Last spring, I grew petunias from seed for the first time and was very pleased with the results. They can be a bit tricky to germinate so I thought it might be helpful if I shared some tips to help other gardeners that would also like to give it a go.
I sowed the following varieties, which I purchased from the Egmont Seeds Commercial Catalogue (available from the company upon request as it is different to the home gardeners catalogue on their website).
As temperatures in spring can be very temperamental and drop dramatically at night, plus the fact that petunia seeds require warmth to germinate, I highly recommend using a heat pad. If you don’t have one, you can always try using your hot water cupboard.
I highly recommend using 198 or 230 multi cell seedling trays for germinating petunia seeds in as the seeds are small and it helps the plants to form a plug once they grow, making it easier to repot them. I try and sow one seed in each cell so the plants don’t get cramped later on, making it difficult separate the roots. Petunia seeds are often pelleted, making them easier to handle. Do not cover the seeds with seed raising mix, which is what you would ordinarily do when sowing most other seeds. Instead, cover the seeds lightly with vermiculite and water well. I use a spray bottle to mist my seedlings. As it gets warmer, you might need to do this twice a day to prevent the seeds from drying out.
Once your seedlings germinate and grow a bit, you can move the tray(s) to your greenhouse. If you don’t have one, you could try using a cold frame or another protected environment. When the seedlings are large enough, they can be carefully pricked out and repotted into a 60 or 72 cell seedling tray, which has larger cells making it suitable for the next stage of growth.
Once your seedlings have grown and it is warm enough, they are ready to be planted outside. Don’t forget to harden off your plants first by gradually exposing them to outdoor temperatures otherwise they might end up shocked and die if there is no transition period between a warm and protected greenhouse and the great outdoors. You can plant petunias in the ground but I prefer growing mine in containers. For the first time last summer I planted our petunias in terracotta pots and they performed really well, as you can see in the pictures.