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Propagating Plants for Hydroponic Growing

Plants properly propagated by conventional methods are quite suitable for use in NFT and bag growing hydroponic systems. Avoidance of root damage when transplanting into hydroponic systems greatly assists plant establishment and it is highly desirable that plants should be grown in individual pots. Plants can be propagated in ordinary disease free propagating media such as peat, bark or mixes of peat or bark with pumice,sawdust sand mixes, coir or rockwool cubes. It is not necessary to propagate plants in inert media, although it may be desirable to do so if disease free potting composts are not available. It is not necessary to wash roots clean of bark or peat before planting in NFT systems, and doing so often does more harm than good.

Adequate nutrition during propagation is vital for success. Many seeds absorb nutrients during their initial imbibition of water prior to germination, and it is important that the seed sowing media has a normal content of nutrients. Attempts to germinate seeds in inert nutrient free media often result in seedlings which remain poor and hungry looking throughout their propagation period. Much stronger seedlings result from germination in mixes with half strength additions of potting mix fertilisers

Seedlings can be pricked out into either a normally fertilised mix or into an inert media. Seedlings in inert media will need regular watering with complete nutrient solutions throughout the propagating period, seedlings in fertilised mixes may only require liquid feeding with NPK solution towards the end of the propagating period.

Pots which allow free growth of roots out into the NFT nutrient solution or into the bag and which do not need removing from the plant at planting out time are best. Paper pots (grade VS size 808) or peat or fibre pots about 75 diameter or square and 75 mm deep, or similar size bottomless plastic pots or rockwool or coir propagation cubes (75 x 75 x 100 mm tall) are ideal. Ordinary plastic pots can be used for propagation but the pots have to be removed when planting out. This is quite satisfactory as long as the plants have established a good root system to hold the ball of potting mix together. The use of larger pot sizes does not appear to offer any benefits and may delay the establishment of an extensive root system in NFT gullies.

Original 1997 revised 30/9/99

A General Purpose Potting Mix.

This potting mix is suitable for propagating a wide range of greenhouse crops, including tomatoes, peppers, cucumbers, courgettes, melons, lettuce and many ornamentals.

The mix can be made from 100% peat (good quality peat such as Hauraki peat), or composted fine ground bark. Water holding characteristics and air space in these materials is good and there is no advantage from mixing any of these basic ingredients with sand, pumice or other materials.

Different liming rates are needed for these two materials:-

Material Dolomite Lime - rate kg/m3 of mix
peat 10
fine ground composted bark 4
Other fertiliser additions are the same for peat or bark, 
Fertiliser Rates- kg/m3 of potting mix
Calcium Nitrate 0.47
Potassium Nitrate 1.27
Superphosphate 4.0
Magnesium sulphate 0.5
Fritted trace elements FTE 36 0.5

Fritted trace elements are the preferred source of trace elements as 
they release nutrients slowly over a long period of time, but cannot be 
leached out of the mix by over watering. An alternative is the Kinsealy 
trace element mixture given below. These chemicals are all water soluble 
and can be leached from the mix by over watering. 

Kinsealy trace element mix:

Fertiliser Rates- grams /m3 of potting mix
Borax 14
Copper sulphate 26
Iron chelate 41
Iron sulphate 41
Manganese sulphate 17
Zinc sulphate 17
Sodium or ammonium molybdate 3

Seed Germinating Mix The above potting mixes are too high in nutrients for ideal conditions for germinating seeds, but a seed sowing mix can easily be prepared by diluting either of the composts with an equal volume of peat or bark.

Liquid feeding These potting composts provide an adequate level of nutrition for about the first 4-5 weeks growth of tomatoes after sowing, but plants will benefit from liquid feeding from about the fourth week after sowing.

Revised 14 May 1997, :R.A.J.White 14 May1997