We have bought from lots of places over the years and have a formula that works for us. For simple open-pollinated seeds like peas or beans or that kind of thing, we just buy at a hardware store or mail order place like Johnny's. I have bought from Fedco and believe they are excellent and passionate about seeds. Open-pollinated seeds are hard to mess up so a discount packet at Walmart is fine and almost always organic. Fedco has a great selection of apple tree seedlings and ancient varieties.
Sweet corn is from Harris seeds mail order because almost all sweet corn is a hybrid and that requires research and dedication to the effort. I can also choose varieties that show resistance to common corn diseases and that will save your bacon if disease pops up. They have been excellent of 20 years by me.
You need to buy "treated" sweet corn seed because early disease and bugs will wipe you out before you get started. No organic sweet corn for me unless open pollinated and a late in the year planting.
I also have bought smaller garden seeds and Howden pumpkins from Harris commercially and had exc results.
For tomatoes, I use Burpee for any hybrid. They are cutting edge with crop development and I've used them for decades for new varieties and had great results. I know how to grow tomatoes and last year was a good year but we got 462 lbs of tomatoes off of 11 plants with seed from Burpee. The Totally Tomatoes Catalog seems to give a description of every tomato on earth so a great read. Never bought from them but likely good.
For giant pumpkins it's Vesey Seeds out of Canada. Wow, big pumpkins and can ship from USA for ease.
Baker Creek Heirloom Seeds has an amazing catalog and is highly regarded.
For onions, the only place to buy is Dixondale Farms in Texas. Excellent results, excellent product and perfect onions.
For all gardening, the magic is to keep it weed-free. That will change a ho-hum garden to one the neighbors will take pictures of. Same with fertilizer. Go easy on the N- nitrogen, except for corn, and keep your soil packed with rotting vegetation "tilth" from prior years. Almost no P -phosphorus is needed because it runs off and becomes a groundwater pollutant. You DO need P to start corn.
Seed is the cheapest part of a good garden.
