I have, for some time, sown seeds in a windowsill propagator and potted the seedlings on into plastic drinking cups. This has been quite handy as the plant’s name can be written on the cup itself, saving the use of plant markers. I give away excess plants so I leave it to their adoptive parents to provide the trimmings. The drinking cups are white and not too thick so you can see the roots when they are ready for the next move. Usually the seeds will germinate in almost anything, so I start them off in coir, which has added nutrients and they won’t go hungry whilst waiting patiently for me to move them on.
The plastic cups are small so don’t use up too much compost but when the plants are ready, with a healthy root system, they can easily be moved to a bigger pot without disturbance. I put the drinking cup and plant into the new compost, to the depth required to mould the shape, then take the plant out carefully and fit into the perfectly made hole.
Sometimes however, I don’t have time to deal with so many plants and having grown tomatoes in a hydroponic tank using cubes of rock wool, I have decided to use the seedling cubes as a trial. After soaking the cubes, it’s just a case of dropping a seed into the hole in the cube and wait for it to grow. Some I will put in the Kratky method jars, it’s just a case of popping the cube with the seedling into the net cup, add a few clay balls to steady it and leave it to get on with it. Other cubes can just be potted on to wherever is best for them.
Unfortunately it is a more expensive way of sowing seed and I prefer to find inexpensive alternatives if I can. So my expense this time is put down to experimental interest. I have had success with Perlite and hydrogen peroxide in a polythene food bag but that’s not quite what I’m looking for. The Perlite is still loose and the little seedling roots can’t be transferred anywhere without taking them out the Perlite.
I set up the first seeds in the rock wool cubes just over a week ago and it didn’t take long for them to sprout. Some seeds sprouted faster than others but even in the tray at the bottom of the photo, there are signs of seeds sprouting after only three days. The seedlings in pots were sown in the windowsill propagator and potted into little plastic cups. They seem quite happy in the gravel tray which I keep watered. Most of the plants grow healthily sitting in the gravel tray, it’s heated at the moment because we have sub-zero temperatures at night, but within a day or two, the heating will get switched off. The greenhouse is hot during the day.
Putting the seeds into the rock wool cubes is like dropping them into meringues, its soft, fluffy texture offers no resistance to little roots when they want to reach out to feed.