaller than they should have been.  Instead of starting later and finishing later, they'd cut down on growing time and stopped when they should have.  The very hot and dry July didn't help.

[Multiveg]

Maybe you could plant them in pots then transplant out later?

[tim]

'Disease section', Emma? I reckon, because there's more about it there, I think.
I'm out of my depth here but, without looking it up, it's the temperature in March-April when the roots are at a certain stage that's critical. HDRA & others give a full brief if you check the net.

Once it's there, I'm afraid that you're lumbered. You could try sterilising the new bed with Armillatox - the boss man there is confident of its powers, though it didn't work for me this year, despite meticulous application. I'm going for raised beds next year. = Tim

[Multiveg]

Thinking back to the article on white rot, where they apply composted onion waste which spurs the rot into germinating, but is unable to survive as the onion waste is not living.
How about in Feb/March, sowing some cheap spring onion seed, and then in April, or before, remove the seedlings (hopefully removing some of the white rot before it produces spores)?

From HDRA:

Once a white rot sclerotia has germinated and re-infected a new crop, it dies. If you know you have the disease, plant an Allium crop, wait for signs of infection to appear, then immediately lift and dispose of all the crop and surrounding soil. This might be successful in exhausting and removing most of the infection but would have to be repeated more than once.

[Tenuse]

I planted out my maincrop onions reeeaaaallly late this year (I was so embarrassed at how late they were, I pretended to the neighbouring lottie peeps that they were leek seedlings!!), but I got away with it by making a ton of paper pots, putting the seedlings into these and then planting the whole thing pot and all when the bed was finally cleared. They were a perfectly reasonable size when they were dug up (would have been bigger if my well-meaning mum hadn't "helped"!). Maybe this would also help with the onion rot thing?

Ten x

[tim]

Great thinking, MV - but God, what a bore!! = Tim

[Peter H]

Hi Tim, sorry to disappoint you but i use raised beds for my onions and they still got white rot, and this is with serilising the soil every year.
So next year all the soil is coming out and being repaced, will be hard work but apparently it takes 7 years to get rid of it.

Peter h

[john_miller]

Onions bulb up in response to shortening daylength. By getting the plants as big as possible prior to the critical photoperiod you will get bigger bulbs. Planting late outside will reduce the size of the plant by that time. Why not use large modules and transplant them after the risk of white rot is past EJ? Given enough fertiliser you can even grow 2-3 onions in one module, and plant them together, to cut down on the potting soil, hence the cost, of doing it this way.

[Mrs Ava]

I didn't realise that is how/why they bulbed up.  So really the sooner you can get them in, the bigger the onions will be.

It is a good idea starting them in pots, but for 150 sets I am going to need:
A)  lot of pots
B)  a lot of potting compost, and
C) a heck of a lot of room to grow them in !

However, that said, I do have the top of my compost heap which has a wooden lid and I could probaby fit 30 or so up there, so maybe do some as a backup, so if all else fails I have some healthy onions.

Thanks for all your advice.  Here's hoping for a white rot free 2005!  :-\

[john_miller]

Because onions (and all other members of Liliaceae) produce adventitious roots (which do not branch) their root system is quite poor. By multi-sowing seeds, or multi-planting sets, you will not affect their growth too much and stand a better chance of transplanting without excessive root damage (I have found their roots quite brittle). An alternative is too single sow/plant in pot/modules that are barely big enough so that the potting soil stays together.