The majority of home growers have been lead to believe this species should not be watered, or watered infrequently. 
If you are having problems with your plant this article will explain why and the reasons will probably surprise you!

The ZZ plant, Zamioculcas zamiifolia is found in a region of Africa which has somewhat extreme growing conditions.  An unusual aroid (member of the family Araceae) the ZZ grows naturally in eastern Africa primarily in the countries of Zanzibar and Tanzania but the plant is also found in other African countries.  Although it is true those countries have a dry period that condition does not persist year round since there is also a very wet period of heavy rain.  This species suffers in the cold.

An aroid, Zamioculcas zamiifolia (ZAM-e-o-CUL-cas, ZAM-e-eye-FOL-e-a) is a sub-erect herb which sometimes grows to 0.75 meters (2.5 feet) or larger in height.  It is commonly found growing in rocky areas as well as on stone in its native region of the African continent.  Commonly known as the ZZ plant due to its unusual scientific name the plant is one of only a few species that can be regenerated from a single leaf blade (leaflet).  The normal leaflet count is four to eight on each side of the rachis that is their primary support, however in some variations the leaflet count can be substantially higher.

Known by many regional as well as poorly devised common names including Zanzibar Gem, Aroid Palm, Money Tree, Eternity Plant, the Chinese New Year Festive Plant, Succulent Philodendron and Arum Fern the plant is popular around the globe   Zamioculcas zamiifolia is neither a fern, a palm, nor Philodendron but it is in the same plant family as the genus Philodendron which is also a member of the plant family Araceae. 

This species was described to science in 1905.  Some sellers advertise Zamioculcas zamiifolia is a "new plant" but in truth Zamioculcas zamiifolia has been around since the beginning of time.  Commercially, the plant has been sold since the year 2000.   The genus name Zamioculcas was derived due to a vague similarity to the foliage of a group o of Cycads  found in the genus Zamia.   The genus Zamia is in the family Zamiaceae which contains fern-like plants native to tropical and subtropical America while the ZZ plant is in the family Araceae.   Despite the general appearance there is no scientific relationship between Zamioculcas zamiifolia and plants in the genus Zamia and it is not a fern.

Like much of the misleading plant information found on the internet it is commonly believed the ZZ plant is found in the desert but aroid scientific texts state clearly there is only one aroid species found in desert terrain anywhere in the world, and it is not Zamioculcas zamiifolia.  That information can be confirmed  in the text The Genera of Araceae on page 46, "No Araceae occur in true deserts except Eminium spiculatum subsp. negeuense, from the Negev desert (Koach 1988)."   Later in the same paragraph you can read, "Zamioculcas zamiifolia is a succulent plant which stores water in its thick petioles and is sometimes  found in very dry habitats, but is more common in evergreen seasonal forests and savannas."  The Negev is both a desert and semi-desert found in southern Israel.

The same misleading information attempts to tell you this plant does not need to be watered regularly which is completely in conflict with the normal growth information known by science regarding the species.  I recently tried repeatedly to explain this to a plant forum discussion group interested in learning why some of their plants were dropping leaves but every single member appeared to refuse to accept any of the science or scientific reasoning why those leaves were falling from the plant.  There is a scientific cause,

The Genera of Araceae continues by stating the distribution of the single known species of Zamioculcas is tropical east and subtropical southeast Africa including Kenya, Malawi, Mozambique, South Africa (Natal), Tanzania including Pemba, , Zanzibar, and Zimbabwe.  It further states the ecology of the plant is "tropical moist forest, savannas; geophytes on forest floor or in stony ground, forest floor or in stony ground". Please note this scientific text clearly states the plant is found in "tropical east and subtropical southeast Africa" as well as "tropical moist forest" and other locations. Does that not make anyone wonder why the plant is commonly sold as an arid dry species that does not need water? In both tropical and subtropical forests it rains!

An invalid claim that appears to have originated out of SE Asis in the summer of 2010 now claims Zamioculcas zamiifolia can cause cancer!  Internet discussion groups include the bogus notion the ZZ plant is so poisonous a clay pot cannot be used for another plant once it holds the ZZ since the "pot can be dangerous to touch".  Such rumors are based on reading untrue information on another website and then, as happens with all rumors, enhancing and elaborating on it repeatedly, and posting an enhanced notion on another website again and again.  These stories have been spread for years on the internet about aroids but no scientific foundation can be found.  This quote came from retired research chemist and aroid expert Ted Held, "Just a quick check on Google ("Zamioculcas" and "poison") did not find anything substantive. As far as I can tell, this appears to be hysteria."  Noted aroid botanist Peter Boyce in Malaysia responded, "The best one circulating here in Malaysia is that the pollen alone is enough to cause death in adult humans. I know of NO science whatsoever to back-up these claims."

