The Oklahoma Garden Planning Guide linked below is a wealth of information and includes when to plant, whether to grow from seed or transplant (or either), plant spacing, etc. You should find the answers to most of your questions there.

If you look at the dates they suggest, most of them are a range of dates, such as "Feb. 10 - Mar. 15". In those cases, the first date is the date to plant in southern parts of Oklahoma, the last date is the date to plant in northern Okalahoma, and folks in between can choose dates somewhere in between the two. Generally, with spring planting, if you cannot plant at precisely the right time, it is safer to plant a week late than a week early because of late cold spells.

Of the vegetables and herbs you have listed, these are the ones I would always start inside as transplants:

tomatoes
peppers
cauliflower
broccoli
cabbage
eggplant

The main advantage to starting from transplants is that you will have an earlier harvest. In some cases, that would be considered only a "convenience", but in our climate, it can be essential for success.

Tomatoes, for example, have a very limited time frame (actually, it is a specific temperature range) during which they bloom and set fruit. If your plants are too small to be blooming at the time that the temperatures are right, you won't get much of a harvest.

With some cool season crops like broccoli, cabbage and cauliflower, it is important to start from transplants so your crops mature before hot weather has an adverse effect on them.

There is truly very little you "can not" sow directly in the garden, but you'll get better results if you start some veggies from transplants.

Onions are in a class all by themselves. Most people start with small onion plants which are sold in bundles in late winter. A few grow their onions from seed. I prefer the bundles of plants. Onions bulb up in response to daylength. Once the day length reaches a certain number of hours, and it varies with different kinds of onions, the onion will bulb up and nothing you do at that point will stop it or slow it down. So, in order to get the maximum harvest (big, round onions), your onion plants need to be as large as possible before daylength induces bulbing. For that reason, you will usually get a better harvest if starting from transplants. Some experienced gardeners do start from seed, but I wouldn't do it until I had a few years of onion-growing experience.

Root crops like carrots, beets, radishes, etc. always do best when direct seeded. They get long so quickly that growing them inside even for a week can mess them up.

When starting seeds inside, it is common to get "spring fever" and start seeds too early. This can result in having plants that are the right age/size to go into the ground long before air and soil temperatures are appropriate. It is very hard to keep fast-growing seedlings inside for very long as they really need instense sunlight and will "stretch" and become leggy (too much stem in comparison to too little leaf) because they need more light than they're getting inside.

For peppers, tomatoes and eggplant, it is best to start their seed no earlier than two months before their outdoor planting date. So, you've started your pepper and tomato seeds a bit early. I am in extreme southern Oklahoma, with a last freeze date of March 27th, and I usually start my tomato and pepper seeds the first week in February and expect to plant them outside no earlier than March 20th and sometimes not until early April. In northeastern Oklahoma, you probably would set out your plants 3-5 weeks after I set mine out in southern OK, unless you have a very warm microclimate. Plants that are held too long inside are slower to take off and grow when transplanted outside, so correct timing can be very important.

To start seeds indoors, you will need bright fluorescent lighting and it doesn't matter how bright and sunny a south-facing window you might have, the sunlight alone will not be enough. You can make a simple light shelf for seed starting with ordinary shop lights hung on a simple assemble-it-yourself shelving unit (metal or plastic) from a home center store or from Wal-Mart. If you hang the lights from the shelves with chains, you can raise and lower the lights as needed. Ordinary fluorescent bulbs work just fine and I wouldn't waste my money on more expensive high-spectrum lights. Young seedlings need to have the lights so close to the plants that the plants almost touch the lights. I like to give my seedlings 16 hours of light and 8 hours of darkness daily, although that is not a formula engraved in stone.

To direct sow, you need for soils to be a certain temperature. Seed that is planted too early simply will not germinate quickly enough and often rots if the ground is wet. So, I keep one eye on the planting dates and the other eye on my soil temperatures and plant when both are in the right range. You can take your own soil temperatures using a standard meat thermometer or you can rely on Oklahoma mesonet station reports for your county's soil temperature. If you are going to be growing in raised beds, you may find that the soil in the raised beds warms up a few days earlier than the ground at grade level.

With some crops, like lettuce or radishes, you can succession sow additional seed every couple of weeks to extend your harvest period.....because there are some crops that do not keep well and you can only eat so much at one time.

With most herbs, I have more-or-less equal success with either direct seeding or starting seed indoors about 5-6 weeks before I intend to transplant the plants outdoors.

Getting all your crops planted at the right time involves a tremendous amount of forethought and planning, and then the weather has to cooperate.....and so do the seeds. Remember that very little of the planting calendar is absolutely, positively engraved in stone and don't beat yourself up if you cannot get everything into the ground at the ideal time. There is no such thing as a "perfect" gardener or garden......there are just too many variables, particularly rainfall and recurring cold spells.

I suggest you look carefully at the planting distances in the garden planning guide and draw out your garden on paper. Figure out the spacing of each row of crops and make sure you have room to grow everything you want to grow, then adjust your plans as space dictates. If you are going to use Square Foot Gardening or other biointensive gardening methods in which closer spacing is used, refer to your book or guide to figure out what is recommended using that method. Drawing it all out on paper is very helpful and it helps you to understand exactly what you have room to grow.

Then, after your plan is made, figure out the transplanting date for each item, and count backwards and figure out how early to start the seeds. For most transplants, I like transplants that are in the 3 to 5 week stage, depending on which kind of vegetable it is. For peppers and eggplants, 6 to 8 weeks is OK. Remember that most seeds will take 7 to 10 days to sprout at the correct temperature, and add that to your planting date.

So, suppose you are going to aim for a tomato transplanting date of April 20th. And, suppose you want to have a 5-week-old plant to set out. Count back 5 weeks from April 20, add 7 to 10 days for seeds to sprout, and that tells you when you should start the seeds inside.

I know this is a lot of info to digest all at once, so....after you've read it and think you understand it, come back and ask us any questions you can think of.

We have a lot of other veggie gardeners here, and we all do things differently, so I am sure you will get lots of good advice from many different people. We all learn from one another!

Dawn

Here is a link that might be useful: Oklahoma Garden Planning Guide