Disclosure: Amazon links on this page are affiliate links, so this site may earn a commission at no extra cost to you. Commissions don’t decide which products are recommended. See the full affiliate disclosure.

May is the houseplant equivalent of pressing the accelerator. Day length is close to its annual maximum, light intensity through south and west windows is genuinely strong, and the tropicals that spent winter in a kind of suspended animation are now pushing out new leaves faster than you can keep up. The challenge this month isn't getting plants to grow — it's managing everything that comes with that growth: stronger light requiring repositioning, higher water demand, and a pest spectrum that goes from dormant-season narrow to full-summer wide almost overnight.

What's happening to your plants in May

May sits at or near the houseplant growth peak for Northern hemisphere growers. The spring equinox was around March 20, and by May day length is approaching the June solstice maximum. Longer photoperiods signal plants to push vegetative growth hard.

Physiologically, tropical species like calathea, alocasia, pothos, and monstera that slow their metabolism through the low-light winter months are now running close to full photosynthetic capacity. Roots are active, stomata are opening and closing rhythmically across a proper day-night cycle, and the growth you see in new leaf unfurling is supported by genuine metabolic activity rather than just stored energy.

This matters for how you care for them. A calathea pushing a new leaf in May is doing something fundamentally different from a calathea in January that looks technically alive but isn't doing much. The May plant actually needs the water, nutrients, and humidity you give it. The January plant needed much less.

Southern hemisphere readers: your May corresponds to the Northern hemisphere's November — these growth notes apply to your spring months instead, roughly October through December.

Light this month

May light is serious light. The sun's arc is high in the sky, days are long, and south- and west-facing windows are receiving direct sun for substantial portions of the day. This is good for most plants — but it creates real problems for tropicals that evolved under forest canopy.

May is the month to move things backward. Plants that sat comfortably near a south window in March can get scorched leaf tips if they stay there in May.

What to do by window direction:

  • South windows: Any tropical that can't tolerate direct sun needs to move back from the window, or you need a sheer curtain. Calathea, alocasia, peace lily, and ferns will scorch. Pothos and philodendron can handle indirect light from a south window at distance.
  • East windows: Morning sun in May is warm but not brutal — a great spot for most tropicals. Spider plants, pothos, and heartleaf philodendron thrive here.
  • West windows: Afternoon sun gets intense. Peace lilies and calatheas need some protection. Monstera can handle it with some protection from direct afternoon rays.
  • North windows: Still the lowest-light option, but May north light is meaningfully stronger than January north light. Low-light workhorses like ZZ plant and snake plant are perfectly content here.

One practical check: if you can see a distinct shadow cast by the plant itself from direct sun coming through the glass, that's direct light, not indirect. Shift accordingly.

Watering adjustments

May watering should increase noticeably compared to what you were doing in January and February. Active growth means higher transpiration, roots are pulling water from the soil, and warmer indoor temperatures accelerate evaporation from the pot surface and soil.

Check before you water rather than following a rigid schedule: push a finger into the soil. Iowa State Extension advises watering when it is dry to the touch down an inch or so; if it's still damp, wait.

Specific adjustments by plant type:

  • Pothos and heartleaf philodendron: Water when the top inch or so of soil is dry, per the Iowa State Extension rule above.
  • Calathea and alocasia: These like consistently moist (not wet) soil per NC State Extension. Check often and water before the soil goes completely dry.
  • ZZ plant and snake plant: Still let these dry out more fully between waterings even in May. Their rhizomes and thick leaves store water.
  • Peace lily: Drooping slightly is fine as a watering signal — it perks up quickly when watered.

The watering frequency calculator on this site can help you dial in schedule by pot size, soil type, and environment if you want more precision.

Do not let May enthusiasm lead to overwatering. The fastest way to kill a plant in peak growth is to keep the soil saturated — you create anaerobic conditions at the roots and fungus gnats follow shortly after.

Humidity

May humidity is more variable than any other month. In many climates, May outdoor humidity is moderate — comfortable, not extreme. But if you've turned on AC early (a common move in warmer climates when temperatures spike before summer officially arrives), your indoor humidity can drop sharply. AC removes moisture from the air as part of its cooling process.

NC State Extension recommends "a humidity level above 60%" for zebra plant (Calathea zebrina), a typical humid-understory calathea. Without a hygrometer, watch the plants for signals: brown, crispy leaf edges on calathea in May are almost always a humidity problem, not a watering problem.

