December is full dormancy month — the lowest light of the year, heating systems running continuously, humidity at its winter floor, and a parade of holiday plants arriving as gifts with widely varying levels of toxicity to cats and dogs. Before anything else, this guide opens with a clear-eyed look at what's actually dangerous and what's merely over-hyped. Then we cover how to keep your existing collection alive through the darkest month of the year.

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Holiday plant safety briefing

Every December, well-meaning gifts and seasonal decorations bring a cluster of plants into homes that don't normally have them. Some are completely safe for pets. Some cause mild GI irritation. Several are genuinely dangerous, and at least one — true lilies (Lilium spp.) appearing in cut-flower bouquets — is life-threatening to cats even in small amounts. This briefing covers each one using verified ASPCA data from this site's plant database.

Poinsettia (Euphorbia pulcherrima) — Mildly toxic

Poinsettia has a reputation for extreme toxicity that is significantly overstated. Per the ASPCA, poinsettia is toxic to cats and dogs via irritant sap, causing mouth and stomach irritation and occasionally vomiting, but is generally "over-rated in toxicity." Serious systemic poisoning from poinsettia ingestion is not well documented. It's still a plant to keep out of reach of pets, particularly curious cats who chew foliage — but a cat that takes a bite of a poinsettia leaf and vomits once is a very different situation from a cat that has ingested amaryllis.

Amaryllis (Amaryllis spp.) — Toxic, potentially severe

Amaryllis is a different matter entirely. Per the ASPCA, amaryllis is toxic to cats and dogs via lycorine and other alkaloids. Clinical signs include vomiting, depression, diarrhea, abdominal pain, hypersalivation, anorexia, and tremors — a systemic toxicity profile substantially more serious than poinsettia. Amaryllis bulb kits are sold everywhere in December for indoor winter blooming, and the plant looks harmless. It isn't. The bulb contains the highest concentration of lycorine. Keep amaryllis entirely out of any home with cats or dogs.

Christmas Cactus (Schlumbergera bridgesii) — Non-toxic

Christmas cactus is the good news in this section. Per the ASPCA, Christmas cactus (Schlumbergera bridgesii) is non-toxic to cats and dogs. It is one of the genuinely safe holiday plants for pet households.

A note on the genus: the "holiday cactus" category sold in stores includes Christmas cactus (Schlumbergera bridgesii), Thanksgiving cactus (Schlumbergera truncata), and Easter cactus (Rhipsalidopsis gaertneri). The ASPCA's Christmas cactus entry covers Schlumbergera bridgesii specifically. The closely related Schlumbergera truncata — often sold under the same "Christmas cactus" common name — is not separately listed by the ASPCA at time of writing, but the genus Schlumbergera is generally treated as non-toxic in veterinary literature. Easter cactus (Rhipsalidopsis gaertneri) is separately listed by the ASPCA as safe among pet-friendly plants. If your "holiday cactus" is a Schlumbergera, you're in good shape. If you're unsure which genus you have, keep it elevated and out of easy reach as a precaution.

Mistletoe (Phoradendron spp.) — Toxic, potentially severe

Traditional American Christmas mistletoe is Phoradendron spp. — and it is significantly more dangerous than poinsettia. Per the ASPCA, mistletoe is toxic to cats and dogs via phoratoxins, viscotoxins, tyramine, phenylpropanolamine, and alkaloids. Clinical signs include vomiting, diarrhea, abdominal pain, difficulty breathing, slow pulse, collapse, and possible death. This is not a decoration to hang at pet height or leave loose where it can fall. If you use real mistletoe as a holiday decoration, secure it well above where any pet can reach it, and do not allow fallen berries or leaves to remain on the floor.

European mistletoe (Viscum album) is related and carries similar toxicity concerns. The ASPCA entry covers Phoradendron specifically, but both genera should be treated as serious hazards.

