Post Harvest Treatment

If left untreated the petals will drop from cut delphinium flowers in 4 or 5 days. If treated in STS solution, flowers should last up to 3 weeks with regular fresh water and feeding.*

The STS solution I use for delphiniums is made as follows:

  • You need to make up a concentrate solution. To do this you need 14gms silver nitrate and 80gms sodium thiosulphate per litre of concentrate. I suggest making up 5 litres.
  • To make the 5 litre concentrate you will need two plastic stirring rods (alkathene pipe is good) two clean plastic buckets, one in which to dissolve the silver nitrate and the other in which to dissolve the sodium thiosulphate. Please note, you cannot dissolve them together in the same bucket or it won't work.
  • In one bucket, dissolve 70gms silver nitrate in about 2 litres of water. This will take a few minutes stirring.
  • In the other bucket, and with the other stirrer, dissolve 400gms sodium thiosulphate in 3 litres of water.
  • When both are dissolved poor the silver nitrate solution slowly into the sodium thiosulphate solution while stirring with the silver nitrate stirrer. The silver nitrate solution will turn milky white as it hits the sodium thiosulphate solution but quickly disappear to leave a clear liquid. This is your STS concentrate which should be stored in a black plastic container and kept refrigerated.
  • Take care not to splash the silver nitrate solution around (on skin or clothes) as it quickly turns black and cannot be easily removed.

I use the concentrate at a rate of 60 mils per 20 litres of water and add 15 mils of  bleach as a biocide. Delphinium must stand in this for at least 12 hours (overnight in the cooler) to give effective post harvest treatment. You may re use the diluted solution several times.

I found that making my own STS in this fashion was many times cheaper than buying a proprietary brand and at least as effective. Use of this formula is at your own risk and although it has worked for me for 12 years I accept no responsibility for it's use by anyone else. STS is sometimes known commercially as AVBs

Terry Dowdeswell

*(you can use either a commercial cut flower food or a homemade mixture of about 1 heaped tablespoon of  sugar and 1 teaspoon of bleach per half bucket of water - the sugar feeds the flowers and the bleach stops bacterial growth which would also feed on the sugar.)

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Dowdeswell's Delphiniums - Wanganui, New Zealand