If you can post a picture that would help, but my guess is too much water. The less light they get the less water they need normally. ZZ's only need water normally about once a month depending on your soil.

The immediate response in my mind as I read the post was 'water it less'.

Yellowing or Browning Leaves in a ZZ (unless they're just a bottom leaf aging naturally), are usually overwatering.

I probably water mine every 3 or 4 weeks right now (in a fast draining mix in plastic pots in bright, indirect light).

This response will be a bit technical but the intent is to explain why your leaves are turning brown and dropping (becoming deciduous). If you disagree please feel free to dispute the information presented which was taken from scientifically accurate material or ignore this post completely.o

The ZZ (Zamioculcas zamiifolia) is found in the African countries of Zanzibar and Tanzania. Although it is commonly believed these are "desert" countries, neither of these countries is totally dry countries. Both have periods of significant rainfall followed by some months of dryness. This species is most commonly found In the It is commonly found growing in rocky areas as well as on stone in evergreen forests.

Likely for reasons of being able to sell the plant as one that does not need water, commercial growers promote this plant as one you can avoid watering for months on end but just like any other plant the ZZ needs water on a regular basis in order to produce chlorophyll to keep the leaves alive. Far too many people underwater the plant then begins to panic if the leaves start drying up and falling. The falling leaves are simply a natural process known as being deciduous. Becoming deciduous is just the process of letting you know it is about to become dormant.
Z. Zamiifolia is found naturally growing in both dry grassland as well as lowland forests on rocky lightly shaded terrain but infrequently in deep shade. The species appears to enjoy moderately bright light and commonly becomes deciduous during dormancy during the natural dry season. The leaves are not true leaves but instead are part of a compound leaf where all the leaflets form a single leaf. Complicated? It really isnt necessary anyone understand this in order to grow the plant.

Once the leaflets begin to drop it is not uncommon for them to form a tubercle also called a bulblet at the juncture of the leaflet and the petiole. Start checking the fallen leaflets; you may be able to grow new plants! These leaf tubercles allow the regeneration of a new plant.
The tubercles regularly develop at where the leaflet and petiole (what most people incorrectly call a "stem" and if you use a magnifying glass you can likely see some. Despite incorrect information found on the internet this species does not grow from a bulb or a corm. The species is a succulent aroid and all aroids that possess underground starch storage until only grow from a tuber.
Many websites offer less than good advice on growing this plant because at least some of the growers actually donÂt care if your plant dies. If it dies or "looks dead" you may well throw it out and buy another one. DonÂt!

If you check garden websites you will read where house plant growers commonly ask why their ZZ plant is "dying" and loosing all the leaves when they believe they are "following the rules". Those are the same "rules" which advise growers to rarely water the plant.

Quite simply, those "rules" are not sceintifically correct! Because they sometimes don't understand what the term deciduous means or the purpose of the process, house plant growers tend to panic and think their plant is about to die. Had the plant been watered regularly there is no reason for the deciduous period to have even begun. In truth the condition is a natural part of the plant's growth and reproductive cycle. The loss of all the leaflets does not indicate a plant is almost dead but simply suffering as a result of a genetic survival characteristic and poor growing conditions. If you starve a plant for water the plant is going to do exactly what Nature designed it to do. In this case, the natural defense is to drop the leaflets since it canÂt produce enough chlorophyll and must go into survival mode.

Some sites including eHow recommend the use of "rich soil". Even though a specimen can survive for an amazingly long period of time in rich soil that holds water that does not mean the plant enjoys the condition in which it is being forced to survive. The information to use rich soil is not based in science. This plant grows naturally in fast draining sandy soil that does not stay soggy. Rich soil eventually suffocates as well as "drowns" a specimen causing the roots to rot due to the growth of saprophytes. A saprophyte is an organism such as a fungus or bacterium that grows on and derives nourishment from dead or decaying organic matter.
When the roots of Zamioculcas zamiifolia are kept in wet soil they cannot easily gather oxygen and thus begin to decay. The end result is rapidly rotting roots and eventually a dead plant. However, all of this can easily be corrected.

Following Mother Nature's example the soil mixture should be close to that found in the native regions where this species grows. Use a potting mix for cacti but it should also contain some soil along with a greater volume of sand, gravel and materials including Perlite that will slowly allow the roots to gather moisture while not being starved for oxygen. The plant should be regularly watered but not allowed to stay wet! In nature the ZZ can survive for long periods only as a naked stem but as a houseplant it certainly won't be attractive without the leaflets. Just as a human or animal can uncomfortably survive for periods of time with no food and water so can the ZZ plant.

Many major botanical gardens actually grow this species in their tropical rain forest sections with more "rain" than any houseplant grower would ever consider. IÂve kept one alive in our artificial rain forest for more than 5 years and we water 5 days a week for 6 minutes at a time. Since our ZZ is in very sandy soil it just does not care and continues to grow. I can give you the names of several botanical gardens and universities that do the same. Growers in Malaysia also commonly grow the species in wet rain forest conditions.

Now, as for growing new plants from the leaflets. Using the plantÂs own unique survival ability, house plant growers may be able to grow their own plant using this unique characteristics by placing a leaf with a petiole (especially one where a tubercle can be seen) in a sandy soil mix as explained above with the adaxial surface (upper side) facing upwards. Keep the sand in a fast food restaurant salad tray with holes punched through the bottom to allow drainage. Keep the high humidity in the container by misting the entirety of the soil and the leaflets and by covering them with the closed lid. Keep the clear plastic in moderately bright light. You may just be lucky enough to grow a new plant but be aware the process is not rapid! The normal process is three to six months but many growers have done it successfully.

Now, please forgive me but since there are some growers on this and other sites that feel my explanations are far too technical, I am promoting plant sales (we sell absolutely nothing), and I am only seeking to make myself appear to be an "expert", please read the information below.

I am in fact an officer of the International Aroid Society but I make no claim to be an expert. I simply study aroids. The information presented above comes largely from the scientific text The Genera of Araceae written by botanists Dr. Simon Mayo, Dr. Josef Bogner and Malaysian botanist Peter C. Boyce.

You will find a great deal more information at the link below if I havenÂt completely worn you out to this point!

Good growing!

Steve

Please read: The author of this post does not claim to be a botanical expert. The quotes and/or sources used are noted solely to provide information from qualified and trained scientific experts. Credits are given to the owners of scientific information since that is considered proper protocol in botany. No attempt is being made to associate this author with these experts as a peer, only an interested grower. Accepted facts in horticulture and botanical science sometimes differ so if the answers or remarks given differ from what you have already accepted to be factually accurate please feel free to dispute the information, ignore this post, or preferably attempt to communicate directly with the botanical sources via the FACEBOOK account http://www.facebook.com/pages/South-Miami-FL/International-Aroid-Society/291094100787 of the International Aroid Society www.Aroid.org The sole goal of this post is to share information.

U shouldve just wrote a book!! Lol good info tho...i anit read all of it...