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Sterilisation practices for seed propagation

By Anthony Meyer

Mar 2021

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Some finesses for dealing with contamination of seed raising mix, with particular reference to sealedcontainer germination. These notes apply particularly with seeds known to be prone to losses from disease in germination and might seem a bit excessive in general use. From personal conversations with Masumi Robertson. My apologies to Masumi if I’ve made any errors!

 Boiled Water

 Keep in sealed co ntainers, use for all watering  

Seed Raising Mix

 Perlite: Peat moss 6:1 (NOT coir) pH 6 Experienced local nursery propagator, Peter Ollerenshaw, insists that ‘Cocopeat’ is not effective (Masumi). Source peat responsibly!

Seed Surface Sterilisation

(Works for cutting material as well) Commercial Chlorine bleach diluted 1:4 (= Na Hypochlorite 4.2% — pool chlorine) Soak for 10 minutes then rinse off with boiled water.

Pasteurising Propagation Mix

1. Pour one kettle (~ 1.5l) boiling water into a container, enough mix to do maybe 2 x 750 ml punnets.

2. Drain off immediately

3. Aim is to get the whole mix hot.

4. 2. Pour more boiling water into container till whole mix is 65 — preferably 80°C (no need to check!)

5. Cool covered

6. Microwaving leaves cool spots (Masumi)

Sealed Seedling Boxes

Keep sealed till cotyledons are pushing on the lid, harden off with the lid ajar. I find that it is at this point that some pathogens, like damping off, appear in earnest. My solution is to bottom water the punnets, as I have described before.

Disinfecting

 Tweezers and Cutters — Methylated Spirits Diluted 70% with water (mostly Ethanol anyway). *A note about sharp nicking of hard testa seeds like Acacia and pea genera to break dormancy. Nick the end of seed opposite the ‘aril’, a small waxy attachment on the seed, to avoid injuring the embryo (Masumi). Pour on very hot but not boiling water and cool.

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