Practical options if your AC is already running:

  • Group plants together. As plants transpire, they raise the humidity in the immediate microclimate around each other. A cluster of calatheas and ferns does better than isolated specimens spread around a dry room.
  • Pebble trays with water. Set pots on trays filled with pebbles and water. As the water evaporates, it raises local humidity. Keep the bottom of the pot above the water line to avoid root rot.
  • A small humidifier near moisture-loving species. If you have calathea, alocasia, or ferns, a small ultrasonic humidifier directed at them makes a visible difference.

Misting is often recommended but the benefit is short-lived: per Iowa State Extension, misting does not raise humidity for more than a few minutes. It can also promote fungal issues on leaves if you mist into poor air circulation. Don't rely on it as a humidity strategy.

Pest pressure this month

May opens the full pest season. You're no longer dealing just with the winter's fungus gnats and spider mites — thrips arrive with the new growth flushes, and if you have AC running and humidity low, spider mites get a foothold quickly.

Thrips are the primary pest to watch for in May. They emerge with tender new growth and feed on young cells, leaving silvery, stippled, or distorted leaves. Check the undersides of new leaves on calathea, alocasia, and pothos — that's where thrips congregate first. Compare what you're seeing to the diagnostic guide at /care/spider-mites-vs-thrips-vs-whiteflies if you're unsure.

Spider mites may seem counterintuitive in a warm month, but they thrive in hot, dry conditions. If your AC is running and indoor humidity is low, spider mites can establish on the undersides of leaves quickly; UC IPM notes that a generation can be completed in less than a week when temperature and food supplies are favorable. Fine webbing between leaves and stems is the giveaway.

Fungus gnats carry over from winter if you overwatered in February or March. The larvae are in the soil. Let soil dry appropriately between waterings to break the reproductive cycle — soggy May soil keeps the population going.

If you're seeing active thrips or spider mite damage, treatment is warranted:

Isolate affected plants immediately before treating — thrips especially move between plants in your collection with alarming speed.

Tasks for this month

  • Move tropicals away from direct south-window sun — calathea, alocasia, peace lily, and ferns need shade cloth or distance from intense May sun.
  • Increase watering frequency based on soil checks, not a rigid schedule.
  • Fertilize at full strength for established plants in active growth. A balanced liquid fertilizer (10-10-10 or similar) diluted per label instructions, applied monthly, fits the once-or-twice-a-month schedule Iowa State Extension gives for most houseplants.
  • Check for thrips on every new leaf — look at the underside and in the curl of an unfurling leaf for tiny flying or crawling insects.
  • Assess humidity — if AC is running, add pebble trays or a humidifier near calathea and ferns.
  • Repot any remaining root-bound plants you missed in March and April — May is still within the repotting window, which Clemson HGIC puts in spring and summer while the plant is actively growing.
  • Clean leaves — a wipe-down with a damp cloth removes dust buildup that reduces photosynthetic efficiency. Larger-leafed plants like monstera and fiddle leaf fig benefit the most.

Plants to focus on in May

Calathea (Calathea spp.)

Calathea hits its stride in May with genuine new-leaf production — look for tightly rolled new leaves unfurling from the center of the plant. These are the most humidity-sensitive leaves; if the air is too dry, new leaves often emerge with brown edges right out of the gate.

The ASPCA lists Calathea as non-toxic to cats and dogs — one of the few tropical houseplants on the ASPCA's non-toxic list. See calathea care for full growing notes.

Calathea needs indirect light — keep it back from south and west windows in May, or behind a sheer curtain. Water before the soil goes completely dry.

Alocasia (Alocasia spp.)

Alocasia is a dramatic grower in May. New leaves emerge quickly on established plants, and the large, architectural leaves need consistently high humidity or they develop brown edges and tips. This is the plant that most directly benefits from a humidifier or a spot in a bathroom with natural humidity.

The ASPCA lists Alocasia as toxic to cats and dogs via insoluble calcium oxalates — clinical signs include oral irritation, excessive drooling, and difficulty swallowing. Keep out of reach of pets. See alocasia care for details.

Peace Lily (Spathiphyllum spp.)

Peace lily is at its most active in May, pushing new leaves and occasionally spiking into bloom. It wants bright indirect light — a north-facing room that was too dim in winter can now provide enough light near the window.

The ASPCA lists Peace Lily as toxic to cats and dogs via insoluble calcium oxalates. It's a common houseplant to keep out of reach of pets despite its reputation as a "safe" plant — it isn't.

