I've had my zz plant over a year. I repotted it 2Xs. Last repot was June 2017 & it continued to thrive. About 1 1/2 months ago I noticed the tips on a couple of leaves on one of the younger stems started turning yellow. Now additional tips of leaves on that stem turned yellow AND now the tips of the leaves on another younger stem are turning yellow. There was also a stem that had 1 single leaf ever since I had the plant & it has never grown. To my surprise the entire leaf & stem was yellow but I pulled it before I thought to take this pic.

I have been treating all of my plants with neem oil for 4 months & did notice a couple of leaves turn yellow at least 2 other plants 1-2 days later. In addition I bought a light that shines down on my plants at least 2-3 times a week. I have 1/2" drainage hole in the bottom of the pot. What's happening? The stems are not soft nor did they smell.

1) Poor drainage in the new pot, root rot?
2) Neem oil concentration too high & it being under a light for 10hrs 2-3Xs a week killing it?
3) bug issue?

S.O.S

Hello and welcome! What was the reason you treated all of the plants with Neem oil?

Oops, I just remembered I repotted it 3Xs. The 1st time I repotted it from the cheap black plastic pot that they kept it in at the store.

After being in it's new plastic pot there were tiny little gnats all around it. It looked like an infestation but the plant still looked amazing. The gnats were around some of my other plants too but not infested like ZZ. Still no discoloration, no leaves drying out. I washed the plant off all the way down to the bulbs because I didn't want any larva remaining. I wash out the pot & placed it back in it.

Maybe bugs in the potting soil that I used? Maybe I should have microwaved the soil prior to repotting it the 2nd time?

I repotted it the 3rd time this past June for cosmetic reasons only. It still looked beautifull & even looked like it had a growing spurt but the gnats came back but nothing like it was before. I purchased several plants & placed them next to ZZ.

I did not know anything about plants.Then I read about neem oil & went crazy. I sprayed all of my plants weekly to get rid of the gnats.

1) Over sprayed and/or high concentration levels?
2) Should have quarantined the new plants that may have had different bugs?
3) Microwaved the new potting soil before repotting my plants?
4) Under the lamp for 10hrs 3Xs a week?
5) All of the above?

I can place ZZ in another part of the room for low light, stop spraying as often & at a lower concentration. What I don't want to do is dig it up to check the roots. After 1 1/2ys I noticed the first new sprout & I don't want to disturb it. Afraid it will die.

HELP! I do not know what I should do.

What has your watering been to the plant? How do you water it, how often?

I have been watering it once a week or evey 2 weeks since I had it

Those gnats might be fungus gnats. If they are, then you might have some fungus in your soil. If you're doing any recycling in your home / kitchen, they might be coming from that material. But I don't know that fungus or other gnats would cause that yellow tip thing. Just thought I'd mention it.

I admit I never thought a Zamioculcas would be prone to fungus gnats infestation, since it's not a plant that you would think has high humidity situation around it. Don't fungus gnats thrive on moist soils? If you had been watering once a week, in my opinion it's much for this plant, it thrives on the dry side. Maybe that gave the soil the right conditions fungus gnats need? Just my two cents.

The problem began with your decision to repot and your use of potting soil that apparently was contaminated with fungus gnat larvae. Neem oil has little effect on fungus gnat larvae. Washing away all of the soil to eradicate the gnat larvae did some serious damage to the tiny root hairs that do most of the work. Although that no doubt got rid of the gnat larvae, you introduced a new batch when you used the same contaminated soil. The leaf discoloration is a result of root damage.

That's the explanation. The problem is what to do now. I am reluctant to recommend disturbing the roots further, but it may be necessary. Gently remove the plant from its pot and shake loose any of the soil you used. I hope you will find some healthy roots that have started to grow into the remaining soil. If so, leave that soil intact and move the plant into a pot that is just barely large enough to accommodate the roots and just enough soil to cover them. Use a potting mix of 3 parts peat moss and 1 part perlite.

The small pot and limited amount of porous potting mix will allow the soil to dry out sooner. That will deprive the larvae of the moisture they require and also keep the roots healthier. Water just enough so that the top quarter of the potting mix dries out every 7-10 days. Keep it in a warm sunny location.

If you don't want to repot, then allow the soil to dry halfway deep into the pot before watering very lightly. Don't spray or mist and don't use any neem oil; it is not a cure-all that it is promoted as being.

Always use sterile potting mixes and never use outdoor garden soil.

I have a bag of potting soil at home. I microwaved it to kill the bugs that may have been in it. I should be able to use that, right?

I'm leaning toward to taking out the entire plant to will check the 2 stalks that are affected by root rot. I may not place them back in the pot.I don't want anything to spread. Should I attempt to cut off the root rot or not? I could take those 2 pieces & place them in a separate pot after I cut off the rot & see what happens. I will have to Google a pic of root rot to know what to look for. I will remove any saturated soil & replace it with the microwaved soil. I WILL NOT WATER IT FOR 3 WEEKS!

How's that sound?

I couldn't wait! I think my roots look pretty good. I did not wash off the roots.

You shouldn't be using soil that requires microwaving to sterilize it. Better to use a sterile potting mix from the outset.

Root rot is not usually a disease that spreads. It occurs when the roots are deprived of oxygen typically when the soil is kept too moist for too long.

I wish you had not removed all of the existing potting mix. That said, use a very small pot with a mix of 3 parts peat moss and 1 part perlite rather than whatever microwaved potting soil you have been using. Water it once after inserting the root section and then don't water it again until it is dry about one-third of the way deep into the pot. Water as needed, not by the calendar.

Two new and smallstem and leaves turned yellow .I did cut all the yellow leaves but what shud I do with little yellow stems

@Kiranstheco - Please post a photo of your ZZ Plant, including its pot.