Gadenin日本語Get the appThere is no interval, only a cycle
Watering a cactus on a fixed weekly schedule is the fastest way to lose it, because the same plant dries in four days on a hot windowsill in a clay pot and in three weeks in a plastic pot in a cool room. What stays constant is the cycle: soak thoroughly, let the compost go completely dry, wait a few days more, then soak again.
The waiting after it dries is the part people leave out. Roots need a spell of dry air around them to take up oxygen, and compost that is never quite dry is what breeds the root rot you only discover when the plant falls over.
| Pot and position | Time to dry through in summer | How to handle it |
|---|---|---|
| Clay pot, sunny window, gritty mix | Four to seven days | Water two or three days after it dries |
| Plastic pot, sunny window, gritty mix | Eight to twelve days | Check with a skewer before every watering |
| Plastic pot, peat-based compost, cool room | Three weeks or more | Repot into a gritty mix rather than water less |
| Outdoors in full sun, small pot | Two to four days | Water in the evening in a heatwave |
Checking whether it is dry
The surface of a gritty mix looks dry within hours of watering, so what you can see on top tells you nothing. Judge by weight or by probing to the bottom of the pot.
- Learn the pot by weight Lift the pot straight after watering and again a fortnight later. The difference is obvious once you have felt it twice, and after that you can decide in a second without touching the compost.
- Probe with a wooden skewer Push a long skewer down the inside wall of the pot to the base and pull it out after ten seconds. Any darkening or clinging grit means it is still damp inside. Wait.
- Look at the body in strong light A cactus that has drawn on its own reserves loses a little gloss and the ribs draw slightly closer together. That is the ideal moment to water, not a sign you left it too long.
When you water, water properly
Small sips wet only the top inch of compost, leave the roots at the bottom permanently dry and the middle permanently damp, and encourage a shallow root plate. Water until it runs freely from the drainage holes, every time.
- Water the compost, not the plant Pour at the edge of the pot and keep water off the body. Water sitting in the crown of a globular cactus, or in the woolly top of a mature one, is a common start to rot.
- Let it drain, then empty the saucer Give it ten minutes and tip away everything in the saucer. A pot standing in half an inch of water for a day is enough to damage roots at the base.
- Water in the morning in cool weather In spring and autumn, water on a bright morning so the compost surface and any splashes dry before the night temperature drops.
- In a heatwave, water in the evening At above 95F (35C) many desert cacti stop growing anyway. Water after the sun is off the pot, so the roots are not sitting in hot wet compost at midday.
Standing the pot in a bowl of water to soak from below is fine, but take it out after twenty minutes. Leaving it there for an afternoon saturates the compost far past what the roots can use.
The year in water
The single biggest change through the year is not the interval but whether you water at all. The plant stops growing at both ends of the year, and water it cannot use is water that sits in the pot doing harm.
| Season | Interval | Notes |
|---|---|---|
| Early spring, before growth restarts | One light watering, then wait | Give about a quarter of a normal soak to wake the roots |
| Spring into summer, in growth | Soak whenever it has been dry two or three days | Usually every one to two weeks |
| High summer above 95F (35C) | Stretch the interval | Growth pauses. Water in the evening only |
| Autumn, as nights cool | Halve the frequency, then stop | Last watering roughly a month before the cold room |
| Winter below 50F (10C) | None at all | Dry compost is what makes the cold safe |
| Winter in a warm room above 59F (15C) | A small amount monthly | It cannot rest properly. Keep it as bright as possible |
A cactus shrinks and wrinkles a little over a dry winter, and that is normal. It plumps up within a fortnight of the first spring watering. Watering because of winter wrinkling is the classic mistake.
Telling too much water from too little
Both extremes soften the plant, which is why they are confused so often. The difference is where the softness is and what the compost feels like.
| What you see | Compost | Cause and action |
|---|---|---|
| Soft, darkened, slightly sunken at soil level | Damp | Basal rot. Unpot today and cut above the damage |
| Whole body soft, yellowish, base still firm | Damp | Overwatered. Stop, move it to air and light |
| Body shrunken, ribs pulled in, still firm | Bone dry | Thirst. A full soak restores it in about ten days |
| Firm but not growing at all in summer | Dry for weeks | Underwatered in growth. Restart the normal cycle |
| Split running down one side after watering | Very wet after a long dry spell | Water taken up too fast. It scars over. Water more evenly |
What to note down
Write down the date of the last watering before the winter rest and the date of the first watering in spring, for each plant. Those two dates are the whole framework of the year, and comparing them against whether a plant flowered tells you more about your own conditions than any general advice can.