Hass avocados need to ripen on tree for 13 months

Q We planted a Hass avocado tree in our backyard about 10 years ago. The tree is now about 15 feet tall and seems very healthy. It produces many large avocados each year, but they do not ripen and soften, no matter how long we leave them on the tree. They remain a dark green color.

We have tried harvesting them and leaving them inside to soften, but they don’t. Putting them in a paper bag with a banana doesn’t help either. We’ve even put them in a 200-degree oven for long periods of time and they don’t soften, thus we are not able to eat them.

Do you know why these avocados do not soften? Did we plant the wrong type of tree?

— Harry May,

Sunnyvale

A To answer your question, I contacted Gary Gragg with Golden Gate Palms in Point Richmond. Gary is well versed in avocados and he thinks you might be harvesting them too early.

The Haas avocado needs about 13 months on the tree to ripen, Gragg said — a long wait, but so worth it. The tree should flower and set fruit in April and May, Gragg said, and while those delicious, tempting avocados will be full sized by October, they won’t be ripe until May or June. The fruit can remain on the tree for another six months.

Gragg said that if you have been waiting the 13 months before harvesting and they still aren’t ripe, you might not have a Hass or the rootstock has taken over the tree and is producing something inedible. In Gragg’s words, you might have a dud tree.

The Hass is a good variety for Northern California, but it’s not the only cold-hardy avocado we can grow here. You could replace the tree with other varieties such as the Bacon, the Big Mup, the Fuerte, the Mexicola or the Mexicola grande.

Q Do avocado trees planted from seed produce fruit? I was told they don’t.

— Randy, Bay Area

A The answer is maybe. Many people who plant from a seed taken from a store-bought avocado never see any fruit, while others report waiting up to 15 years for their first harvest. The main reason for the lack of fruit is a bit complicated and has to do with genetics.

Even if you plant a seed from, say, a Hass avocado, there’s no guarantee you’ll grow a Hass tree. That’s because you don’t know what variety tree might have pollinated the tree that produced your avocado and its seed.

The seed will be a genetic combination of both parents, and the stronger genes could determine what variety of avocado grows. You might get a Hass, or some other avocado or even a new hybrid, which is how the world started eating Hass avocados in the first place.

The Hass is a cultivar developed by Rudolph Hass, a Southern California mail carrier and amateur horticulturist. In 1926, Hass was growing Fuerte avocados, the most popular avocado of the day and was looking to grow more trees by grafting the Fuerte onto rootstock.

He purchased three seeds from a seller who didn’t know the history of the seeds, but as Hass was just going to use them to graft his Fuerte onto, it didn’t much matter. Two of the three didn’t grow vigorously. When the grafts failed to take on the strongest one, Hass considered cutting down the tree, but was talked out of it by an expert grafter.

Eventually, the tree began producing very large and bumpy avocados. At that time, all commercially produced avocados had smooth skin. The Hass avocado was born and now all Hass avocados are produced on grafted trees, not from seeds.

But getting back to your question, because of the uncertainty of what tree you have growing, you can’t be certain you’ll have the right pollinator for it. Most avocados are self-pollinating, but they do better when paired with a suitable tree.

If your tree does produce fruit, you might be disappointed with the size and taste of the fruit. Then again, you might find a jewel.

If you’re really keen on having fresh avocados, you’re better off buying a tree from a nursery. On the other hand, if the seeded tree never produces, at least you’ll have a lovely shade tree.