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Taro is a tropical plant and it measures the season by soil temperature alone. Below 60F (15C) a planted corm simply sits, and every week it sits in cold wet ground is a week in which rot organisms get a head start on the sprout. The trigger to plant is soil at four inches (10 cm) deep reading steadily above 65F (18C), which in most temperate gardens is two to four weeks after the last frost, later than almost anything else you put in.
The reason to be strict about this is that taro needs a very long run: 180 to 210 frost-free days from planting to a full-sized main corm, and even the quicker types want 150. Count the days between your last spring frost and your first autumn frost before you start. If the number is under 150, you can still grow taro, but plan to start the corms indoors in pots six weeks early and to accept smaller corms.
| Soil at 4 in (10 cm) | What happens to a planted corm | Verdict |
|---|---|---|
| Below 60F (15C) | No sprouting, skin softens, rot begins | Do not plant |
| 60 to 64F (15 to 18C) | Slow, uneven emergence over five weeks | Only under black plastic |
| 65 to 72F (18 to 22C) | Emergence in two to three weeks | The right window |
| Above 75F (24C) | Emergence in ten to fourteen days | Ideal, but leaves less season ahead |
Choosing and preparing the seed corm
A seed corm is a small whole corm or a side corm saved from last year's crop, roughly the size of an egg to a small fist. Bigger is not better beyond a certain point; a corm of about three ounces (85 g) with a firm, dry skin and a visible bud at the crown outperforms a large soft one every time. Reject anything that gives under thumb pressure, weeps, or smells sour, because soft rot travels with the planting material and no amount of good ground will rescue it.
Handle seed corms with the same caution you would use on a mature one. The sap contains needle-shaped calcium oxalate crystals that will make your hands itch and burn for hours, and the reaction is worse if you have cut skin. Wear gloves for planting, and do not rub your eyes while you work. If the corm has already begun to sprout in storage, that is a good sign and the sprout should be planted upward and unbroken.
- Pick firm corms with a live bud Press with a thumb. A sound seed corm feels like a potato, not a plum. Look for a pointed bud or a short pink shoot at the crown end.
- Do not cut corms into pieces Unlike potatoes, taro corms cut into sections rot far more often than they grow. Plant small corms whole, or use side corms from last season.
- Wear gloves from the start The sap irritates skin badly. Gloves at planting, at hilling and above all at harvest. Wash tools and hands before touching your face.
- Sprout early if your season is short Pot corms into damp compost in a warm place six weeks before your planting date. Set them out with the shoot already four inches (10 cm) high.
Ground that holds water rather than draining it
Almost every other vegetable page tells you to improve drainage. Taro is the exception. It evolved in swamp margins and it grows best in ground that stays wet, so the ideal bed is the low corner of the garden, heavy soil, or a shallow basin you deliberately build to trap irrigation. A raised bed on light sand is the worst possible choice and will cost you far more watering than the crop is worth.
Work plenty of well-rotted manure or mature compost into the top twelve inches (30 cm) before planting. Taro is a heavy feeder over a very long season, and organic matter does two jobs here: it supplies the nitrogen the huge leaves need, and it holds moisture between waterings. Aim for a pH between 5.5 and 6.5. If your ground is genuinely free-draining sand, dig a trench a foot deep, line it with a sheet of plastic punched with a few holes, and refill it; that single measure turns an impossible site into a workable one.
| Site | Suitability | What to do about it |
|---|---|---|
| Heavy clay, low-lying, slow to drain | Excellent | Add compost for feed, nothing for drainage |
| Ordinary loam | Good | Plant in a shallow basin to hold water |
| Free-draining sand | Poor | Line a trench with perforated plastic, or grow in tubs standing in water |
| Beside a pond or ditch | Excellent | Plant at the margin where soil stays saturated |
| Raised bed with sharp drainage | Avoid | Use it for something else and find lower ground |
Depth, spacing and getting the corm in the ground
Plant seed corms four inches (10 cm) deep with the bud pointing upward. Shallower planting brings the developing main corm too close to the surface, where it greens and cracks; deeper planting in cold spring soil delays emergence by another week or more. Allow two feet (60 cm) between plants and thirty to thirty-six inches (75 to 90 cm) between rows. That looks absurdly generous when you are setting out corms the size of an egg, and completely justified by midsummer, when each plant carries leaves three feet across.
Set the plants in a shallow trench rather than on a ridge, four to six inches (10 to 15 cm) below the level of the surrounding bed. The trench collects rain and irrigation and delivers it exactly where you want it. As the season goes on you will fill this trench in gradually while earthing up, so by late summer the row sits level or slightly proud. Water thoroughly after planting and then keep the ground damp, never dry, until the shoots appear.
- Open a trench, not a ridge Draw a trench six inches (15 cm) deep along the row. Plant into the bottom of it so every drop of water runs to the plants.
- Set corms bud up, four inches deep Cover with four inches (10 cm) of soil above the top of the corm. Firm it lightly with the flat of your hand, not your heel.
- Space two feet apart Two feet (60 cm) in the row, thirty inches (75 cm) or more between rows. Crowded taro makes leaves and few side corms.
- Water in and keep it damp Soak the trench at planting and never let it dry out while you are waiting for emergence. Dry soil at this stage kills the sprout outright.
Do not start worrying if nothing shows for three weeks. Taro emerges slowly and unevenly, and gaps in the row often fill in a fortnight after the first shoots appear. Dig a corm up to check only after four weeks of warm soil with no sign.
The first month, and what to write down
From planting to the first unfurled leaf takes two to four weeks in warm ground. During that time the only job is keeping the trench damp and the weeds off, because young taro competes badly and the leaves that will later shade out everything are not there yet. Once three leaves are up, growth accelerates sharply and the plant needs the water and the feeding described on the watering and hilling pages.
This is the point to start a record, because taro gives you almost no information above ground for the rest of the year. Note the planting date, the soil temperature you planted at, the position and number of corms in each row, and the date each plant emerged. Late emergers are worth marking with a cane: at harvest you will find out whether they caught up, and that tells you far more about your own site than any general guidance can.
- Keep the row damp until emergence Check every second day in warm weather. The corm has no roots yet and cannot fetch water from any depth.
- Weed by hand for the first six weeks Weeds beat young taro easily. Once the canopy closes over the row, almost nothing germinates beneath it and you can stop.
- Mark late emergers with a cane Note which positions came up two weeks behind. Comparing their corms at harvest tells you whether a slow start matters in your garden.
- Record the planting date and soil temperature Write down the date, the reading at four inches (10 cm), and where each row is. Next season you will know whether you planted too early or too late.