If you believe the plant is dangerous because it contains calcium oxalate crystals you should know that the same chemical substance is found in Parsley, Chives, Cassava, Spinach, Beet leaves, Carrot, Radish, Collards, Bean, Brussels sprouts, Garlic, Lettuce, Watercress, Sweet potato, Turnip, Broccoli, Celery, Eggplant, Cauliflower, Asparagus, Cabbage, Tomato, Pea, Turnip greens, Potato, Onion, Okra, Pepper, Squash, Cucumbers, Corn and other vegetables most of us eat on a daily basis.  It is true some aroids can be very distasteful and may even cause severe pain in the mouth and throat but to claim they are "deadly poisonous" is without merit.  Just because something may taste really bad does not mean it will kill you.  The best possible advice is to simply not put an aroid leaf in your mouth but I assure you aroids are eaten all over the world.  Have you ever been to Hawaii and had Poi?  How about Jamaica, the Caribbean or South America  and dined on Callaloo, Taro, Dasheen, Dalo, Eddo or Potato of the Tropics?  All are Colocasia esculenta, a common aroid developed by the Chinese more than 10,000 years ago as a staple diet.  People eat it all over SE Asia every day!  (click the link to read more)  If you are prone to believe falsely elaborated internet rumors please read this link which provides information based in science:  Calcium oxalate crystals

Zamioculcas zamiifolia is found naturally growing in lowland forests on rocky lightly shaded terrain (infrequently in deep shade) as well as dry grassland.  The species appears to enjoy moderately bright light and commonly becomes deciduous during dormancy.  Becoming deciduous is the natural dropping of the leaves during the dry season.  If you found this site because your plant has begun to drop leaflets the reason is natural.  Your plant is going dormant, likely due to insufficient water.

Once the leaflets begin to drop it is not uncommon for them to form a bulblet or tubercle at the point where the petiole and leaflet join.  The petioles are green with darker blotches that run transversally across the petiole.  These leaflet tubercles allow the regeneration of a new plant.  The tubercles regularly develop at the juncture of a leaflet and petiole.  Despite incorrect found on the internet this species does not grow from a bulb or a corm.  All aroids that have an underground starch storage until only grow from a tuber.  Despite claims on some garden websites, Zamioculcas zamiifolia is not stemless.  Instead, the ZZ or Zee Zee grows from an underground tuber which is the true stem that is also tough and woody.

Since the plant can tolerate long periods without water the internet is filled with half truths about this species that are not scientifically accurate.  Yes, it will survive, but that does not mean it will be comfortable.  Despite the information often offered the plant needs water like any other plant and is more inclined to drop all the leaves if not watered!  During the native dry season Zamioculcas zamiifolia does become totally deciduous and commonly looses all its leaflets while it waits for the rainy season to return.  Those leaflets are then capable of regenerating a new plant.  All plants need water in order to combine with oxygen in order for the chlorophyll to produce sugars to feed the plant.  The oxygen is then returned to the atmosphere for other living organisms to breathe.

The scientific text, The Genera of Araceae states this type of leaflet to plant regeneration is not common under the heading Leaf tubercles and regeneration:  "Tubercles regularly develop at the juncture of leaflet and petiole in Pinellia ternata (Hansen 1881, Linsbauer 1934, Troll 1939), at the apical end of petiole in Typhonium bulbiferum (Sriboonma et al, 1994) and at the first and second order divisions of the leaf of Amorphophallus bulbifer (Troll 1939)- Tubercles in Pinellia may also form spontaneously along the petiole or can be induced in the basal part by cutting into segments (Linsbauer 1934). Tubercles may develop in Typhonium violifolium at the leaf apex, the petiole apex and at the apex of the sheath (Sriboonma et al, 1994)."

"Regeneration of tubers, leaves and roots from leaf segments is well known in Zamioculcas zamiifolia and Gonotapus boivinii (Engler 1881, Schubert 1913, Cutter 1962).  Isolated entire leaflets of Zamioculcas and Gonatopus spontaneously develop a basal swelling, followed by the formation of roots and up to 3 buds, over a 6-9 week period for Zamioculcas.  Leaf regeneration in Gonatopus is more rapid.  The results of experimental manipulation of isolated leaflets grown in culture show that any part of the compound leaf is capable of regeneration".

The parts that appears to be a "leaf" are truly leaflets or a part of a compound leaf.  A compound leaf is composed of a number of leaflets on a common stalk known as a rachis.  Although growers that are family with plants such as a Philodendron would likely call the rachis the "stem", in the case of this species the true stem is underground and grows a stalk-like structure (the rachis) that supports the petioles and individual leaflets.  All the leaflets on a single rachis make up one complete compound leaf.

