Young avocado tree sprouting from a pit. Photo: herbsathome.co
There are many tropical fruits that can be grown from a seed—oranges, lemons, mangoes, date palms, coffee plants, etc.—but the best known is probably the avocado (Persea americana). Watching its huge pit split in two and sprout a thick, rigidly upright sprout is fascinating. The robust seedling is miles away from the skinny little ones most of our vegetables and annuals produce. Growing an avocado also a great experience to carry out with small children in order to teach them how plants germinate and grow. Plus, you get a free houseplant!
Admittedly, avocados generally make pretty mediocre houseplants, but still, they’re inexpensive to grow and raising one, even if it’s a bit of an ugly duckling, can be fun and informative.
Traditionally you’re supposed to germinate the pit over a glass of water, and if you want to do that, no problem. But the “glass of water” treatment is not mandatory. After all, do you think an avocado pit has to hover in the air over a puddle of water in the wild? Of course not. It germinates in contact with the soil just like any other terrestrial plant. Although far from its native jungle, it will still germinate if you just sow it in potting soil. But sprouting it in water at least offers the advantage that you can better observe the plant’s progress as it germinates: after all, the roots will be visible through the glass. This can be especially interesting as a teaching experience for young children.
Here’s how to start an avocado indoors in both water and soil.
Before You Start
Choose a slightly softened avocado, a sign that it’s fully mature. Extract the pit, then clean and dry it. You can remove brown envelope that surrounds the pit if you want or leave it intact. Whether you do or don’t, the results will be the same.
It’s important to place the pit in the right direction (especially if you’re growing it over water). One extremity will be slightly pointed, like the top of an egg, and should face up. The other will be more flattened, with a paler mark. This is the bottom of the pit and should, of course, face down.
Over a Glass of Water
If you do you want to germinate your avocado pit over a glass of water, press 3 or 4 toothpicks, wooden matches or plastic forks into the pit. Insert them all around the pit, at about mid-height, spacing them evenly. Suspend the pit over a transparent glass or a mason jar. Pour water into the glass until the base of the pit touches the water. Now set the glass in a rather warm spot (68˚F/20˚C or higher), adding water as necessary so that the base always remains in contact with moisture.
After a few weeks, the pit will split vertically and a large root will grow down into the water. Soon after, an upright stem will rise from the top of the pit. Congratulations! You have achieved germination!
Don’t wait too long before transplanting the young plant into a pot: you’ll find it will better tolerate the transition when its roots are just starting to form then when the glass is a mass of tangled roots … and that’s what happens when you leave it dangling too long in a glass of water. Set the pit into the pot, covering the roots with potting mix, so that it is half covered with soil and voila! Your young avocado is up and growing!
In Potting Mix
You’ll save time and effort by sowing the pit directly in a pot of growing mix. Simply fill a 4 inch (10 cm) pot with moist soil up to about to 1/2 inch (2 cm) from the top. A drainage layer of gravel is not necessary nor even recommended; just fill the pot with mix from bottom to top. Next harvest the pit as above, cleaning and drying it, then plant it in the pot, covering in soil to about half its height. Set the pot in a warm place (68˚F/20˚C or more) and wait patiently. With this method, you won’t see the roots appear, but after a few weeks you will see the pit split in half and an upright stem emerge.
Surprise: You have Twins!
Sometimes more than one stem will sprout from the pit: there can be 2, 3 or even 4 or more. That’s because some pits are “polyembryonic”: they produce more than one embryo. In other words, the pit can have twins! This occurs frequently with some clones of avocado. If so, simply let the extra stems grow. This will give you a plant that is naturally a bit bushier than normal.
Up to this point, light was not necessary, but as soon as the stem has appeared, leaves quickly follow and they need light, lots of light. Full sun is not too much for this plant native to the South American tropics, although it can tolerate partial shade.
From now on, treat your little avocado like the houseplant it is. For example, watering it as needed, when the soil feels dry to the touch. Avoid watering with cold water.
In nature, avocado trees grow straight up, not branching until they are quite tall. This is Nature’s way of pushing the plant to quickly grow through overhanging branches to reach the sun above. It’s only once the tree is basking in the sun that it begins to branch.
Potted avocados try to repeat this indoors, heading straight for the ceiling as fast as they can grow, making for a rather thin, not terribly attractive plant. You often have to force them to become denser by pinching them regularly. Pinching simply means removing the tip of the stem, either between your thumb and forefinger or with pruning shears. Once the stem reaches 6 inches (15 cm) tall, pinch the tip a first time, and from then on, every time the stem gains another 6 inches (15 cm), pinch again. This will slow its race for the ceiling and will force the plant to produce branches (although the avocado is very reluctant to branch abundantly), thus ensuring a denser appearance.
After 4 or 5 months of growth, your plant will be due for repotting into a larger pot. After that, repotting every 2 years should suffice. Your avocado plant will have to spend the rest of its life in a pot, unless you live in the tropics, in which case you can plant it outdoors at this point.
During the summer, allow your avocado to spend lots of time outdoors, an experience it will really love … but always acclimatize it gradually before exposing it to full outdoor sun.
The first year a young avocado mostly lives off the reserves contained in its pit. Afterwards, fertilize it like any other houseplant, from spring to early fall, using the fertilizer of your choice at a quarter of the recommended rate.
Avocado foliage tends to suffer from tip burn and brown patches during the winter. These are caused by the dry air in our homes at that season. To counter this, try increasing humidity with a room humidifier.
Mineral salt accumulation (look for the telltale formation of a white or yellowish crust on the inner wall of the pot) can cause similar symptoms. Make a habit of leaching its soil every 3 months to reduce the accumulation. Just take the plant to the sink and let tepid water flow through its soil for a few minutes, allowing excess water to go down the drain. This will remove any mineral buildups in the soil.
To Fruit or Not to Fruit?
Will your avocado bear fruit someday? Probably not. And if it does, even under ideal conditions it can take 7 to 15 years to reach maturity and produce its first greenish flowers. Even then, it is a reluctant self-pollinator. I suggest you simply learn to appreciate the avocado as a foliage plant … and buy your avocados at the nearest market.
Article adapted from one published on February 17, 2015.