Holly (Ilex spp.) — Toxic

Holly berries and leaves are toxic to cats and dogs. The ASPCA lists holly (Ilex spp.) as toxic via saponins and other compounds, causing vomiting, diarrhea, lethargy, and head-shaking. Severity is generally moderate, but the attractive red berries are a specific hazard — they're visually interesting to pets and can be ingested in quantity. Decorative holly arrangements should be kept out of reach of cats especially, who are better climbers and more likely to encounter elevated displays.

True Lilies (Lilium spp.) in cut-flower bouquets — LIFE-THREATENING to cats

This is the most important toxicity warning in this guide, and it applies to a plant that most people don't think of as a "holiday plant" at all: true lilies (Lilium spp.) appearing in cut-flower arrangements.

December florist arrangements — holiday bouquets, centerpiece arrangements, gift flowers — frequently include Lilium species: Asiatic lilies, Oriental lilies, Stargazer lilies, Tiger lilies, and others. Per the ASPCA, Easter lily (Lilium longiflorum) is life-threatening to cats specifically. Clinical signs include vomiting, inappetence, lethargy, kidney failure, and death. The toxic principle is unknown, but even small amounts — a few petals, pollen on fur that a cat then grooms off, or water from a vase containing lilies — can cause acute kidney failure in cats.

The ASPCA notes that cats are the only species known to be seriously affected. But for cat owners, this is not a nuanced situation: any cut-flower bouquet containing true lilies (Lilium spp.) is a feline emergency risk. If a bouquet arrives as a gift and you have cats, inspect it before bringing it inside. If you find lilies, either remove them entirely or keep the arrangement in a room the cat cannot access. If your cat has had any contact with a lily — including sniffing the pollen — call a veterinarian or the ASPCA Animal Poison Control Center (888-426-4435) immediately. Time matters with lily toxicity in cats; treatment within six hours of ingestion dramatically improves outcomes.

Note: Day lilies (Hemerocallis spp.) — the common garden variety — are also documented as similarly dangerous to cats, though they're not the same genus as true lilies. If a bouquet contains anything labeled "lily," treat it as a potential Lilium or Hemerocallis until confirmed otherwise.

If your cat has had any contact with a true lily, call your vet or ASPCA Animal Poison Control (888-426-4435) immediately.

What's happening to your plants in December

The December solstice — around December 21 — marks the shortest day of the year in the Northern hemisphere, with day length reaching its minimum. After the solstice, days begin lengthening again, but so gradually that January and February look almost identical to December in practice. The light situation doesn't meaningfully improve until March.

Most tropical houseplants are in full dormancy by December. Growth is essentially at zero for the majority of species. A monstera that pushed a new leaf every two weeks in June may produce nothing from November through February. A ZZ plant or snake plant may not produce a single new shoot all winter. This is correct plant behavior and should not be treated as a problem to fix.

The practical goal for December is to keep existing leaves in good condition and roots healthy through the low-point of the light cycle. Nothing more is expected of the plants, and nothing more should be expected of you as a caretaker. Survival through dormancy without root rot, without pest infestations, and without unnecessary interventions is a successful December.

Southern hemisphere readers: your December is our June — summer solstice, peak growth, maximum light. Invert this entire guide and treat it as a high-growth summer management reference instead.

Light this month

December delivers the weakest indoor light of the year. The sun rises late, sets early, tracks low across the sky, and on overcast days — common across northern latitudes in December — usable indoor light may be under 200 lux at plant height. For context, most tropical houseplants need at least 500-1000 lux for positive energy balance.

By window position:

Grow lights are not optional for many setups in December. If you're running any plant that needs medium or bright indirect light through winter, a full-spectrum LED grow light on a 14-hour timer is the difference between a plant that holds its leaves and one that drops them.

Watering adjustments

December is the month when the interval between waterings stretches longest. With minimal photosynthesis, plants consume almost no water — soil that dried in five days in July may take four or five weeks to dry in December. Overwatering in December causes root rot that may not become visible in leaf symptoms until January or February, by which point the root system may be severely compromised.