When the leaflets fall to the ground they attempt to replicate themselves as a natural reproductive process by growing a  tuber which forms naturally at the junction of the petiole and the leaflet but roots may develop from other parts of the leaflet.  The petiole is the stalk that supports the leaf or leaflet while the rachis is complete leaf's support.  Once the rainy season arrives the habitat is no longer dry and the plant has managed to survive by duplicating itself but can grow very well in a wetter growing situation.  Plants that have survived by appearing to be "dead" can then grow new leaflets.

The stem (central axis) of the plant is found underground as a tuber.  The tuber is correctly known as the stem which  supports the rachis that supports the petioles and leaflets.  The petioles are technically a part of a leaf or leaflet and during the wet season both the stem and petiole swell to store water as do other succulents.  Being able to survive without water is a survival characteristic, not a normal growing condition, so the ability to store water in a water retention structure is vital to the long term survival of this species. 

Since tubers (tubercules) can be regenerated at the junction of the leaflet and petiole this is one method from which a new plant can be naturally propagated by a home grower.  This characteristic is limited in the family Araceae (aroids) to Zamioculcas zamiifolia and Gonotopus bovinnii.  A very few other species can be grown from a leaf cutting including some Amorphophallus species as well as one known aquatic aroid.  Though commonly called "stems"  by growers in all plants the petioles are the stalks that support each leaf or leaflet and the petioles should not be called "stems".   This link explains the difference between a stem and a petiole. 

Using this 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 in a a closeable clear salad container with a sandy soil mix also containing a small amount of good soil, Perlite, and bark.  With the adaxial surface (upper side) facing upwards.  Keep the high humidity in the container by covering the leaflets with the lid or clear plastic kept in moderately bright light.  You may just be lucky enough to grow a new plant but be aware the process is not rapid easily taking months!

The majority of websites simply pass along growing ideas promoted by plant sellers which sometimes work to the benefit of the seller, not the house plant grower. Even though many sites incorrectly recommend to rarely water the plant if you read a scientific text written by a botanical expert you will learn the ZZ plant lives in a long period of wet followed by enduring the normal dry season.  Just because a plant can endure a drought does not indicate it prefers a drought.  Recommending to rarely or never water a specimen is very poor advice since the plant needs both a wet season along with a somewhat drier period.  Leaving the plant constantly dry will only result in the eventual loss of the leaves and likely the plant if it is not quickly resuscitated with water.

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 are "following the rules". Those are the same "rules" which advise growers to rarely water the plant.  Quite simply, those "rules" are not correct!   Because some growers don't understand what the term deciduous means house plant growers tend to panic and think their plant is about to die.  Had the plant been watered regularly there is often no reason for the deciduous period to even begin. 

It would at least appear some sellers prefer not to tell customers to expect the plant to drop its leaves if kept dry since you are more likely to just buy a new plant.  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 ability and poor growing growing conditions.  If you starve a plant for water the plant is going to do exactly what Nature designed it to do and go into its survival mode.  Without the water to work with the chlorophyll to produce sugars the plant has no source of natural food.

Some sites including eHow also give very poor advice on how to grow the plant including recommending 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 since the plant grows naturally in fast draining sandy soil. 

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. 

Following Mother Nature's example the soil mixture should be close to that used for cacti and should 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 rachis but as a house plant 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.  Even though nature has designed the species to survive with little water that does not mean it should be purposely dehydrated!  The assumption the ZZ plant should be kept dry year round is a total internet myth and house plant seller's fabrication.

It appears sellers are actually promoting this plant as a house plant because they claim you can forget to water it for long periods of time.  For short periods perhaps, but not indefinitely!   The plant may survive but it will also not prosper and in time will look quite bad just as your cat or dog would look terrible if not fed and watered.  It is likely a very large number of plants are thrown away every year once all the leaflets drop because the grower incorrectly believes it is dead.  In most cases, unless the plant has endured a very long spell without water, it can be easily saved with time and water!

This message came from aroid botanist Peter Boyce who is one of the authors of The Genera of Araceae published by the Royal Botanic Garden Kew in London.  Pete lives and works in Malaysia, "It is a very popular plant, especially with the Chinese, who regard it as lucky (i.e., bringing in money) by the way it can regenerate by the leaflets.   Here we grow it either in pots of red soil (mainly derived from local ultisols of pH 4-5) mixed with 1/5 bulk coarse sand to give a water permeable mix that is high in nutrients, or in the open ground in medium shade. In both 'habitats' plants will receive water virtually every day either from rainfall (Kuching receives ca. 5 m per annum) or in times of no rain then from hand watering. In such conditions plants grow very quickly, producing a new leaf every 3 - 4 weeks.  A plant raised from a single leaflet will carry 12 - 15 leaves and ca. 75 cm tall within a year. The one caveat to giving so much water is that our temperatures are permanently high; minimum 22 C nighttime and 28 C daytime with maxima of 26 C and 36 C respectively. Humidity averages 80%."  Since Pete was quoting temperatures in Celsius it should be noted those temps would be the equivalent of very warm in the United States. 

