One of my avocado plants got rot rotten two months ago and since then it has spread to all my other avocado plants. I have tried everything I can find online to cure the root rot including adding Perlite to the potting soil; repotting the plants in new soil after cleaning much of the rotted roots; using clay pots for better oxygen penetration; reducing the frequency and the amount of water added every week and adding a 3% hydrogen peroxide solution every time I water the plants. Unfortunately, everything I have done seems to have not helped the plants and I'm out of ideas. I have been growing these avocado plants from seeds for almost a year and it pains me to see them slowly getting devoured by this virulent root rot disease. Any advice on how to deal with this would be much appreciated.

Root rot is not catching. Whatever is happening is being caused by your care. How many times have you repotted? That's very stressful for plants, when there is a lot of root damage and they need recovery time. You should expect them to be wilted and sad until the trees regrow those needed roots.

Perlite does add airiness to soil so it will dry faster. Terracotta pots also allow faster drying. But when you water, water until the soil is saturated and then let it dry to about 2 inches down.

If your peroxide water is sizzling when it hits the soil, you are burning the roots. If its not sizzling, its just water with an added oxygen molecule.

What your trees need is a lot more sun.

I'm also wondering if the symptoms started when you transplanted the seeds into those gallon pots. They look to me like they are planted too deeply, and in spite of the perlite, the soil is staying too wet. The tops of the pits should be above soil.

I've always grown avocados by planting the pits 4 inches down. Seeds should be planted 2x their thickness deep...

If it is originally planted that deep, it would sprout and emerge with stalk tissue appropriate to being underground. But if it is started in water, the stalk is aboveground growth. Then if you bury it there is a risk of it rotting. That's my logic, anyway.

Good logic.

I have repotted all the avocado plants once with new soil, but I don't see any improvements. Because of the root rot, I have limited the amount of water for each plant to 1/4 liter per week. Also, the hydrogen peroxide does not sizzle when I add it to the watering can.

How did you determine that all the plants had root rot?

Can you give us a timeline: how did you sprout them, when did you pot them, when did you re-pot?

How much sun do they get?

The more specific info you give us, the better we can help.

H2O2 won't sizzle when added to water.

I planted the avocado seeds in potting soil last April and it took the seeds almost a month and a half to sprout. About two months ago the leaves on one of the avocado plants started to become brittle and fall off. I did some research online and found out that the problem could be the roots of the plant not getting enough oxygen. So I bought a bag of perlite and added it to the potting soil of the sick avocado plant. Afterward, I decided to add some perlite to all the other pots since I still have plenty leftover. I believe that is how the root rot disease was able to spread to the other plants since I didn't properly clean the hand trowel after the initial use. Three weeks ago I repotted all the plants with new soil and started to use hydrogen peroxide every time I water the plants. I also found many dark brown roots that has fallen off when I repotted the plants. I keep the plants indoors since it is too cold outside, but I do have a plant growing lamp and I normally leave it on for around 13 hours. Please let me if you need any other information, thanks.

It will sizzle at first so if it doesn't, its worn out H2O2 - a bottle of water. Shelf life is only about 6 months.

Your little trees look wilted, a sign of compromised roots, either caused by lack of water or because you killed a lot of roots in the re-pot. Either way, the roots are struggling to support the canopy of the trees.

Roots and canopy work together to feed a plant. If one is not working properly, the other will suffer and vise versa. A quarter liter of water per week is not enough as that amount probably doesn't make it to the bottom of the pot where most of the roots are. Water when the soil is dry 4 or 5 cm down. Water until the soil is saturated then don't water again until the soil is dry 4 - 5 cm down.

They are also light starved. Two compromised systems. Your trees need full sun. Water from the roots and sun on the leaves combine in a chemical process called phtosynthesis, to make the food needed by the trees. You will need to solve both problems before your trees can grow healthy.

The expiration date on the hydrogen peroxide bottle says August 2023, so I assumed it is still usable. The issue with adding more water is that I'm afraid to make the soil too wet and worsen the existing root rot problem. The plants are definitely not getting enough sunlight since it is too cold outside, but I was hoping that the plant-growing lamp would compensate for that.

After you open the bottle, the expiration date expires. If you pour a small amount on an open wound and its sizzles, the Peroxide is still good. The sizzle is the healthy cells in your skin being destroyed by the peroxide reaction. The reaction takes place when the H2O2 is added to water (an open wound has lots of water in it) and happens very fast. When the sizzle stops, the reaction is done and you are adding water plus an extra oxygen molecule to your plants. The peroxide is either destroying roots or adding water, that's it. Stop watering until the trees need water.

All lights are not created equally. A full sun light is rated to 6500k and only the plants directly under the light are getting the full sun.

and sorry for your struggles!

The internet is dangerous, when it shows you a plausible scenario but has't fully accounted for other effects.

Keep in mind- the energy of the plant really come from light driving photosynthesis. There's a reason why we all get taught photosynthesis in school.
The avocados would really like to grow in full outdoor sun- the kind that can burn your skin and make you want sunglasses. That's hard to get near with windowsills and plant lights.And hard for us humans to 'grasp' when we just want enough light to navigate the world.

I'm just seconding/thirding the proposals that low light can be compounding whatever other sub-optimal conditions are there.

"Root rot" is not a communicable "disease". It is a manifestation of improper care. Give them as much light as you possibly can (open the blinds ALL the way), keep them moist, and STOP REPOTTING!! It only damages the roots more and causes more problems.

Avocados are not an easy houseplant once they use up all the energy in the seed, especially if they don't get enough light. The brighter the light, the moister they can be.