Determine what your average Latest Date Of Frost is by contacting your local office of your states USDA Cooperative Extesnion Service. Up here the average Latest Date of Frost is May 30, the real Memorial Day, but a bit south around Kalamazoo and Ann Arbor that date is May 15, and in northern Indiana and Ohio that date is May 1. For zone 5 Memorial Day sounds awful late.
Corn Gluten Meal is a pre emergent growth suppressor and just how that works can be found at, http://www.gluten.iastate.edu/ from the people that discovered this property. None of what is listed is anything I would feed to seedlings, although some fish fertilizer or kelp meal might be good.

Does anyone else have advice?

Zone 6 here last freeze date is April 20th and gardeners around here already have all except the okra (its a late summer crop here) on your list already in the ground. All of mine are doing well tho I do have the peppers shielded a bit. May 30th sounds awfully late for a zone 6 resident? The zone 6 heat comes on so fast that we usually try to get a head start to beat it. You might want to double check on that date? Check with local gardeners if all else fails. And I'd sure get going on that lasagna bed so it has time to begin doing its thing well before you plant! ;)

As to the containers - the 16 in. plastic cups or styrofoam coffee cups sold in stack at the grocery store work just fine. Poke some drainage holes in the bottom of them. If they are too tall for your seedlings just trim them down to whatever height you wish.

Any good seedling oriented potting mix (little or no added fert) works fine for transplanting and most all veges don't need any feeding prior to planting in the garden. If you wish to feed, keep it minimal and well diluted. None of the items on your list is appropriate for seedling feeding but in addition to kimmsr's suggestions, consider some very mild and well diluted compost tea. Good luck.

Hey thanks for the tips. I'm located in NorthEast OH (oops zone 5b) and we are known for having frost/snow surprise us. Last year we had a big snow 2 or 3 weeks into May and it did a lot of damage to the trees (cause they had their leaves).

So planting usually doesn't take place until the middle of May.

My cucumbers, zucchini, and okra all sprouted in 2 days. Now (4th day), my tomatoes are sprouting. Only thing that hasn't sprouted yet are my peppers and eggplant.

Tomatos should be started from seed 5 or 6 weeks before being set out. Some start earlier if they plan for large plants (needs more than a floro light can provide). You ideally want 6-8" plants when put into the ground.

Peppers you want to start about 8 weeks before planting outside. Not sure about eggplant or Okra as I don't grow or eat either.

Your cukes and zukes are way too early to have started if you are looking mid to late May for plant out. You want plants that just set their 3rd set of true leaves at plant out time. Any later and explosive root growth begins and being in a small container limits root growth not to mention it's hard to get enough light to them as they grow huge. Starting 3 weeks before plant out date is good. Where I'm a little confused is what to do next. I understand that I should wait until the seedlings produce a "true pair" of leaves and then transplant them into bigger containers. How big? Is 4" big enough? I need to grow these guys until around memorial day before they are planted without the danger of frost. Also I could use some recommendations as to where to get some cheap 4" pots.

I like to use 20 oz. disposable cups from the store. You can also use smaller for the peppers, but the 20 oz cups with a drain hole poked in the bottom have served me well over the years. After I transplant the seedlings into their pots, am I supposed to feed them? What can I feed them with? I have access to horticultural lime (white fine powder), alfalfa meal, bone meal, coffee grounds and corn meal (I bought some a few months ago and left it in the fridge, does it go bad?). Correct me if I'm wrong but I wouldn't want to use corn meal until the seedlings are more developed because it inhibits growth? Anyways how much of what and how (tea or mulch)?

Yes, once true leaves grow the seedling is on it's own and the comfort of the seed is gone. For most veggies it is enough to give any old fert at half strength one time before planting out. Nothing you listed is good for seedlings indoors, but fine outside. For any containerized plant seedling or not a water soluble fertilizer is preferred as it gives nutrients right away and doesn't rely upon natural processes to make the nutrients available. I noticed that you used worm castings in the starting media. That should be enough until they are planted outside. It has had time to start releasing nutrients so you should be just fine. Lastly once again I'm growing zucchini, cucumbers, eggplant, tomatoes, okra and peppers. I will be planting them in a newly created lasagna garden (which I will be creating soon). Is there anything I want to avoid putting in the lasagna garden that could stun their growth or burn them? I will be using straw, leaves, coffee grounds, and 6 month old horse manure.

Sounds good. Keep any eye on leaf coloration though. If it lightens/yellows add some fast acting fertilizer. Lack of Nitrogen *may* be a concern in the first season due to the browns composting. If so add the corn or coffee grounds in greater amounts.

Wow thanks Justaguy2 for the detailed reply!

Follow up questions:

1) Yeah maybe your right about the cukes/zucchini, they are already forming their 1st pair of true leaves. Do you think a 5" container would be adequate enough for their roots until they are planted? If worse comes to worse I could plant them in a bigger container?

As for the lighting I've done some customizations to my lights. I'm overdriving the bulbs using a ballast that is meant for lighting 4 bulbs, rewired to lighting 2 bulbs. Hopefully this and the mylar I'm using will keep them healthy.

2) I'm trying to stay organic and don't want to use chemical liquid fertilizers. I don't really have compost to work with to make a tea. Would a few tbsps of milk in a gallon jug do the trick?

Thanks all again!

Don't put corn meal, alfalfa meal, coffee grounds in a transplant container/cup. It wil mold up and may lead to issues. This stuff works great outdoors, but with delicate seedlings and indoors- the guidelines are different.

I have a small thing of fish fertilizer. I use it at half strength on my babies. I hate to buy stuff, but have found that shortcuts etc. with seedlings can lead to disaster.

In answer to your first question I really don't know how well the vine crops are going to do in any size container for the length of time they will have to be in it before going outside. If it were me I would start over from seed, but who knows?

You have worm casings in the seed starting mix. You don't need anything else for seedling fertilizer until they go outside.

I just bought a digital thermometer and it appears the temps are getting to the 90s. What's the max temp these seedlings should be exposed to? I just wired up some 80mm case fans so hopefully that will lower it some.

Which chemical or nutrient can be use to slow the growth of cauliflower and cabbage seedling in nurseries.

I am interested in this post since I personally experienced some nutritional issues while starting my plants from seed earlier this year. I am actually practicing the "vegan-organic" method of growing which prohibits things like bonemeal and fish emulsion. So, what would be good options for me next year to start a healthier batch of seedlings? Anybody have suggestions other than the fish emulsion? I do have access to compost, so compost tea is an option for me. Is there anything else I could feed them? Also for the compost tea, do you have to sterilize the compost first (I read something that if you're going to use compost in a seed starting mix you should bake it first).

Haldun, anything that would slow the growth of any plant would be antithetical to organic gardening/farming, so i doubt you would get an answer here.
veggieholic, I start seeds in compost and do not have any problem with nutritional issues. I do not add bone meal, use fish emulsions, or see the need for any other nutritional supplement for these seedlings. There is no good reason to bake or "sterilize" compost if you are going to use it to start seedlings. The people that promote that thought process are those "conventional" gardeners that need to be concerned about soil borne diseases because they do not have good, healthy soil that helps greatly in keeping plants healthy and disease free.
If you "sterilized" compost before making tea you would have a "sterilized" compost tea, or really a dead product, one that is useless and a waste of your time, energy, and money.