Despite information on a few websites this species is not a Philodendron.  The genus Philodendron is found only in the Neotropics which include the Caribbean, southern Mexico, as well as Central and South America.   Although Philodendron are grown by individuals all over the world, they are naturally found only in the Neotropics and not in Africa or Asia.  The only relationship between the genus Philodendron (over 1000 species) and the genus  Zamioculcas (containing one species) is both genera are aroids.  The common name "succulent Philodendron" is a very poor choice for a common name! 

Zamioculcas zamiifolia is also not an orchid nor a palm even though at least one website is saying the species is an orchid!  Orchid species produce very distinctive flowers which always contain three petals and three sepals.   Zamioculcas zamiifolia does not produce a "flower".  Instead the ZZ produces an inflorescence with a spathe and spadix.   There are very tiny flowers on the spadix when it is ready to be pollinated, but you would need a magnifying glass to see them.  All the synonym names listed above are now considered to be the same species: Zamioculcas zamiifolia.  They differ only due to natural variation.   Variation is explained later in this article. 

Most Zamioculcas zamiifolia are mass produced for sale.  The majority of specimens sold in discount nurseries are not grown from seed but instead created in a laboratory by a chemical process known as tissue culture (TC or cloning).  The genetic material was extracted from an adult plant, replicated in a laboratory and grown in a lab dish.  Once the plants begin to form they are then grown in multi-chambered trays before being sold to a commercial grower who transfers each plant to an individual pot. 

Since I am also aware that others believe the information on this site is without merit I have elected to reprint the entire text from the scientific text The Genera of Araceae. Please recall that since the original information was written it has been scientifically determined there is only a single species in the genus Zamoculcus:

Zamioculcas Schott, Syn. Aroid. 71 (1856). TYPE: Z loddigesii Schott, nom. illeg. {Caladmm zamiaejbUum Loddiges, Z. zamiifolia (Loddiges) Engler).

HABIT: seasonally dormant or evergreen herb with short, very thick rhizome. LEAVES: few to many, erect, leaflets deciduous during dormancy leaving persistent petiole. PETIOLE: terete, base greatly thickened and succulent, geniculate at apex, sheath ligulate, free almost to the base, very short, inconspicuous. BLADE: pinnatisect, leaflets oblong-elliptic, thickly coriaceous, capable of rooting at base once shed and forming new plants; primary lateral veins of each leaflet pinnate, running into marginal vein, higher order venation reticulate. INFLORESCENCE: 1—2 in each floral sympodium, held at ground level. PEDUNCLE: very short. SPATHE: entirely persistent to fruiting stage, slightly constricted between tube and blade, green without, whitish within, tube convolute, blade longer than tube, expanded and horizontally reflexed at anthesis. SPADIX: sessile, female zone subcylindric, separated from male zone by short constricted zone bearing sterile flowers, male zone cylindric, ellipsoid to clavate, fertile to apex. FLOWERS: unisexual, perigoniate; tepals 4, in two whorls, decussate. MALE FLOWER: tepals subprismatic, apex thickened, stamens 4, free, shorter than tepals, filaments free, oblong, thick, somewhat flattened, anthers introrse, connective slender, thecae ovate-ellipsoid, dehiscing by apical slit, pistillode clavate, equalling tepals. POLLEN: extruded in strands, extended monosulcate to perhaps fully zonate, ellipsoid, large (mean 60 urn.), exine thick, fossulate-foveolate, apertural exine verrucate. STERILE FLOWERS: each consisting of 4 tepals surrounding a clavate pistillode. FEMALE FLOWER: tepals strongly thickened apically, st ami nodes lacking, gynoe-cium equalling tepals, ovary ovoid, 2-locular, ovules 1 per locule, hemianatropous, funicle very short, placenta axile near base of septum, stylar region attenuate, stigma large, disco id-capitate. BERRY: depressed-globose with furrow at septum, 1—2-seeded, surrounded by persistent tepals, white, infructescence ellipsoid. SEED: ellipsoid, test a smooth, brown, raphe conspicuous, embryo large, rich in starch, endosperm nearly absent, present only as a few cell layers at chalazal end.

CHROMOSOMES: 2n = 34.

DISTRIBUTION: 1 sp.; tropical east and subtropical southeast Africa:— Kenya, Malawi, Mozambique, South Africa (Natal), Tanzania (incl. Pemba, Zanzibar), Zimbabwe. ECOLOGY: tropical moist forest, savannas; geophytes on forest floor or in stony ground.