The rule: water less than you think necessary, and check before every watering.

By plant type:

For calibrated guidance, see the watering frequency calculator at /care/watering-frequency-calculator.

Humidity

December indoor air — heated continuously, windows sealed — is the driest of the year. NC State Extension recommends qualitatively high humidity for most tropical houseplants, and a heated December home typically falls well short of that. UC IPM identifies low-humidity heated environments as the primary driver of spider mite outbreaks indoors during winter months.

Your humidity setup from November should already be running. If it isn't:

Avoid misting. In December's low light and reduced air circulation, wet leaves dry slowly and can encourage fungal spots on susceptible species.

Pest pressure this month

December pest pressure is driven entirely by low humidity and heat stress, not seasonal pest cycles. UC IPM documents that Tetranychus urticae (two-spotted spider mite) populations peak in warm, dry conditions — the precise conditions of a heated December interior. Iowa State Extension notes that heating systems are a root cause of winter pest pressure on houseplants.

Spider mites are the dominant threat. Signs:

Additionally, any new holiday plant brought into your home in December — a Christmas cactus from a relative, a poinsettia from a store, an amaryllis gift kit — is a potential vector for pests. Inspect new arrivals before placing them near your established collection. Isolate for two weeks if you have any doubt.

Fungus gnats are also possible in December if any plants have been consistently overwatered. Allow topsoil to dry between waterings as the first-line control.

See /care/spider-mites-vs-thrips-vs-whiteflies for identification help.

Tasks for this month

Plants to focus on this month

Amaryllis (Amaryllis spp.) — Toxic. Pet-free households only.

Amaryllis is a beautiful plant and one of the most satisfying December blooms available — a single bulb can produce multiple enormous trumpet-shaped flowers from mid-winter through spring. But per the ASPCA, amaryllis is toxic to cats and dogs via lycorine and other alkaloids. Clinical signs are systemic: vomiting, depression, diarrhea, abdominal pain, hypersalivation, anorexia, and tremors. Do not keep amaryllis in a home with cats or dogs unless you can guarantee the plant is in a completely inaccessible location. The bulb contains the highest alkaloid concentration — keep bulb kits away from pets during planting. Amaryllis blooms in a south window and wants temperatures around 65-75°F. Water when the top inch of soil is dry.

Christmas Cactus (Schlumbergera bridgesii) — Non-toxic

Christmas cactus is the safe holiday plant choice. Per the ASPCA, it is non-toxic to cats and dogs. It blooms in response to the long-night photoperiod of November and December. Keep it in a cool room (55-65°F at night accelerates blooming), reduce watering slightly to let the topsoil dry between waterings, and don't fertilize until spring. In a south or east window it will bloom reliably through the holiday season.

Pothos (Epipremnum aureum)

Pothos remains one of the most reliable December plants for indoor collections — it tolerates low light better than most tropicals and will keep a leaf here and there going even in difficult conditions. Per the ASPCA, pothos is toxic to cats and dogs via insoluble calcium oxalates. In December, reduce watering substantially and keep the plant in an east or south window. See /plants/pothos-care.

Snake Plant (Sansevieria trifasciata)

Snake plant is the quintessential December houseplant — it tolerates low light, dry air, infrequent watering, and neglect better than almost anything else you could keep indoors. I water mine once every five or six weeks in December. It sits in a south window and requires nothing else. Per the ASPCA, snake plant is toxic to cats and dogs via saponins — keep out of reach of pets. See /plants/snake-plant-care.

ZZ Plant (Zamioculcas zamiifolia)

ZZ plant stores water in underground rhizomes and can tolerate the kind of benign neglect that December demands of even attentive plant owners. It genuinely does not need water often in December. Per NC State Plant Toolbox, ZZ plant is toxic to cats and dogs via calcium oxalates. Put it in whatever north or east window you have and leave it alone until March.

