Buying and growing seeds gives you a much larger pool of plant varieties to select from as a home gardener. If you are like me, you'll want to grow plants you can later collect seeds from and replant. You can't do this with most of the veggies you buy at Lowes or Walmart. They are what's called F1-Hybrids (most of the time). Hybrids have their uses. They often make great plants. Sungold tomatoes, for example, are one of my all-time favorites (though I haven't tried a ton of varieties yet. I plan to.). But with hybrids, you can't collect seeds and expect to end up with plants that are "true to type." They'll vary from their parent plant. They're mutts not pure-bred.
Assuming you have some pure-bred seed to plant, the best way to start them is in a light and fluffy type soil. Many plants will actually grow better if never transplanted. With these type plants, your best bet is directly planting the seeds in the ground outdoors when the time is right (usually after last frost for your area but depends on the plant). These type plants are usually fairly hardy seedlings and prime for a late harvest. Pumpkins are just one example. The county extension office for your state will usually tell you right when to directly seed plants for your region. Seed packets will specify what zone your state is in, but usually your town might have a much different climate from another part of the state, so check your county extension office website.
Some plants, you'll desire an early harvest but the plants won't tolerate cold conditions. Tomatoes are a good example of this type plant. This type of plant should be started indoors. The peat-moss pellet green-houses work great on a small scale. They will run you $3-$15 for 10-100 pods. A little pricey for large scale sprouting, but for small scale, it works pretty nicely.
Get your pods nice and wet and allow them to expand. Once they are nice and expanded, soft, and mushy, you can press your seeds in. A pencil works nicely for creating a hole. Some seeds will grow better resting on top of the peat (it helps if it's a little raked up or loose) and others grow better at a depth (1/4", 1", etc..). It depends on the plant. A general rule of thumb though, is to plant the seed twice as deep as the diameter of the seed.
Leave a cover on your store bought or makeshift green house (saran rap, etc..). This will keep the soil moist and the air humid. The plants should sprout within the advertised amount of time with a fairly high success rate (up to 95%) depending on the plant type and seed age. Fresh seeds are better. If you are saving your seed, that's a whole different article. Once the seeds sprout, remove the cover and add light. A well-lit window or lamp will work. The lamp will contribute to warming the soil which will benefit the speedy growth of the plant. Many plants grow best at 75 or 80 degrees which is slightly warmer than most people's homes.
Another important factor, besides loose, soft, fluffy soil and adequate water is temperature. Seeds won't sprout in any temperature, but if you are growing in your home, chances are the temperature is right. Many seeds grow best when the temperature changes from one range (cold) to another range (warm) and will grow much better if chilled first. Depends on the seed, but most standard varieties aren't too fussy and will grow just fine without chilling.
Once the plants are sprouted and have formed their true leaves (they'll look different than the 1st two leaves that sprouted), you can do one of three things:
- Let it develop in the peat pod for a direct transfer outdoors at a later time
- Move it to a newer / bigger container to allow more growing time indoors because it's outgrown it's peat pod and it's too cold outside
- Move it outside. Before you move it outside, though, you'll want to harden your plants for optimal growth and least transplant shock. Your seedlings will no doubt be very tender from being grown in near perfect conditions. When they're tender, they grow fast but die easily
The environment in the garden is virtually guaranteed to be more harsh than the environment within your house. So, harden seedlings firt. Start by taking the plants outdoors on a mild day and placing in indirect sunlight for a few hours (1-2 hours at first). Then start exposing to direct light for short periods of time in the morning or late evening. Then leave outdoors in direct sun for 1/2 day for a couple of days. The entire process should take a minimum of one week. Two weeks wouldn't hurt. Now the plants should be hardened a bit and ready for transplant. It's best to transplant on a cloudy / overcast day (best) or late in the day (second best).
If your plants aren't too large, and the dirt isn't too compacted, your best bet is to move the transplant straight into the soil disturbing the roots as little as possible. If it's compacted, break it up a tiny bit, but be careful because the plants are tender and will go into shock if disturbed too much. The plants might (or might not) survive shock, but it will set them back in growing for a while.
If you want a lower mortality rate among seedlings, then follow these intructions.