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2001 Paul Barlow


Soil Sterilisation and Compost mixes

In 1998 I decided to sterilise the main components of my potting mixes. With a ready supply of stacked turf and garden compost, plus the out turn of 100 or so pots of earlies and lates from the previous season, here was an opportunity to recycle and revitalise my potting mixes.

I purchased a steam sterilisation bucket and also managed to borrow another from a friend for the several weeks that sterilisation was carried out. Each bucket holds about 2 gallons, so running them side by side enabled me to sterilise about half a bushel at a time. The process takes approximately 25 - 30 minutes, but with perseverance over several weekends and evenings I soon had sufficient sterilised materials for the entire season.

bucket1.jpg (19454 bytes) bucket2.jpg (17051 bytes)

The pictures above show the steam sterilising unit. The bucket sits on top of a pan of water that is heated using a conventional electric element. The steam finds it's way through the perforated cone that forms the base of the bucket and onwards through the soil. The lid for the bucket has a small hole in which a thermometer is inserted to keep an eye on the soil temperature.

Sterilisation is complete when steam emerges from around the lid on the top of the bucket. By this time the soil temperature will be approaching boiling point. The soil is then spread out and cooled before bagging and storing for several weeks, after which it is ready for use.

Sterilisation is not without it's complications. There can be adverse effects related to soil sterilisation so a little research was required to make sure that only the beneficial effects were transferred into the growing routines. For instance, experiments have proved that lime added after sterilisation is far more beneficial than when added before, similarly superphosphate is added after sterilisation to counter the retarding effect of excessive ammonia produced during the steaming process.

This is now a new annual task for me following good results during the 1998 season.


Compost mixes After re-reading Ivor Mace's book on Lates I decided to change my compost mix to something a little stronger. As I mentioned on the Just Starting page, propagation is carried out using soilless compost with perlite added to the mix. Subsequent stages make use of the sterilised materials described above. The basic mix for 1998 was as follows (per 80 litre mix):

40 litres sterilised soil.
20 litres sterilised previous years potting mix
20 litres fresh peat
Coarse grit added until the mix feels right, typically between 5 and 10 litres.

Fertilisers are added per 80 litres, the amounts depend on the stage of growth and pot size being used:

Fertilisers

3.5" pot

5-6" pot

Final pots

Superphosphate

1.5 oz

2 oz

2 oz

Lime

2 oz

2 oz

2 oz

Vitax Q4 (NPK 5.3-7.5-10.0)

3 oz

6 oz

8 oz

Growmore (NPK 7-7-7)

3 oz

6 oz

8 oz

Calcified seaweed

-

6 oz

6 oz

6x Concentrated manure

-

-

5" pot


If you would like further information or wish to comment on this publication please send your e-mail to: paul.barlow@chrysanthemums.info

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Last updated on 10 November, 2005