Avocados are a rain forest plant. They've evolved to survive as seedlings under a canopy of leaves which blocks out the light. How do they manage? By putting all their energy in to growing as tall as possible as quickly as possible to reach the light. Result - a tall, spindly plant with a long thin stem and a cluster of large leaves at the top. Not desperately attractive as a houseplant or balcony plant. I've had them before and, quite honestly, they ended up looking dreadful.
But I thought I'd see that I'd try again and see if I could keep them lower and bushier. How ? First of all by making sure they have plenty of light, so they don't feel the need to become ganglier than necessary. But I've started off two pots, and they're each going to get slightly different treatment.
Pot number one (top photo) contains seeds that were started off at different times - the tallest went in at the beginning of the summer, the last one yesterday. Starting from now with the two tallest, I shall pinch out the growing tips to encourage them to spread. And I shall start pinching when each one is slightly smaller than the one ahead of it. That way I'm hoping to get bushy growth at different levels - the lower ones masking the spindly trunks of those which are taller. Well, that's the theory...
Pot number two has three seeds. They've just gone in, and as they grow I shall braid the trunks just as you often see done with Ficus benjamin. I'm hoping they'll eventually fuse together (as Ficus benjamin does). But in any case, the effect should be less height (because each trunk has been wound around the others), an apparently thicker "single" central trunk, and a mass of leaves on top. Again, that's the theory. While I can find plenty of advice on growing avocados on the web, and also plenty of advice on braiding other trees, no-one seems to have thought of putting the two together. Or perhaps they have and it just doesn't work. We shall see ...
If you want to grow them, use a fresh seed - plant it almost as soon as you eat the fruit. Let the brown outer coat dry and peel it off. Then just pop the seed into some fertile soil, broad side down and with its nose just showing above the soil level. Keep the seeds moist (not soggy) and wait. Forget all that stuff about sticking toothpicks into them and suspending them over water - would you like toothpicks pushed into your tenderer parts? Just plant them in the pots and keep them warm - I've seen around 20°C (70°F) recommended, but mine have zoomed up this year in temps of around 27°-35°C (77°-90°F). They are rainforest plants, after all.
Then you need to be be patient. It will seem for the first month or so that nothing's happening. Not true - they're developing long thick roots. This is one that I pulled up yesterday because after waiting for weeks and just seeing it get drier and harder, I did decide it had died. But you can see that a long root had already formed before it gave up.
So wait. And then, sometime in the second month, you'll see that the top of the seed has split, and very soon the stem and the first leaves will be poking through. And growing at a rate of knots. Keep them moist (but again, never waterlogged) and feed regularly with a fertiliser containing balanced nitrogen, phosphorus and potassium and also zinc.
Size can also be controlled by trimming the roots annually and keeping them in a small pot, but the size of the leaves means that they're not really suitable for bonsai treatment. Huge leaves on a tiny tree would just look daft. There are dwarf varieties, but I don't think you're likely to find them in your local supermarket.
Avocados are not hardy. Once the temperature drops below 7°C (45°F) they need to come inside - which may become a problem if they do get really big. Cold may also kill the seeds too, so don't store the fruit in the fridge before you plant.
But then, you wouldn't be silly enough to put fruit in the fridge and destroy all the vitamins anyway, would you? And avocado has lots - it contains vitamins A, some of the B group, C and E and is also full of minerals : it has three times more potassium than a banana, weight for weight, as well as calcium, iron, magnesium and phosphorus. And despite it's high fat content, it's mostly mono-unsaturated fats and is low in cholesterol. (1) What more do you want?
Sadly, though, the only avocados you get to eat as a result of growing them may be the ones you buy in order to get the seeds. Sources differ as to how long it takes a tree grown from seed to bear fruit - around ten years seems to be the average estimate (2), but some websites put it at as long as twenty. Don't think our local supermarket need feel too threatened ...