For the first time ever, I think, I washed all my pots and seed trays in the autumn. I got given quite a few and these were washed as well. I only washed them with a strong detergent and warm water so I don't think that there are any unwanted chemicals lingering in the recesses of the trays.
There is some debate about whether washing pots is a necessity. If you are growing seriously then the cleaner and more hygienic you can make your pots, trays and greenhouse the better. As we are usually using sterilized compost nowadays, there is little prospect of infection from the soil. However, there is a possibility of bad bacteria, fungi and viruses building up on unwashed trays, pots and greenhouses. If there is time and I am inclined then I wash pots. It is always best to use a hand brush on dry pots first and only when most of the compost has been brushed off to wash them in soapy water.
Washing the trays removed the problem of bringing dirty, pest infested trays into the house. I could easily justify taking inside the pristine, onion tray, which was also in a transparent plastic bag.
I used a large 23 x 35 cm tray and filled it with New Horizons peat free compost. There is still some doubt whether peat free composts are as good as the peat composts. I find that germination using New Horizons is relatively good especially compared with other peat free composts.
After filling, I tap the side of the tray to make sure that the compost is fairly compacted inside the tray and then use a plant pot to firm the surface. I planted all the onion seed as thinly as possible covering them with a little sieved compost. This was then firmed down with the bottom of a plant pot.
I gave the seed a good watering and left the tray to drain in the greenhouse before placing it into the transparent plastic bag and bringing it into the house. It now sits on a west facing window sill.
Some people suggest that you put seeds in the airing cupboard next to the water tank. If you still have an airing cupboard with a hot water tank, I think that it is too warm in there and seeds germinate and grow so quickly that they usually end up long and drawn out. Not the best start for a plant’s life. Seed usually needs warmth to germinate but after that they become much hardier and can be put into relatively cooler temperatures. I will put mine into the cold greenhouse until they are big enough to transplant and then they will be put into “cell” seed tray inserts. As New Horizons is a multipurpose compost I will use this to transplant as well.