Zinnias are one of my favorite annual flowers. They attract pollinators to my vegetable garden and they make great cut flowers.
They can be started from seed directly in the garden pretty easily. But I have voracious, seedling eating slugs that seem to have a particular fondness for freshly sprouted Zinnia seedlings.
So I hedge my bets and start some Zinnia seeds early so I can put out larger seedlings which the slugs seem not to like nearly as much.
Zinnias do not like to have their roots disturbed and will sulk from transplant shock. So instead of planting these in trays, I use individual peat pellets which can be put right into the soil at planting time. You can buy peat pellets where seeds are sold. They come dry and you just soak them in warm water. They puff up and become like little plugs of seed starting mix held together by netting.
I just plant the seed in the top. Here I put them in a water reservoir from one of my seed starting flats. I divided the pellets by Zinnia variety (I grow several kinds). I can put the clear dome that comes with the seed starting tray over the reservoir to hold in the moisture until the seedlings sprout.
I can bottom water them by adding the water to the reservoir and letting the pellets soak it up. Once the seedlings get a set of true leaves, I add liquid fertilizer to the water at quarter strength (the peat pellets don’t have any nutrition).
They will be a bit bigger and more “slug resistant” when it comes time to plant them outside (for me, that is in mid-April). I just pull off the bit of netting and plant the whole peat pellet – no root disturbance and a happy Zinnia.