Why a watering range beats a watering schedule
Ask an extension horticulturist how often to water and you will get a question back. Clemson HGIC answers that there is no pat answer: frequency depends on the plant species, its growth stage, its location, the type and size of its pot, the mix and the weather. The University of Illinois Extension is just as blunt: people want a schedule, and it usually does not work. So most care sites give you the drying rule, water when the top inch is dry, and stop there. That is correct, and it leaves you checking pots every day.
Our calculator goes one step further without pretending to know your plant better than you do. It starts from the rule each guide records, gives that rule a reference range of days for a standard situation, then scales it by the factors Clemson and Illinois name. Unglazed terracotta loses water through its walls, so it multiplies the interval by 0.75; low light by 1.45; winter rest by 1.6; a gritty or bark mix shortens it; a pot without drainage lengthens it and cuts the volume to pour. The result is a window of days to start checking, not a date to obey, and it always comes with the finger test and the weight test that settle the question.
What every plant guide contains
Each guide opens with a direct answer of about forty words, then a care card with the same eight facts in the same order: light, water, humidity, temperature, soil, feeding, pets and size. Below that come the watering calculator set to the plant, an introduction you can expand, and sections on light, water, soil and pH, humidity, temperature, fertilizer, repotting with a pot size tool, propagation, common problems in a symptom, cause and remedy table, and pet safety with the ASPCA entry. Questions people ask, related plants and the dated list of sources close the page.
The light section converts each plant's range into foot-candles and lux using the Illinois Extension categories: about 75 for low, 150 for medium, 300 for high and 1,500 for direct sun. Across our guides the preferred light runs from medium light to direct sun, and 17 plants accept low light, from the snake plant to the pothos.
The six drying rules behind the calculator
Every plant on this site carries one of six rules, chosen from what its sources say. Here is the reference range each rule starts from, for a 6-inch plastic pot with a drainage hole, standard mix, bright indirect light, summer and average humidity.
- Keep evenly moist: 3 to 5 days; African violet, Bird's nest fern, Bonsai, Boston fern, Calathea, Fittonia, Gardenia, Hydrangea, Lucky bamboo, Maidenhair fern, Majesty palm, Mint, Polka dot plant, Prayer plant, Venus flytrap
- When the top inch is dry: 5 to 8 days; Amaryllis, Anthurium, Areca palm, Arrowhead plant, Basil, Begonia, Bird of paradise, Chinese evergreen, Christmas cactus, Coleus, Croton, Cyclamen, Dieffenbachia, Dracaena, English ivy, Hibiscus, Jasmine, Money tree, Norfolk Island pine, Olive tree, Oxalis, Parlor palm, Peace lily, Philodendron, Pilea (Chinese money plant), Poinsettia, Rhaphidophora tetrasperma, Rubber plant, Schefflera, Spider plant, Staghorn fern, Tradescantia, Weeping fig
- When the top 2 inches are dry: 7 to 11 days; Alocasia, Cactus, Cast iron plant, Ficus Audrey, Fiddle-leaf fig, Meyer lemon tree, Monstera, Peperomia, Rosemary, Sago palm
- When the top half of the pot is dry: 9 to 14 days; Bromeliads, Hoya, Jade plant, Kalanchoe, Lavender, Monstera adansonii, Pothos, String of bananas, String of pearls
- When the mix is dry all the way down: 14 to 21 days; Air plant, Aloe vera, Burro's tail, Echeveria, Haworthia, Lithops, Ponytail palm, Snake plant, String of hearts, Succulents, Yucca, ZZ plant
- When the bark is nearly dry: 6 to 9 days; Moth orchid
These reference ranges are our model, labeled as such on the methodology page. They are deliberately conservative on the wet side, since a plant left a day too long recovers and a plant drowned for weeks often does not.
Pet safety, checked against the ASPCA
Toxicity on this site always comes from the ASPCA Animal Poison Control Center, which publishes separate lists for cats and dogs. Our pet-safe checker copies both lists, 987 entries, with a script we can rerun at each review, and never adds a verdict of its own: a plant the ASPCA does not list is shown as unknown, not safe. Each plant guide quotes the ASPCA entry, the toxic principle and the clinical signs. Of our 80 plants, 31 are non-toxic to both cats and dogs: African violet, areca palm, basil, Boston fern, bromeliads, burro's tail, cactus, calathea, cast iron plant, Christmas cactus, echeveria, fittonia, haworthia, hibiscus, hoya, jasmine, lithops, majesty palm, money tree, moth orchid, Norfolk Island pine, parlor palm, peperomia, pilea (Chinese money plant), polka dot plant, ponytail palm, prayer plant, rosemary, spider plant, staghorn fern, Venus flytrap.
Common names cause most mistakes. The ASPCA's rubber plant is a Peperomia and its fiddle-leaf is a philodendron, neither of them the Ficus sold under those names. The guides point out each of these traps, and the checker shows the botanical name next to every match so you can compare it with your plant label.
Diagnosing problems from 486 sourced entries
Every guide ends its problems section with a table that pairs a symptom with its cause and a remedy, drawn from the guide's sources. Each row also carries a symptom key and a cause key from fixed lists, which lets the diagnosis tool pool all 486 rows: pick yellow leaves and it counts how many guides blame overwatering, low light or pests, weights your own plant three times, and adjusts for whether the mix is wet or dry. It never invents a cause that no guide records.
Clemson HGIC is the reason the tool starts with care rather than disease: most houseplant problems have environmental or cultural causes, and true diseases are uncommon indoors. Water, light, salts and pests explain nearly everything in the tables.
How the sources are chosen and dated
We accept a short list of sources: the NC State Extension Plant Toolbox, Clemson HGIC, the University of Illinois Extension, UF/IFAS, the University of Minnesota Extension, the Missouri Botanical Garden, the Royal Horticultural Society, and the ASPCA for toxicity. Retailer blogs, forums and encyclopedias are left out, even when they rank higher in search, because a care figure is only as good as the place it comes from.
Every figure in a guide points to the sources it came from, and each source carries the date we read it. When sources disagree, as they do on the minimum temperature for orchids or the pH for monstera, the guide reports the disagreement instead of averaging it away. The editorial policy explains how errors are reported and corrected.
Start here if your plant is struggling
Most rescues follow the same order. Check the mix two inches down: wet for days points to the overwatering guide and, if the roots are brown and soft, to the root rot guide. Then check the light, since stretched stems and small pale leaves mean the plant is starving for it. Only then turn the leaves over and look for webbing, white cotton or tiny flies around the pot, covered in the pests guide. Leaves that yellow from the bottom up, one at a time, may simply be old.