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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. After that, it covers how to keep your existing collection alive through the darkest month of the year.

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 classified as non-toxic. 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 the ASPCA's published toxicity entries.

Poinsettia (Euphorbia pulcherrima) — Toxic, irritant sap

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." 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 (Hippeastrum hybrids) — Toxic, potentially severe

Amaryllis is a different matter entirely. The holiday "amaryllis" sold in bulb kits is botanically Hippeastrum (NC State Extension); the ASPCA files its entry under Amaryllis spp., and both contain lycorine. 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 × buckleyi) — Non-toxic

The ASPCA's Christmas Cactus entry gives the scientific name Schlumbergera bridgesii, lists Easter Cactus as an additional common name, and classifies the plant as non-toxic to dogs, cats and horses. Kew POWO treats S. bridgesii as a synonym of S. russelliana, one parent of the Christmas cactus hybrid S. × buckleyi (POWO). The ASPCA's plant list adds that "the consumption of any plant material may cause vomiting and gastrointestinal upset for dogs and cats."

A note on names: the "holiday cactus" category sold in stores includes Christmas cactus (Schlumbergera × buckleyi), Thanksgiving cactus (Schlumbergera truncata), and Easter cactus (Rhipsalidopsis gaertneri). Iowa State Extension says, "Most plants sold as “Christmas cactus” are actually Thanksgiving cactus or hybrids." The ASPCA has no separate Thanksgiving Cactus or Easter Cactus entry, and its Christmas Cactus entry does not name S. truncata, S. × buckleyi or R. gaertneri. NC State's Plant Toolbox page for S. truncata tags it "non-toxic for cats" and "non-toxic for dogs." If you're unsure which plant you have, keep it elevated and out of easy reach as a precaution. To tell them apart, see Christmas cactus vs. Thanksgiving cactus.

Mistletoe (Phoradendron spp.) — Toxic

Traditional American Christmas mistletoe is Phoradendron spp. The ASPCA's American mistletoe entry (Phoradendron flavescens) lists it as toxic to dogs, cats and horses. It gives the toxic principles as toxalbumin and pharatoxin viscumin (lectins, phoratoxins), and the clinical signs as vomiting, diarrhea, low blood pressure (rare), difficulty breathing and low heart rate. 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 a different plant. The ASPCA entry above covers Phoradendron flavescens; for other mistletoes, ask your veterinarian or the ASPCA Animal Poison Control Center.

Holly (Ilex spp.) — Toxic

Holly berries and leaves are toxic to cats and dogs. The ASPCA lists holly (Ilex opaca) as toxic to cats and dogs via saponins, causing vomiting, diarrhea, and depression, and rates the leaves and berries as low toxicity (ASPCA Holly entry). The attractive red berries are still 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: the FDA warns that if treatment is delayed by 18 hours or more after ingestion, the cat will generally have irreversible kidney failure.

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, slowly at first, and most tropicals still wait for March's stronger light before growing in earnest.

Most tropical houseplants are in full dormancy by December. Growth is essentially at zero for the majority of species. A monstera that grew steadily in June may produce nothing over the winter. 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 corresponds to the Northern hemisphere's 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 at plant height can be very low. For context, University of Missouri Extension puts low-light plants at 50 to 250 foot-candles and medium-light plants at 250 to 1,000 foot-candles.

By window position:

  • South windows: Unambiguously your most valuable light position. On clear days, a south window in December gets more direct-angle sun per hour of daylight than at any other time of year — the low sun angle means it hits the glass straight-on rather than from overhead. Move your highest-light-demand plants here and leave them.
  • East and west windows: Low-duration morning and afternoon light respectively. Adequate for pothos, heartleaf philodendron, and other low-to-medium light plants. Not enough for orchids, succulents, or plants that needed a south window in summer.
  • North windows: The most light-limited position. Realistic candidates only: ZZ plant, snake plant, cast iron plant, and trailing pothos.

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 12 to 14 hour timer (the range University of Missouri Extension gives as adequate when plants also get some natural light) 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, and soil dries far more slowly than it did in July. 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:

  • Snake plant (Dracaena trifasciata, formerly Sansevieria trifasciata): NC State Extension advises watering only every one to two months in winter. Let the soil dry completely between waterings. This plant will look fine.
  • ZZ plant (Zamioculcas zamiifolia): Let the soil dry out between waterings, as NC State Extension advises. The rhizomes hold water well into the dormant period.
  • Pothos (Epipremnum aureum), heartleaf philodendron (Philodendron hederaceum): Water when the soil is dry to the touch down an inch or so, per Iowa State Extension, and expect long gaps between waterings.
  • Peace lily (Spathiphyllum): Watch for slight wilting as the watering cue rather than a schedule. It will tell you when it's thirsty.
  • Amaryllis (if you have one — in a pet-free household only): Water only when the top 2 inches of soil feel dry, as UMN Extension advises. Overwatering amaryllis bulbs causes rot. After the bloom, reduce water further as the leaves begin to yellow.
  • Christmas cactus (Schlumbergera × buckleyi): Water sparingly. NC State Extension advises reducing watering in mid-September as the buds develop and again after flowering.

