Starting your own plants from seed is wreathed in mystery and myth. There are many sources that claim that to successfully grow vegetables from seed you need a degree in botany, years of experience and perfect conditions.
The only part that's true is the part about perfect conditions - however, this is also the only part you have control over.
are designed to stay dormant until the right time; this means that they
won't start to sprout or germinate until they get three things;
moisture, warmth and light.
Some seeds don't require light to germinate, but the young seedlings need it if they are to stay healthy. The worst thing you can do is to get the seeds to germinate (with the other two requirements) and then try to grow them where there isn't enough light.
The intensity of the light is only one factor; the length of the time that they get light is also important - this is called 'photoperiod'. Without both the brightness and the length, the seedlings will stretch for the light, and become spindly and weak.
I always use shallow trays for starting broccoli, cabbage and other greens. If the tray or container is too deep, they won't make very good top growth, but the roots will try to find the bottom of the pot.
This is a problem when you go to transplant them because you'll have to remove over half of the roots - this causes the plant to go into shock, and possibly stunt the growth.
The other reason for using shallow flats is that it uses a lot less soil mix - always use sterilized soil for seeding. It's not worth the heartache of trying to grow them in unpasteurized mix, with all the diseases, weeds and other problems that will come along with it.
I use clear plastic domes to protect the seedlings from mice, and also to create a little micro climate of warmth and consistent moisture.
It prevents the soil from drying out too fast.
It's important to shake off the excess condensation, which can help prevent damping off and other fungal diseases from taking hold.
The domes are only on until the seeds are germinated, then they are replace with...
Don't take the risk of letting mice or other hungry critters take all the fun out of growing your own food. Prevent the damage right at the start by making it as difficult as possible for the vermin. I collect bird cages, and this is the time to use them.
Until the seedlings are big enough to go outside, they are protected under the cages. They get all the light they need, and it's easy to water through, but no mice can get through the bars. Lacking bird cages, upside down plastic flats are another choice - keep in mind that they don't allow the same amount of light in.
Speaking of water, I collect the snowmelt off the green roof that was renovated with compost last year - it's ready to use compost tea.
I fill the watering can and put it in the greenhouse to warm up - there is no point in shocking the seedlings with cold water. Tempered, or warmed up to room temperature is best. Water in the afternoon, so the leaves have a chance to dry off before night fall.