If you plan to plant plants outdoors in mid-May, it is a good idea to sow them in February. This way they will have time to develop well before transplanting. Focus on the climate of your region and adjust the sowing dates according to the onset of heat.
It is better to start sowing from February 15. It is not worth sowing before this time, as seedlings that are too early may overgrow and weaken. In the period from February 15 to 20, it is worth sowing ampelous petunia, pelargonium, verbena, gazania, osteospermum, delphinium, evergreen begonia, eustoma, various types of viola, periwinkle, heliotrope and basil.
Also, by the end of the month, you should sow celery root, as it has a long growth period. If you didn't do it in January, February will be the optimal time to sow, which will allow you to get a good harvest.
Verbena and Chinese carnation can also be sown during February. It is important to provide at least minimal heating in the greenhouse, for example, with an electric fireplace. Insufficient heat can have a bad effect on seedlings, and sowing too early will cause the plants to stretch and become weak.

Proven sowing dates show that seedlings sown in mid-February will be well developed by early May. By May 20, they will have bloomed and be ready for planting in open ground.
As for petunias, they can be sown as early as the end of February, but it is better to wait until the first half of March. If they grow too large, their appearance will deteriorate significantly, and after planting in the flowerbed, they will need more time to recover. To avoid this, take your time with sowing and let the plants develop in the optimal time.