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 "a humidity level above 60%" for zebra plant (Calathea zebrina), and a heated December home typically falls well short of that. Iowa State Extension notes that spider mites "prefer dry conditions" and that "increasing humidity can slow population growth."

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

  • Place pebble trays under all humidity-sensitive plants — calathea, prayer plant, peace lily, Boston fern. Check water levels in the trays regularly; they evaporate faster than you'd expect.
  • Run a cool-mist humidifier near your plant collection during daylight hours. This is the most effective intervention for dry winter air.
  • Keep all plants away from heating vents, radiators, and the cold zone near single-pane windows.
  • Group humidity-sensitive species together to benefit from mutual transpiration.

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 notes that spider mites "prefer hot, dusty conditions," and Iowa State Extension notes that they "prefer dry conditions" — which is what a heated December interior provides.

Spider mites are the dominant threat. Signs:

  • Fine silvery stippling on leaf surfaces from cell feeding damage
  • Webbing on leaf undersides and between stems in moderate to heavy infestations
  • Tiny moving specks visible under magnification on leaf undersides
  • General leaf dulling, then yellowing, as the colony expands

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. If you have any doubt, isolate it: UMN Extension advises quarantining new plants and monitoring them for a couple of weeks for pests.

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

  • Audit all holiday plants for pet toxicity: Before placing any holiday plant in your home, confirm its toxicity status for your pets. Amaryllis and mistletoe are serious hazards, and holly is toxic, though the ASPCA rates its leaves and berries as low toxicity. True lilies in cut-flower bouquets are a feline emergency risk. Christmas cactus is safe.
  • Check cut-flower bouquets for lilies: Inspect any floral arrangement before bringing it inside if you have cats. True lilies in a bouquet can be life-threatening to a cat even through minimal contact.
  • Continue spider mite inspections: Frequent inspection of leaf undersides on all plants — especially calathea, pothos, peace lily, and any newly arrived holiday plants.
  • Maintain humidity support: Check pebble tray water levels, keep the humidifier running, and reconfirm that no plants are in direct heating vent airflow.
  • Water conservatively: Check every time before watering.
  • Don't repot anything: No repotting until March at the earliest. Root systems cannot establish in dormancy conditions, and Clemson HGIC advises against repotting dormant plants.
  • Don't fertilize anything: Nothing until new growth emerges in spring — typically March for most tropicals; Illinois Extension puts the fertilizing season between March and September.
  • Run grow lights for critical plants: December is the month grow lights earn their place most clearly.

Plants to focus on this month

Amaryllis (Hippeastrum hybrids) — 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; NC State Extension advises a well-lit, warm spot of 70 to 75°F for growth, and UMN Extension advises watering when the top 2 inches of soil feel dry.

Christmas Cactus (Schlumbergera × buckleyi) — Non-toxic

Christmas cactus is the holiday plant choice for pet households. 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 (NC State Extension recommends night temperatures of 55 to 65°F for flowering), 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 (Dracaena 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. Follow the watering guidance above and otherwise leave it alone. 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 non-toxic per the ASPCA, poinsettia's sap irritates the mouth and stomach, 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 × buckleyi, 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 gives the scientific name Schlumbergera bridgesii, lists Easter Cactus as an additional common name, and classifies the plant as non-toxic to dogs, cats and horses. The ASPCA has no separate Thanksgiving Cactus or Easter Cactus entry; NC State's Plant Toolbox tags S. truncata "non-toxic for cats" and "non-toxic for dogs." If you genuinely cannot identify the plant, 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, around the spring equinox, when days become longer than nights 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 still show no growth well into spring, 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 — American Mistletoe, 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, ASPCA Toxic and Non-Toxic Plants — Holly, NC State — Hippeastrum, NC State — Christmas Cactus (Schlumbergera × buckleyi), NC State Extension — Calathea zebrina, NC State — ZZ Plant, UC IPM — Spider Mites (Tetranychus urticae), Iowa State Extension — How to Care for Houseplants, University of Missouri Extension — Lighting Indoor Houseplants, NC State — Snake Plant, UMN Extension — Amaryllis, UMN Extension — Moving Houseplants Outdoors, Clemson HGIC — Transplanting and Repotting, Illinois Extension — Houseplant Care, Iowa State Extension — Houseplant Insect Pests, ASPCA Animal Poison Control Center