Water peace lily when it begins to droop slightly — that's its signal.

Monstera (Monstera deliciosa)

Monstera unfurls large new leaves throughout May in good light. A well-established monstera in a bright indirect spot keeps pushing new leaves during peak season. Support with a moss pole or stake — the plant wants to climb.

The ASPCA lists Monstera deliciosa as toxic to cats and dogs via insoluble calcium oxalates. See monstera care for full growing details.

Pothos (Epipremnum aureum)

Pothos is the forgiving baseline plant that continues to perform in May. It tolerates indirect light from any window direction, accepts irregular watering better than most tropicals, and grows vigorously in peak season. Pothos works as a canary of sorts — if even the pothos looks unhappy, something is genuinely wrong.

The ASPCA lists Golden Pothos as toxic to cats and dogs via insoluble calcium oxalates. See pothos care for full details.

What NOT to do in May

Don't move plants to full outdoor sun immediately. If you're thinking of giving plants a summer vacation outdoors (more on this in July), May is too early for most tropical houseplants. Even shade-lovers need hardening off — a sudden transition from indoor filtered light to outdoor ambient light causes light stress and bleaching.

Don't let south-window tropicals bake. May sun through glass is intense enough to cause real leaf scorch. Check regularly.

Don't skip fertilizer this month. Iowa State Extension names spring and summer as the best times to fertilize houseplants. Skipping it when plants are in active growth leaves them drawing on whatever reserves are in the soil.

Don't ignore the first signs of pest damage. A single thrips-infested leaf can become a collection-wide infestation if you don't isolate and treat quickly. Early intervention is dramatically easier than cleanup after a population boom.

Don't overwater enthusiastically. Active growth does increase water demand, but the answer is to check the soil more frequently, not to water more heavily each time. Root rot from oversaturation is a spring killer.

Don't repot into a pot that's drastically larger. When repotting, go up one pot size: Clemson HGIC advises a pot 1 or 2 inches larger in diameter. A very large pot holds soil that the roots can't reach, that soil stays wet, and you get root rot.

Frequently asked

Why are my calathea's new leaves coming in with brown edges?

This almost always comes down to low humidity, not watering. Calathea new growth is the most sensitive tissue on the plant — it emerges from the tightly rolled new leaf bud and, if the ambient air is too dry, the leaf edges desiccate before the leaf even fully opens. If you have AC running in May, it's likely pulling humidity below what calathea prefers. Add a pebble tray under the pot, group plants together, or place a small humidifier nearby. Once a new leaf opens with brown edges, the damage is permanent — but subsequent new growth will be fine if you address the humidity.

Should I fertilize in May, and with what?

Yes — May is one of the best months to fertilize because plants are actively growing and can use the nutrients immediately. A balanced liquid fertilizer (equal NPK ratios, something like 10-10-10 or 20-20-20) applied once or twice a month during the growing season is what Iowa State Extension advises for most houseplants. Follow label directions for dilution. Don't fertilize freshly repotted plants: Iowa State advises waiting at least 2 to 4 weeks, since most potting soil already contains some fertilizer. Also don't fertilize a plant that's stressed, rootbound to the point of being unhealthy, or showing signs of pest damage — treat the problem first.

My plant has tiny flying insects around the soil. Is that fungus gnats or something else?

Almost certainly fungus gnats. They're the most common soil-dwelling pest of houseplants and are almost always caused by soil that stays too moist. The adult gnats are harmless but annoying; the larvae feed on fungal material and fine root hairs in the soil. To confirm, UC IPM notes that chunks of raw potato placed cut side down on the soil are used to monitor for larvae; check them and replace infested chunks after a few days. The fix is cultural: let soil dry out more thoroughly between waterings. For active infestations, a drench with Bacillus thuringiensis israelensis (BTi) — a biological larvicide available under brand names like Gnatrol — kills the larvae without harming plants or soil biology. Sticky yellow traps catch adults.

Sources: ASPCA — Calathea · ASPCA — Alocasia · ASPCA — Peace Lily · ASPCA — Swiss Cheese Plant (Monstera) · ASPCA — Golden Pothos · NC State Extension — Calathea zebrina · UC IPM — Fungus Gnats · UC IPM — Spider Mites · Iowa State Extension — How to Care for Houseplants · Iowa State Extension — Fertilizing Houseplants · Clemson HGIC — Transplanting and Repotting