If you want to grow an avocado plant from seed, and you're wondering how to get it to grow, here's a little advice. Look at the situation from the seed's point of view. Avocados, or percea americana, grow in warm climates from Israel and Southern Europe to Mexico and the warmer states of the USA. So not surprisingly, one of the main factors determining germination is temperature.
The ideal temperature for germinating an avocado seed is around 70 degrees Fahrenheit, or roughly 21 degrees Celsius. At this temperature a prepared avocado seed will germinate in around ten days. Although the seed may germinate in colder temperatures, it will take much longer, sometimes as much as five weeks or more.
If you've stored your avocado in the fridge before eating the fruit, you're going to need to give it a little encouragement. It's cold.
Give them a bump start
Try wrapping them in damp paper towels, or even a thin layer of damp cotton wool and placing them in the airing cupboard, or somewhere warm and dark. Check in on them after a week, and if the tap root isn't showing at the base, re-dampen them and check in at ten days and two weeks, by which time you should have some signs of growth and they can either be planted or suspended over water to continue.
The other two things the avocado seed needs to germinate successfully are oxygen and moisture. Although the seed can be planted directly into a light, well-drained soil, many people prefer to start them off suspended over water. This both ensures the seed has plenty of oxygen, and allows you to see how the seed is doing.
Sprouting Over Water
Leave the protective brown case on the pit. If you can, get hold of a hyacinth sprouting glass, with an hourglass shape designed to fill the base with water and sit the bulb in the top, and simply pop your avocado seed in there instead. If you can't get one of those, you can use three of four toothpicks to suspend the pit over the glass. Mature avocado trees often respond to stress caused by damage by flowering, so it's just possible that stabbing the pits with toothpicks could encourage them to germinate.
Leave the pits in a bright warm place, but not in direct sunlight, as the tender shoots can easily suffer from sunburn. Keep the water topped up, and change it periodically to stop it turning foul as the root grow into it. When the roots are around three inches and the stem around two inches, it's time to pot the seedling up.
Planting Avocado Seeds
Choose a good sized pot. A 9” one is ideal, but avocados can be planted in a 6” or even a 12” container. First, place a layer of broken crockery or pebbles in the bottom of the pot, to provide adequate drainage, as the roots of the avocado are prone to wet rot, and a plant that suffers this will rarely recover. Next, add a thin layer of charcoal to prevent the soil fouling, then add a light potting compost, preferably with some perlite or cocoa fibre mixed in. Plant the seed with the base of the oval facing down, and the tip protruding from the soil by about a thumbnail. If you sprouted the seed in water first, fill the pot halfway with compost, then place the root ball in the center an back-fill around it to about a thumbnail from the tip of the pit.
Place the pot on a saucer or dish and water well, until the excess drains out of the pot onto the saucer. When the excess has finished draining, discard the water from the saucer and place the pot in a warm position.
If you're planting the seed, place the pot in a dark warm spot until the first shoots begin to grow. If you sprouted it first, it will need a bright warm spot. In a colder climate, the avocado is best grown as a houseplant, or in a conservatory or greenhouse. In a warmer climate, the plants can be gradually acclimatized to the outdoors.
When the roots are forcing their way through the drainage holes in the pot, it's time to re-pot the plants into a container two sizes bigger than the one they are in, or to plant them out in their final position. Either way, this is best done in mid spring, to reduce the chances of the roots being exposed to frosts, and take advantage of their natural growing season.
To keep your avocados happy, in the early stages, water them well, but not too often. The soil should be dry at the surface, but moist when you stick your thumb in up to the knuckle. When you water, give the plants plenty of water slowly, to give the compost chance to absorb it, and keep watering until the excess drains out of the bottom. Let them drain for an hour or two, then discard the run off.
Give young plants a monthly feed of liquid fertilizer diluted into the water. Once the plants become established, feed them two or three times a year and cover the soil with a leaf mulch. If the leaves start to yellow, one of the main reasons is a lack of iron, so make sure you give them a mineral feed with plenty of iron in it.
Although avocados are not the easiest of plants to nurture to maturity, if you can keep them going long enough, they will reward you with a healthy harvest in time.