What NOT to do this month

Don't bring true lilies into a home with cats. This bears repeating. A cut-flower bouquet with Asiatic, Oriental, Stargazer, or any other Lilium species is a potential cat fatality. If a bouquet arrives and you aren't sure whether it contains true lilies, contact the florist or look up the flowers before placing it anywhere your cat can access.

Don't repot. No exceptions. Plants in full dormancy cannot establish roots in new media. A December repotting stresses the root system at the worst possible time and sets the plant up for a difficult winter.

Don't fertilize. Plants in dormancy cannot use nutrients. Unused fertilizer salts accumulate and damage roots.

Don't overwater. With minimal photosynthesis and slower soil drying, December overwatering is the fastest path to root rot. Check soil before every watering without exception.

Don't place holiday plants near pets without confirming toxicity. The stakes vary enormously: Christmas cactus is safe, poinsettia is mildly irritating, amaryllis and mistletoe are serious hazards, and true lilies are potentially lethal to cats.

Don't panic about zero growth. December is dormancy. Plants that are healthy but not growing are doing exactly what they should be doing. Stable, healthy-looking leaves with no new production is a successful December outcome.

Frequently asked

My cat ate some poinsettia. How worried should I be?

If your cat nibbled a poinsettia leaf and is showing mild mouth irritation or vomited once, the ASPCA data suggests poinsettia toxicity is generally overrated — the irritant sap causes GI upset but not serious systemic toxicity. Monitor for continued vomiting, lethargy, or worsening symptoms. If symptoms persist or are more severe than expected, call your vet or the ASPCA Animal Poison Control Center (888-426-4435). This answer changes dramatically for amaryllis, mistletoe, or true lilies — if a cat has ingested any of those, call immediately without waiting to observe symptoms.

What's the difference between Christmas cactus, Thanksgiving cactus, and Easter cactus?

All three are popular "holiday cactus" plants sold in stores. Christmas cactus is Schlumbergera bridgesii, Thanksgiving cactus (more commonly sold as "Christmas cactus" by mid-November) is Schlumbergera truncata, and Easter cactus is Rhipsalidopsis gaertneri. The ASPCA's Christmas cactus entry covers Schlumbergera bridgesii specifically as non-toxic. Schlumbergera truncata is not separately listed by the ASPCA but is treated as non-toxic in general veterinary literature. Easter cactus (Rhipsalidopsis gaertneri) appears on the ASPCA's pet-safe plant list as non-toxic. For practical purposes: if your holiday cactus is a Schlumbergera (flat, scalloped leaf segments), it is widely regarded as non-toxic. If you genuinely cannot identify the genus, keep it elevated out of easy reach.

When will my plants start growing again?

Most tropical houseplants in Northern hemisphere homes begin showing new growth in March, after the spring equinox brings day length back above 12 hours and light intensity starts to recover. A few fast-movers — pothos, heartleaf philodendron — may push a leaf in February if they're in a good south or east window. Most species will wait until March. ZZ plants and snake plants are typically the last to resume growth, sometimes not pushing new shoots until April. If your plants are still not growing by mid-April, investigate light levels and soil conditions before assuming something is wrong.

Sources: ASPCA Toxic and Non-Toxic Plants — Poinsettia, ASPCA Toxic and Non-Toxic Plants — Amaryllis, ASPCA Toxic and Non-Toxic Plants — Christmas Cactus, ASPCA Toxic and Non-Toxic Plants — Mistletoe / Phoradendron, ASPCA Toxic and Non-Toxic Plants — Easter Lily (Lilium longiflorum), ASPCA Toxic and Non-Toxic Plants — Golden Pothos, ASPCA Toxic and Non-Toxic Plants — Snake Plant, NC State Extension Plant Toolbox, NC State — ZZ Plant, UC IPM — Spider Mites (Tetranychus urticae), Iowa State Extension — Houseplant Pest Management, ASPCA Animal Poison Control Center