Seeds aren’t trash. The best avocado varieties in the world have all come from someone planting a seed. Gwen, Fuerte, Hass, Nabal, Reed, etc. They all came from seeds — seeds that someone allowed to grow.
Maybe you want to try your luck and see if a seed you plant will grow into a tree with great fruit or a strong rootstock, or maybe you just want to discover how an avocado tree develops from the beginning. Any way, here is my experience to help you along.
Where to get avocado seeds?
Almost every avocado you eat has a seed in it that will grow into a tree. A seed from an avocado from your own tree will grow, as will a seed from a store-bought fruit.
Here is a tree that grew from a seed inside a Hass avocado bought at Costco:
A fellow Yard Posts reader grew this tree. The tree is fruitful, and the avocados are delicious.
The lesson is that anyone can hit the jackpot; you don’t need a special source for special seeds.
You do want to be sure to plant a seed that is mature though. Judge this by how the fruit tastes. If the avocado tastes good, then it is mature and so is the seed. You can also judge based on the color of the seedcoat, which will get browner the more mature the seed is.
Do you need to do anything to the seed before you plant it? This is not necessary.
Avocado seeds will grow without any treatment. Under avocado trees you often find seedlings growing out of the leaf litter because a fruit has dropped, rotted on the ground, and then the seed germinated. Here is one such seedling I noticed the other day under my Lamb tree:
That said, seed treatments have been tested, and it has been found that some treatments speed up germination. Peeling off the seedcoat appears to hasten germination, at least in some varieties. (See “Effect of the Removal of Seed Coats on Avocado Seed Germination” by E.R. Eggers.)
Also, if seeds have been stored in refrigeration (which they can be, in order to keep them viable for a month or two), germination will be enhanced if the seeds have their coats removed and parts of the seeds are sliced. (See “The Effects of Pretreatments on Avocado Seed Germination” by Bob Bergh.)
Once, I treated a group of fresh seeds (hadn’t been stored in the fridge) by either slicing off tops or just removing seedcoats, and I found similar germination in all.
So my personal routine these days is to let a seed dry for a couple days so that the seedcoat cracks, then I peel it off partially, and then I plant. This gives me reliable germination.
Where to plant? In water
Most of us who grew up in California germinated avocado seeds in a cup of water using toothpicks at some time in our youth. That method still works in the 21st century.
It also works to start an avocado seed growing in water using something else for suspension. A member of the California Rare Fruit Growers in San Diego County makes these boats for the purpose:
Note that no matter the method, the avocado seed does not need any sunlight in order to start growing. And sunlight that is too intense burns the seed, as shown by the browing of the tops of the seeds in the photo above.
Where to plant? Under a tree
Because avocado seeds don’t need sunlight to germinate, but they do need moisture, I have often started them under large trees. I choose a spot that stays moist via irrigation and stick the seeds about halfway into the dirt and cover the top of the seed with mulch.
You can do this under any kind of tree; it doesn’t need to be an avocado tree. I have most often used a large orange tree in my yard. In fact, I’ve germinated too many avocado seeds under that tree. Many still grow there because I haven’t harvested them.
Where to plant? In a container
More often these days, I start avocado seeds in containers. It takes a bit more attention to start an avocado seed in a container compared to in water or under a tree because you must maintain proper moisture within the container, but the advantage is that you have no need to transplant the seedling as soon.
It is better to use a container that is tall and slender as opposed to short and wide. This is due to how an avocado seed grows. (More on that below.)
Soil or mixes to plant in
What to fill a container with? Lots of mixes work, and individuals and nurseries use different ones with good results. The common characteristic of these mixes is that they are light, airy, and fast draining.
When I germinate avocado seeds in containers these days I use homemade compost. I have germinated avocado seeds in the past in containers filled with dirt taken straight out of my yard. That can work too, but it is trickier to keep the moisture level right.
A mix that you can buy at many garden centers that works well for one of my friends who grows many avocado seeds for rootstock is E.B. Stone’s Cactus and Succulent mix, which contains pumice, aged fir, aged redwood, lava rock, and sand.
