Every plant seed consists of a hard shell that protects a sleeping plant with itty-bitty leaves and a root, and enough water and food to tide the plant over until it reaches its destination-- your garden. Think sci-fi, space traveler, suspended animation.
Three conditions trigger or inhibit seed growth: water, soil temperature, and air temperature. If you live in southern Denton County instead of the Garden of Eden you will have to line up favorable conditions to germinate seeds. The local good news is that you can mess up then get a second chance because we have two growing seasons-- a fact that discombobulates immigrant Yankee gardeners.
Second growing season garden starts have to be ready to go in the garden as soon as the daytime temperatures drop back into 90s in mid-September, the last average heat wave date. Seeds require 6-8 weeks between planting and maturity, so you want to sow for fall crops during the first half of July. Keeping the seeds and seedlings wet is as easy as plenty of organic content in your potting soil, and proximity to a hose, but controlling the soil and air temperature requires some creativity.
To start, dump a bag of potting soil in the wheelbarrow, and give it a good soaking. The planting “medium” should be wet when you fill the germination pots. (To protect your manicure use gloves.)
I germinate in 2-3” square or diameter pots so I don’t have to transplant until the starts go into the garden. Sow 4-5 seeds at the recommended depth in a 2-3” container of potting soil. Blanket a little soil over the seeds; give the pots a good misting then park them in dappled sunlight. This can be under loose woven porch furniture, trees, or even bigger plants. I’ve seen people install cheap thin beach umbrellas. The only limit here is your imagination. The object is to control evaporation and soil and air temperature when the world is on the proverbial tanning bed.
The surface of the potting soil should always feel damp, which means a good soaking once every 24 hours most days. The soil in the pot should be wet top to bottom. Don’t mulch little seedlings.
Oh, and a word to the wise: there is such a thing as too much water. If you put the pots to swim in a tray of water, empty the tray when the surface dirt in the pots feels wet. If your seedlings/starts turn yellow they’re overdosing on water. Maybe you can save them, maybe you can’t.
After the seeds germinate pull out all but one. We envision farms overflowing with plants, but the average suburban gardener, for example, doesn’t need 144 tomato starts, just a half a dozen. Plant 6 pots of tomato seeds then cull the growth to 6 plants.