Saturday, 16 September 2017

Use of Salt-Petre for Soaking Stubborn Seeds

Use of Potassium Nitrate as a Germination Aid

Potassium Nitrate (KNO3) is a well known useful aid to help the germination of particularly tricky seeds - in the main those which have a coating or chemical in the seed which delays or prevents germination.  Such seeds will only reliably germinate once this chemical is removed.  In nature this may be due to the seed being eaten and passing through unharmed but with the chemical stripped due to digestive enzymes and chemicals or perhaps as a result of weather (rain, snow or frost) or just time.

As gardeners we like a degree of predictabilty and this is where Potassium Nitrate comes in.

The action of the solution on the seed denatures germination inhibitors and softens the seed coat to all water in and the process to start more evenly.  Anecdotaly seeds, such as Banana, have been known to germinate erratically over many months (if at all), yet with treatment, this period can be as little as a month and all the seeds come up.

To use the powder

You will have a sachet of 1 teaspoon of KNO3 (5 grams).  This can make up to 8 litres (around 8 qts) of solution depending on the required strength.

Full strength - 5g per litre
Half strength use 2 litres and so on down to 1/8 strength.

All seeds that are problematic will benefit from a soak.

For Musa, Ensete, Musella (Banana species) use full strength - you will see it written in some places that a very dilute solution works, well good luck with that, most sources and our experience suggests only full strength will work properly - 6 hours
For Chilli seeds that have been open pollinated use 1/2 strength - 3 hours

For Opuntia seeds (Prickly Pear) use full strength - 6 hours

For Michelia use full strength - 6 hours

For Acacias and other tree like members of the pea family use 1/8 strength if you do not use the boiling water method in those instructions - 24 hours, then use plain water

For Bamboo seeds use 1/4 strength - 24 hours

The powder should be mixed with warm water (40 Deg C or 105 F) and stirred or shaken to fully disolve.  Only use plastic or ceramic for mixing never metal.  The solution may be stored in a sealed container for many weeks without issue, just make sure you mark what is in it for safety reasons.

The soaking period varies for each type of seed, in general the weaker the solution, the longer it can be left.  As a rule of thumb, the shortest soak should be 2 hours, the longest 24 hours.  Those that require further soaking, this should utilise plain water after the intial treatment.

After treatment, sow the seeds as per the instructions for that species.

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