Amalo, what type of soil did you use? Is it well-draining? Perhaps, it's too heavy, therefore staying wet. If possible, add Perlite..
Are you still seeing fungus gnats? If there are gnats or eggs, you will find them on new plant, too.
Don't overpot..Place in a well-vented spot w/fresh air. Toni

I wouldn't have potted the old one with the new one, especially with old soil still on it. The fungus/bacteria that caused the rot are still in the soil. You risk transferring them to your new plant and starting the rot cycle all over again.

ZZ plants are very slow growers and do well with neglect.(i.e. little water). This plant needs to dry out completely before watering it again. ZZ's are succulent plants which grow from a tuber that stores water. As Toni said they need very well aerated, light soil. You can accomplish this with adding LOTS of perlite to your regular mix(if it is a heavy one). I would also add that you should use clay pots, especially for this plant. Clay is porous and allows airflow to the plant's root system which is vital to the plants health. Although, I detest Miracle Gro soils and the like. They're way too heavy and stay wet for too long. Generally, I use Pro-Mix and add perlite to it. Sometimes I use pro-mix with Orchid mix and perlite added or just orchid mix with perlite added, depending upon the plants.

Thanks for your replies. I don't really know if the soil is light but the pot is clay but glazed. It does seems to drain well. I repotted both old and new plant last night, I guess it's too late to repot them and split them. Well I guess I will just have to keep them and see how they go. If the soil completely dries out will the fungus gnats die? What measures can I take? Can I leave the plant a few days outside in the sun? Would it be bad to remove it from the pot and spread the soil and let it dry on the balcony? Sorry for asking so many stupid questions but I am a newbie at this. Thanks in advance

Thanks Tonio. I did repot the plant in new soil but what i am worried about is that the old plant had the old soil on its roots. I can't bake that lol... Can I remove the plant and place in a tray with the soil on the balcony to dry? I can put it in the shade with no sun or rain. Would the plant die if i leave it a few hours without it being covered in soil?

Hi Amalo. If it were my plant, and decided to place soil on the balcony..this is what I'd do..remove soil, place on newspaper or tray..spread out. Leave out as long as it takes to dry (completely.)
Then, run water over ZZ plants & roots..rid as much soil as possible..The zz should be fine left outside of soil (a few hours)
BTW, there are products sold to rid fungus gnats, but since I don't use chemicals, I can't name any..Perhaps someone here has an answer.
Also, I can't remember who posted, but a few ppl mentioned using non-insecticidals to rid gnats..If anyone has an answer, could you please step forward, lol, to help Amalo..Thanks,
BTW, Amalo, if this works, in the future be careful watering plant..Like Growhappy stated, this plant thrives on neglect..Toni

Thank you so much Tonio. I will do that.

Would those yellow sticky traps be of any help? I use them in the summer and they work very well, just a thought.

Eileen

Eileen, great point..I've used yellow sticky traps for aphids, and man oh man did they kill those suckers..It'd be an interesting experiment to see if they worked on gnats..If they did, that would solve many ppl's dilemmas. Non-chemical, fairly inexpensive, and can be home made..Thanks Toni

Sorry, not aphids, duh, white fly..Toni

I've found the yellow sticky cards not useful for killing fungus gnats---they just aren't that attracted to them, unlike whitefly. I also gave up the cards cuz I would have my house all clean and beautifully decorated with my favorite plants, and then see dead bugs stuck to bright yellow cards everywhere. ICK ICK ICK!

My ZZ plant really suffers from gnats too because there is a lot of dirt available around the stems. My favorite product is Gnatrol----it is a naturally occuring bacteria that is only harmful to the gnats. You'll probably have to get it off the internet cuz I've never seen it in stores. It's not expensive---maybe $25 dollars per liter, which will last a LONG time. You mix a small bit of it with water and then just wet down the top inch of soil (do not actually water the plant with it---you'll rot the ZZ and waste the Gnatrol). When you first put it on it'll smell like a ....a bad fart (excuse the language, but that's what my husband thought I was doing in the growing room when I used it---I almost died laughing!). Once it dries there will be no odor at all. :) Happy gnat killing, as I hate those disgusting little buggers. ;)

Oh, one more thing. An inch of fine sand on top of your soil will prevent gants too, but it makes it harder to test moisture levels. Personally it's too much mess for me but I know others who successfully use that technique.

Shiver, why not unpot your ZZ and place in a smaller container since it has much available room?
Oh the Grantrol sounds like it smells, 'wonderful' LOL..that's funny about your husband..
I agree placing anything on top of soil makes it harder to check soil. Even the colorful sands, in various colors and pretty, would have the same effect..Toni

My ZZ plant is pretty large (3.5 feet tall from top of soil to tip), and it has a big root system. No way can I get it in a smaller pot! ;) I have to keep it humid in my home due to resperatory problems---add to that 100+ plants, and even with fast-draing soil you have *gnat heaven*. Gnatrol is my friend---fart smells and all!

I have used the yellow sticky cards to help get rid of a gnat infestation. If you lay them flat instead of hanging them, you will trap many of the adult gnats while you are waiting for the soil treatments to kill the larvae.

Once you get the problem under control, make sure not to leave standing water around, and keep your plants on the dry side. That should keep the gnats under control - until you bring home more plants which probably are hiding the little buggers somewhere in their soil!

Is it just me, or are there more fungas gnats around, seems like since it got warmer, I have more of them, they are driving me crazy too. I have the yellow sticky traps, they are so gawdy, and they havent been doing much for me, I use Safers, that isnt doing much either, I have been looking for gnatrol, but like someone said, its hard to find in the store, I am ready to go full blown insecticide if I cant get them under control soon.....I dont care how anthing smells, I just want them gone.

On another bad note, I picked up my croton today and a few leaves fell off,for no "obvious" reason.....well upon further examination, it had spider mites......all I saw was webbing and miniscule little white things crawling in the web, well that was enough for me, and it went in the garbage......isnt Safers supposed to help with mites??

Tracy

PS if anyone can recommend an insecticide that will work, please let me know, I am up for chemicals, anything, I just need these gnats to DIE!!

Here is where I buy my gnatrol---I've ordered from this place many times and they've given me good service so far.

http://www.gtghydroponics.com/store/0-0-476.htm

I see they say to use 6 applications of it, but I just use it at a slightly higher concentration and it works in about 2 apps for me. I couldn't live without the stuff. :)

A word on spider mites---I have had serious battles with these buggers and what I can tell you is that chemicals do not work. Many others here will disagree with that statement, but that is what my personal experiences has been. I now have two action plans for mites:

1. Plants instantly go in the garbage so as not to let them spread.

2. Take cuttings of the plant, soak them in bleach water (1:10) for 2-3 hours, then root them normally. Many garden webers disagree with my approach and think bleach is too harsh, but I don't think it's any harsher than miticides, and it works better.

I guess that's my 2 cents...sorry if it's off topic.

Shiver, gnats or not, your ZZ plant looks great..glossy green, and so symetrical. Can't ask for more..Toni

You have to be very careful about overwatering the ZZ plant. They can go one or even two months with no water. They have a tuber like structure at the base, it looks like a potato that stores water. They will rot if over watered. Let them go bone dry.

Here is a link that might be useful: ZZ Plant Care

What about a “soilless” medium like a gritty mix? That way no gnats. I made a batch for my Fiddle Leaf Figs and (many) succulents. Would this work for my ZZ’s?

This thread was last active ten years ago. I dont think these people are still active.