Just keep what you are doing. What zone are you living? If you are getting that amount of growth, gritty won't work. Avocados are quick growers and probably should go outside. If they are growing so well, just do what you are doing unless you are planning to bonsai them. I'm not sure if that is even possible with Avocados.

Jane

AM - The gritty mix WOULD work and work very well, but it really doesn't sound like a good fit for you ...... at least at this time. It's quite a bit more expensive than something like the 5:1:1 mix, which requires no screening (if the bark size is appropriate), and the other considerations you mentioned would need to be resolved. Have you checked into the availability of pine bark where you live? Where DO you live?

Why all the avocados? Are you hoping for fruit?

Al

Nil13: What is something I can look at to learn about pruning / root pruning?

jane_ny : I'm at the very top end of zone 4b, in Vermont. There is no outside for me, I was planning on just keeping them in a big pot(s) because they just keep sprouting on me like crazy and I don't want to kill the poor things.

tapla: how does 5:1:1 mix work? Pine bark would be very easy to acquire, Vermont has a very vibrant logging / mulch industry. Again, avocados just sort of spawned. I had been keeping them to do something with them, but I forgot what that was and by the time I found the pits again, they were plants. Fruit would be nice, but I'm not really expecting much since they are inside.

All of the windows in our apartment are large and face west. In another six weeks or so we will wrap them in clear plastic to keep heat easier in our apartment.

This is a good place to start.

Trees in Containers.

AM - ..... looks like you're new to Houzz - welcome!

The link Nil left (above) goes into some considerable detail about maintaining woody material in pots over the long term. You should find it interesting.

"How does 5:1:1 mix work?" I don't know if you're looking for something like good/ better/ best comparisons, but if you are, it's a very productive soil that's very forgiving. If you want to understand the nuts & bolts of what makes it work so well, you can find out by clicking this link. I honestly believe that understanding how water behaves in soils and what effect it's behavior has on your ability to keep your plant's root systems happy represents the largest step forward a container grower can take at any one time. Soo very often a grower's proficiency is limited more by his soil choice than any other factor. You can't realistically expect to have healthy plants unless the root system is happy. Anyway ............ rather than go into depth here, I routed you through the link. The discussion has been ongoing since 2005, so it's a popular topic.

I doubt you'll get any edible fruit from avocados in Vermont w/o a greenhouse, but there's certainly no reason to stop growing them if you enjoy it. If you are growing your trees because you enjoy the nurturing part, there are a lot of trees you can grow indoors (if you have enough light & warmth) that you can keep small. You also get to enjoy the pruning sessions. I often laugh at myself when I'm involved in the almost surgical pruning of very small plants with a LOT of branch & leaf congestion because I think I must look like a monkey grooming a troop mate.

You'll find a recipe toward the end of the OP I linked to above for the 5:1:1 mix. It will serve as good starting point. If you have questions ...................

Are you taking any courses related to agriculture, horticulture, botany, .....?

Al

Thank you Nil and tapla!

I'm not taking any sort of plant courses at the moment but I've had some experience with outdoor plant growing. I decided to look into the differences more thoroughly a few months ago because I was sure there must be a better way, and there is.

Never keep doing what you're doing; always keep striving to improve your abilities. To accept the status quo is stagnation. Most hobby growers never have a clue there are better ways to grow than simply accepting the limitations of soils that end up more like pudding than a plant medium after a good watering. Simply being exposed to the fact there are alternate growing methods that help you throw off those limitations is very often the seed that eventually bears sweet fruit. Nourishing the seed with purpose and enthusiasm is ultimately what paves the way to a thumb that's all green.

AM, you are in Vermont. Wait until Spring and come back for advice for root pruning. You are doing a great job. Carry your plants over the winter with as much light as you can provide. In Spring you can root prune and put them back in the same size pot. I did that for many years in NY.

Some of my large tropicals, stayed in the same pots for years. I just didn't have space to put them in larger pots. I had Plumerias which I root pruned for over 8 years and they stayed in the same size pots. They were beautiful and bloomed for me even indoors over winter. They are now in the ground after we moved to Florida.

It can be done. You don't have to go broke, or crazy dealing with this. I used regular potting mix with perlite and some wood chips. All my large plants thrived and grew well. Winter is always a challenge, but just watch your watering and light.

Hang on until Spring!

Jane