The first stage in hydroponic tomato growing is to germinate the tomato seeds. I use 3.5cm (1 1/2″) starter cubes. These are first soaked in a weak nutrient solution for a few hours. I tend to use my own nutrient solution or make use of purchased brands such as Formulex.
Once the cubes have been soaked they can be put back in the plastic tray they are supplied in. The tray can be placed in a propagator.
The starter cubes should have a small hole ready to drop a tomato seed in. These holes are often covered over as the cubes are handled. To make sure the hole is deep enough to take a seed I use a large screw to remake the hole. Push the screw about 15mm (3/4″) into the cube. If you grow a number of different varieties of tomato use coloured marker pens to identify different tomato varieties.
I tend to purchase the tomato varieties I want to grow from a seed supplier as I tend to experiment each year. Tomato seeds cost around $3 for a packet. Specialist and hybrid varieties may have only 6 or 8 seeds in a packet whilst established varieties have 100 seeds or more. If you grow the same types each year then you can avoid the expense of buying by producing your own seeds using last years tomatoes.
Once you have dropped a seed into each of the starter cubes then they can be placed in a propagator. I prefer a heated propogator as at 24 degrees Centigrade the germination is quicker. An unheated one will work if the air temperature is consistently above 15 degrees Centigrade – it just takes longer. Initially the propagator should be in a darkened room or covered to block out the light. Make sure that the starter cube is kept moist with nutrient solution and does not dry out. After around 3 to 4 days (heated) or 7 to 8 days (unheated) the seedlings should start to appear.
Once the seedling is visible it should be transferred to a separate propagator which is exposed to artificial light. I tend to keep my seedlings like this until they are 2-3 weeks old. Again the cube needs to be kept moist with nutrient solution. I use the lights for 18 hours and then allow 6 hours of darkness.
After about 3 weeks under lights the seedlings are ready to move onto the next stage – 75mm cubes. The seedlings show here have been placed on their sides so they grow at a 90 degrees angle. This is supposed to help with root development.
The design of the the larger 75mm rockwool cubes means there is a pre-cut hole in them to take the starter cube. First the larger cube is soaked in nutrient solution and then the starter cube is inserted into it.
Once the seedlings have reached a reasonable size they are ready to move into growing slabs (see separate blog post) and the next stage of hydroponic tomato growing can start.