@Warpig - I'm 64 years old, I would take to heart the advice of
@rockm - he is correct, raising trees from seed is the "nurseryman's phase" of bonsai, and the techniques you would learn have little to do with handling and developing mature bonsai. My goal when I started was to have a tree or two that were nice enough to be entered into shows like the National Bonsai Show in Rochester NY. I wanted mature bonsai. Raising seedlings teaches you very little that applies to exhibition bonsai. Yes, every bonsai at some point came from a seed germinating somewhere.
That said, I assume you have a mixed collection, with some older trees, and raising from seed is just a side project to burn off some excess energy. I would only plant seed of trees that you can not find easily or at all in the bonsai trade. And by not being available, I mean it is a desirable species too. For example, right now you can not find 15 year old or older nursery stock of Pinus rigida, the Pitch Pine, that has been grown for bonsai, where you can find 15 year old Japanese Black pine raised by people such as Telperion Farms and in California.
You are in Ohio, so work with trees that are winter hardy in your area. Pinus rigida, Pinus virginiana, Pinus banksiana, all have good bonsai potential but are not available.
Here is an idea, we all have an ugly wisteria somewhere, that shines only for the 2 weeks it is in bloom, and otherwise is hidden. I saw a kiwi vine grown as bonsai,
Actinidia deliciosa, and in bloom they are nice, and with fruit they are quite nice. Gnarly bark. There is a winter hardy in northern Ohio kiwi relative
Actinidia arguta, sometimes called 'Kiwiberry'. Nice rough bark as it ages, unusual flowers in spring, later than wisteria, but before grapes. And nice clusters of grape size fruit that taste very much like Kiwi, but with smooth skin and slightly sweeter. Seed and or young vines are available, you can propagate by cuttings for plant seed. In 5 to 10 years with a little wire these can be nice pre-bonsai.
You could learn grafting, and graft a nice cultivar of Japanese white pine, P. parviflora, and do low grafts, into the root system of JWP scions onto understock of eastern white pine, P. strobus. The resulting grafted trees would be much more cold tolerant than JWP on JBP understock, and would have a better tolerance of wet midwestern and Lakes States winters. One issue with own root JWP is the roots do not like our wet, heavy snow with regular thaws, winters. You are as likely to loose an own root JWP in winter due to wet roots in winter as you are to other issues in summer. Eastern white pine will survive flooding in late winter if it doesn't last too long into the spring. If you select a nice blue foliage cultivar like 'Pentaphylla Azuma' or 'Cleary's' or any of the other nice ones, you could have a saleable crop.
But seriously, I wish now I had invested more in older stock, closer to exhibition quality than I did. I ended up fooling around with too many sticks in pots for too many years. Keep seedlings a side project that does not monopolize too much of your energy. And make those choices of seedlings count. Don't bother with commonly available stock. Elms - a dime a dozen, maples - equally available. Japanese black pine, 15 minutes on the interweb and $100 to $200 and you can have a nice 10 to 20 year head start over starting with a seedling.
So for a seed project, pick something not available in the bonsai market.
52 here. Bamboo grows really fast...
There is a short chapter in Bonsai Techniques II, by John Naka about creating bamboo bonsai. Naka used one of the ''full size'' bamboo species for this technique. He used black bamboo which can mature to over 30 feet and 2 inch diameter culms. The technique works, I've tried it. I successfully dwarfed one culm of a clump. It is a demanding technique, requiring daily attention during the 2 weeks that a shoot is rapidly elongating. Look it up and you will have an interesting, challenging bonsai to make. Because the attention required was beyond my ability to pay attention to detail, in the long run, I failed, and lost my bamboo planting before I got good photos. But I say enough success to know it is possibly if you have your spring free during the several weeks that bamboo shoots.
