Key Lime will come true-to-type from seed and may flower in as little as 2-3 years, with good care. Calamondin, perhaps not available at the grocery but maybe from a friend, can also bear from seed in a couple years. Lemons would take longer, and would likely be too big to grow inside the house before they bore their first flowers and fruit, but you could do that by growing a lemon seedling, then as the plant is approaching the ceiling, take a cutting or air layer from the top and using it to replace your original plant. That way the plant "thinks" it's getting taller, whereas you're actually keeping it shorter than the ceiling height. Oranges and grapefruit could be done the same way, but will take even more years (at least 8 for grapefruit; at least 10 for oranges, and that's under ideal conditions), and you'd likely have to go through at least 2-3 cutting/air layer cycles. Your Clementine seeds may flower in 3-4 years, but again, you may have to propagate from the top and so not end up with the original plant. Almost any other citrus that makes pollen (Tahiti/Bearss lime and navel oranges do not) could be used as a pollen source for it.

Squash seed is often a problem when you're buying seed packets. Often the germination rate is low because they harvest too soon to fulfill their contracts. I have saved seed from 'store bought' squash, but then the other problem can be that the farmer used a hybrid of some sort that won't necesarily breed true. Last season I bought a N. GA. Candy roaster at the farmer's market for $4, ate the squash (delicious) and got a pound of seed from the thing. Lost the plants to Powdery Mildew so bought two more this year and will try again. Having said that, your seed should grow next season if you allow the squash to 'Mature'and dry the seed properly. Butternut will last all winter stored in a cool basement so save one for a few months and then 'harvest' the seed. You'll probably do as well as you would with 'store bought seed' without the expense. All gardens(and farms) are experiments in motion so go for it! This past spring I wanted to try my hand at Garlic and 'Seed Garlic' is upward of $20 a pound so I bought six pounds of Garlic at a Super Wal-mart for $3.89 a pound and planted it. It grew, looked different than the parent (a hybrid) but tastes like garlic and made me happy. Sold some at the Farmer's market ( made a hundred dollars that day) and have six pounds of my own 'seed garlic' to plant in a few weeks. Now that's smart gardening. Let us know how it works next season.

Just happened to come across this post. I'd say 95% of my peppers were grown from store bought fruits. They have been productive and haven't given me much problems except for when I brought them outside from indoor growing. One of my sweet bell peppers is fully loaded, it has 6 or 7 giant fruit on it and 1 of them is starting to turn colour now. Here is a picture of my scotch bonnet also grown from store bought fruit.... Unfortunately I didn't put it in a good location because it's surrounded by green beans and a couple corn plants and fava beans.... The good news is the fava beans are almost ready so they'll be gone within a week, two max.

What will happen if you try to save and propagate propriatary seeds is the seed police will show up and arrest you, the seed police are related to the mattress tag police who are all related to Yahootie... You know him, he's the little guy that lives in your fridge and turns on the lite when you open the door. In all seriousness do save your seeds and try the ones you get with dried peppers I've found a lot of the peppers that I get from the Mexican markets up here are air dried and sprout just fine. I save seeds by air drying them on paper plates. I like to use the closet our water heater is in as it's warmish but not hot and there's good air flow in there due to the venting so I never get mold on the seeds. I'll leave them in there for several weeks so they get good and dry. To store them go and find some paper coin envelopes, they are about 2"x 4" and put your seeds in them, plastic will work but if there's any moisture in the seeds you'll get mold and it will kill them, paper mo betta bro. :) What works great is a good size Mason jar with the wire top and rubber seal, use silaca gel in the bottom and put your clearly marked and dated envelopes in the jar and have Yahootie store them in the bottom back of the fridge right next to that freeze dried something in the tupperware where it's cool and dark. If you can't get the silica gel pour 2 inches of fresh rice in the bottom as it will also absorb the moisture. I've kept seeds this way for years, I had some pepper seeds that were at least ten years old kept this way and had better than 60% germination from them.