Professionals have used different blends over the years. Back in the 1960s when Bob Bergh was planting thousands of avocado seeds at U.C. Riverside for breeding, he wrote that he got good results from a “mix of two parts soil to one part peat moss to one part sand.”
Later, breeders and nurserymen stopped using soil in their mix. “Mixes of 3 parts peat moss to 2 parts perlite or 1/3 peat, 1/3 perlite and 1/3 vermiculite are used,” wrote R.G. Platt of the common mixes used in 1976.
Nowadays, coconut coir is often used instead of peat. For example, Brokaw Nursery of Ventura County uses coconut coir and perlite in which to germinate their avocado seeds for rootstock. (They later add materials once the seeds are up and growing.)
How to plant the seed
Now for the actual planting. First, make sure you orient the seed correctly. The top of the seed is toward the stem; this is where the leaves will come out, and it is sometimes a bit more pointy than the bottom.
The bottom of the seed, farthest from the stem, is where the roots will come out, and that side needs to be in the dirt or soil mix or water.
If planting in a container or ground, you don’t need to entirely cover the seed. You can leave the tip of the seed showing. This helps ensure that the seed has enough air, as it is vulnerable to rotting if totally covered and kept too wet.
Likewise if starting the seed in water: don’t entirely submerge it. Leave the tip out of the water.
No matter where it’s planted, the bottom half of the seed needs to remain moist in order to start growing. The easiest way to accomplish this if starting in the ground or in a container is to start with completely soaked dirt or mix on planting day. From there, add water only as the dirt or mix dries around the seed.
Time to germination
How long until sprouting? This depends on a few factors, the most important of which is temperature. At a temperature in the range of daily highs at 75-80 degrees F, an avocado seed will sprout in around a month. It can be up to grafting size within two months.
When to plant avocado seeds
If daily highs are much cooler than 75 degrees, then germination will be slower. So planting in the spring, summer, or fall is best in terms of giving a seed temperatures in which to sprout the fastest.
If you go into an avocado nursery greenhouse, you notice that it feels warm and humid; it’s usually in the 75-80 degree range.
How avocado seeds start growing
An avocado seed looks like a big nut. It is actually two hemispheres called cotyledons that have a bunch of energy stored like a battery that can power a new plant until the new plant can glean energy on its own.
The two halves of the avocado seed split open and a root emerges from the bottom. You can find this happening inside an avocado fruit if the fruit is very mature.
So the root emerges first, before any leaves. That’s one thing to keep in mind.
Secondly, know that the root is singular, straight, and heads deep as long as it’s allowed. If you have a tall container, then the avocado seed can send that tap root down far. If you have a short container, then the tap root quickly hits the bottom. All is not lost, but the incipient tree is somewhat stunted.
Here are two seeds I germinated, one in a tall container and one in a short container.
Look at how the roots in the short one have already hit bottom (even though the sprout on top has barely emerged):
Tall and slender containers are best, and you won’t find professionals using anything else.
When to transplant avocado seedlings
After the little guy has sprouted, what should you do with it? If it’s in water, then you’ll need to get it into a mix that has some nutrients. If it’s in a container, then you can let it grow until it has outsized its container. When that is depends on how big the container is. Check for roots circling on the bottom and up-pot when you find that.
If it’s in the ground (such as under my orange tree), then you ought to dig it out sooner rather than later, as it becomes harder to avoid damaging roots as they dive deeper and deeper. Avocados are known to be shallow-rooted trees once mature, but when they begin life as a seed they first send roots deep.
Now you’ve grown an avocado tree from the very beginning. Keep it in a pot? Plant it in the ground? Use it as rootstock and graft onto it? Oh, the possibilities.
Below is a tree that I started as a seed from a Gwen avocado planted under my orange tree. I dug out the seedling after it sprouted, potted it up, then grafted a Gwen scion on top. Later, I transplanted it into the ground where it happily grows today.
And here is a video of a seed that sprouted from a compost heap in my mom’s backyard and was allowed to grow in place:
(I’ll soon write a post about growing avocado trees in containers.)
(You might also like to read my post about what kind of avocados you can expect to get from a tree that you grow from seed.)
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