Top dressing for Onion sets

[morgan_h6]

For many years I have been using Nitro Chalk as a top dressing for my onion sets, I have 180 sets and use 6oz per dressig during or before rain.The sets must have started to bulb before applying. The sets usually keep into the following spring.

[farmer jon]

this seems a very heavy dosage to me & at a strange time. I would only feed before the bulbing has initiated & with a slightly less strong hit of nitrogen such as nitrate of soda. the problem with over feeding onions with nitrogen is that it gives them thick necks resulting in poor keeping quality. I never feed during the growing season but prefer to incorporate all fertiliser into the onion bed , part during winter digging & manuring & part prior to planting. the idea being that the more leaf growth prior to bulbing ,the better the onion size. I have grown on the same bed for 30 years so the fertility has built up.

[Geoff]

Onion feeding is a bit of a mystery. Traditionally you give Nitrogen for leaf, Phosphate for root and Potash for fruit but what is an Onion? It houses a flower bud (and doesn't always keep it in the house!) so perhaps it is a swollen flower bud, I should know this. This suggests Potash rich feed. However, it is also said that the amount of leaf you can get before the day length reaches 16 hours the better the bulb. Reading books they usually say use previously manured ground but fertiliser suggestions vary. "Know and Grow Vegetables" suggested a medium dose of Growmore 4 oz/sq.yd. whereas "The Vegetable Garden Displayed" says 3 oz Superphosphate and 1 oz Potash. I have an odd rotation that puts Onions after Potatoes (Leeks go in after the Earlies then Japanese Onions and ordinary Onions follow), I add some Growmore, Superphosphate and Potash, if it is dry I give the odd watering with Phostrogen. I would think Nitro Chalk would be wrong when ever it is applied.

[njh1961]

My 83year old father is insisting I sprinkle caustic soda around the onions on my allotment! He is obviously wrong, but he says his uncle used to grow giant onions that were very strong tasting, and he did this. Does anyone have an idea what my father is getting confused with? I am running out of excuses and am worried he may go and do it behind my back. Thanks

[Geoff]

Potash is the normal Onion feed but the only thing I can find that sounds anything like Caustic Soda is Caustic Potash - Potassium Hydroxide rather than Sodium Hydroxide but I can't imagine it is ever used as a fertiliser. The clue is in the definition of caustic:
"Capable of burning, corroding, dissolving, or eating away by chemical action"
You'll have to persuade him that he means normal Potassium Sulphate!

[njh1961]

Thanks, I will try that. He usually listens when I tell him I have done research on the internet.

[Stonecoloured]

He usually listens when I tell him I have done research on the internet.

That's usually when my SO ignores what I'm saying LOL

[njh1961]

Success! Tactfully told him that I could find NO information on the use of caustic soda to enhance onions and that potash sulphate was the normal thing used. He thought for a bit and said "The spiteful old sod! Uncle Bill must have been making sure I couldn't grow onions as big and nice as his." We went to the garden centre and bought a 1.5 kg box of Westland Sulphate of Potash Fruit and Flower Food - so the caustic soda idea has finally been put to bed......hopefully.