How to water houseplants: the definitive guide

The golden rule: don't follow a fixed calendar

The most common mistake is watering "every Sunday" or "twice a week" regardless of conditions. Every plant uses water differently depending on species, season, temperature, air humidity, pot size, light exposure and vegetative activity. A pothos in a low-light bathroom can go two weeks without water; the same pothos in a kitchen by a south-facing window may want water weekly.

The correct rule is: water only when the substrate calls for it, checked before every watering.

How to check if water is needed

There are three reliable methods, in increasing order of precision:

• The finger test: push your finger into the soil to the second knuckle (about 3 cm). If it's dry, water. If it's still moist, wait.
• The weight test: lift the pot. With experience you learn to tell a heavy (wet) pot from a light (dry) one. Many experienced growers use only this method.
• The soil moisture meter: a small, cheap probe that goes into the substrate and displays the humidity level. Useful especially in large pots where your finger doesn't reach the roots.

How to water correctly

When the time comes, water generously: pour until water flows from the drainage holes. This ensures the whole substrate is soaked and excess salts are flushed. Wait 15-30 minutes and empty the saucer: standing water is the main cause of root rot.

Shallow waterings (a little water every day) are wrong: they wet only the top of the substrate without reaching deep roots, which then wither.

What water to use

Tap water is fine for most plants, with two caveats: use it at room temperature (never cold straight from the tap in winter) and, if it's hard, let it stand 12-24 hours in an open watering can so the chlorine evaporates.

Plants sensitive to limescale and chlorine (calatheas, ferns, orchids, carnivorous plants, gardenia, hydrangea) prefer rainwater, demineralised water (from the supermarket) or filtered water. In winter, with heating on, lukewarm water (18-22°C) is always better than cold.

Watering from the top or from the bottom?

Top watering (pouring water directly onto the substrate) is the standard method and works for almost every plant. It's quick and flushes salts.

Bottom watering / soaking (placing the pot in a container of water for 15-30 minutes until the top of the substrate is wet) is best for: African violets and hairy-leaved plants that don't tolerate water on top; orchids (bark substrate tends to repel water from above); plants with very dry substrate that repels water; succulents and cacti.

Indicative frequency by plant type

• Succulents and cacti: every 2-4 weeks in spring-summer, once a month in autumn-winter. Substrate must dry out completely.
• Snake plant, ZZ plant: every 2-3 weeks, drought-tolerant.
• Pothos, philodendrons, monstera: when the top 3-4 cm is dry, generally 5-10 days.
• Ficus, dracaena, kentia: when the top 3-4 cm is dry, 7-10 days on average.
• Calatheas, maranta, ferns: substrate consistently moist but never soaked, every 3-5 days.
• Orchids: by soaking every 7-10 days; the bark substrate must dry between soakings.
• Basil, potted culinary herbs: when the top 2 cm is dry, often every 1-2 days in summer.

Common mistakes to avoid

• Watering "on a schedule" every N days without checking the substrate.
• Small daily waterings instead of generous, spaced-out ones.
• Leaving water in the saucer for days.
• Using cold water in winter.
• Watering succulents like calatheas.
• Not reducing watering in winter when the plant is dormant.
• Wetting hairy leaves (African violets, saintpaulia): they can develop spots.

Watering during holidays

For 1-2 week absences: wick systems (a string from the pot to a water reservoir next to it) or terracotta bulbs with a reservoir work well for most plants. Move plants into indirect light before you leave and water generously that day: many houseplants survive 2 weeks of moderate drought without issues, while just a few days of overwatering can kill them.