You can water at the top or the bottom. Many people get fungal disease, which affects seedling growth, by watering on top of the soil if it is kept too moist. This has never happened to me, but you want to be careful how much water you use. You can avoid this issue by pouring water into the bottom catch tray; the seedlings will absorb it up through the holes in the tray.
When it comes time to remove your seedlings, a butter knife is your best friend. Just insert it gently along the side of the soil and pop your seedling out.
Always be sure to wash and sterilize your tray kits before use for new seeds. The moment after I transplant my seedlings, I wash my trays out and remove any dirt or debris and let them dry out before storage. When it comes time to start new seeds, I soak my trays in a diluted bleach solution to kill off any lingering bacteria that could harm my new seed babies. You can use a 9:1 ratio of water to bleach, or 9 cups of water for every 1 cup of bleach.
I personally do not use a heating mat and do just fine; however, I see plenty of gardeners and, for sure, farmers who use them and have excellent and speedier germination. I don’t feel this is necessary to get started if your space is warm, but it can definitely help.
There is also an option to purchase a dome. I have used domes at times and not used them at times, and in my opinion, they aren’t totally necessary if you have a warm space to start your seeds. If your space is a little cooler, like less than 72 degrees, then a dome can provide extra warmth and humidity for your seeds to germinate.
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