Hi, and welcome. Someone suggested I use this para. in similar situations, so here you are - I would first advise you to do some reading, so you get an idea what it's all about, and don't end up getting something home with no idea how to keep it alive - bonsai are not house plants and in fact, the majority are grown outdoors, where they do better, but if you have no outdoor place to grow things, then you can grow tropicals, which are often grown with supplementary lighting, humidity, etc. Bonsai is a lifelong learning 'hobby' (to most of us, it becomes an obsession very quickly), but as you need to know at least the basic horticultural requirements, and how to choose appropriate trees for your environment, it's important to start by reading (many books available, plus www.bonsai4me.com, www.bonsaihunk.us/cultural.html (for tropicals), and www.evergreengardenworks.com), all of which give good overviews on bonsai in general, and info. on growing specific trees. A really good intro for you would be a local club/assoc., so you get to see hands-on what it's about (there is a lot involved re pruning roots, various ways to shape the tree, why it's important to know in which season to do what work for which tree, how to 'compose' various soil mixes, and maybe most important - how to water (sounds silly til you understand what it entails and how important it is to get it right). Every tree has diff. requirements and every environment is different in various aspects, so find out first if in fact you really would want to get started on the journey, but stay far away from little pots in big stores sold as 'Bonsai' - most of which are just cuttings of larger trees stuffed into little pots with one-size-fits-all care tags [useless!] stuck on them, and imported from overseas in huge truckloads, with pebbles glued(!) to the soil that then need removal, and sold in bad soil destined to discourage you after the trees die of root rot if not repotted into the right stuff. Patience is the first thing you need and if you don't have it, you won't get far, but if you do, you can have an awful lot of rewarding time learning to take care of your little trees (did you know bonsai can be as large as 4' tall and wide?). PS - the trees only end up being 'miniature', but start out as 'regular' trees, not some odd 'special' type of plants. They're more often cut down from larger ones, rather than grown up into 'bonsai', so as to keep the illusion of age with a fat (and well tapered) trunk, but new batches of smaller branches and leaves, and bonsai pots are often not used until the trees are ready for display, sometimes being 'grown out' in the ground for years - the fastest way to achieve good trunk girth. To (finally!) answer your question - every tree grows at a different rate, but you'll learn which are which along the way, but you'll also find that a good place to start is a local nursery (if not supermkt for tropicals) rather than a place that sells 'Bonsai'.

And another thing :-) - don't go digging up anything now, let alone cutting roots or whatever. It's important that you understand first about which trees to dig in what season, depending on where you live, plus what to do with them directly after digging and from then on. It's definitely harder to keep a 'dug' tree alive than one in a pot unless you know what you're doing.