Starting seeds inside is a lot easier than you may think! Get the environment right, make a plan, and you will see success! At the end I have included some questions to ask yourself to help you make decisions on your set up and plans.
There are many reasons why your would want to do this:
If you live in a place with a short season it can allow you to grow crops that need a longer time until harvest, like hot peppers and squash plants. It can also allow your plants to produce longer and thus getting a bigger harvest!
Staging of planting can make it so you don't have 100 plants ready to harvest at once. Start portion of the crop indoors, then in 2-3 weeks start a few more. That way when they reach maturity it is at different times. Then, when harvesting you have to consider where you are going to store it and whether or not you can use it, can it, or sell it before it goes rotten. So staging it so that you harvest a smaller quantity at a time may help you if you are tight on space. Lettuces have quick harvest times so you can stage many plantings throughout the spring.
A few things you need to know when setting up:
You want to make sure that the temperature is right for each specific variety of plant. Here is a chart that shows you what seeds like what temps! You can find many versions of these all over the internet or in books. Depending on the company you bought the seed from they also may have a growing guide of general information about that variety.
Split seeds with different needs into different trays/containers so that you can put them in different areas! If tomatoes like it hot and kale likes it cold, you are not going to want those seeds in the same tray.
The actual setup:
There are hundreds of methods for starting seeds that work great. When choosing the container size, always consider that if it is bigger, you may loose the seed or it can easily become overwatered. If the container is smaller, it may need to be transplanted sooner and may dry out quicker. When choosing the medium (soil, paper towel, hydroponic clay pellets, etc.) consider the control of pH and how quickly it will dry out. Soil buffers the pH naturally, but will dry out the slowest, especially in a big container. It also should contain very low levels of nutrients because you don't want to burn the seedlings with too much fertilizer. In hydroponics you control the pH and depending on your system, may not need watering by hand at all.
Consider how many plants you are starting and what lighting they are going to get. In my experience, lighting is everything for getting good roots and plant structure. I use T5 fluorescent lights that are designed for optimum plant growth. I bought them from HTG Suppl, click here to check out the fixture I use. It covers about 2' by 4'. I have tried to use stronger lights and they cook my plants, it gets too hot and I have to water too frequently. To weak of lighting and you will get long and spindly growth as well as weak stems and roots.
We already talked about temperature. Now think about the humidity in the spring time. It's pretty wet outside! So the more you can keep the humidity up during and a bit after germination of seeds, the better success you will have. You do want to be careful of mold because it thrives in humidity, if you see mold the best thing to spray is a diluted hydrogen peroxide.
When it comes to water timing, remember that the seed needs both oxygen and water to allow a root to grow nicely. You don't want the seed to stay wet for too many days, but you also want to make sure to water it when it becomes too dry. The seedling is the most tender stage the plant is in, so it needs to be babied until it has more resistance to stresses.
Questions to ask yourself when starting seeds indoors and planning a garden:
What do I want to grow?
How often do I want to tend to my plants?
Do I want to grow plants in soil or hydroponically?
How much room will I need indoors when the plants start to grow up?
How much space is in my garden and what spacing am I going to use between different plants?
How much do I want to harvest and when? Do I want staged harvests?
How much can I handle harvesting at once?
Am I willing to research and learn what I need to do when I have issues?
How much do I want to invest in my garden? Time, money, energy?
I hope this helps you in your garden journey! Remember that you reap what you sow, but there is a lot of work in between the sowing and the reaping.