Gadenin日本語Get the appWhy turmeric has to start indoors
Turmeric needs eight to ten months of continuous warmth between the day a shoot appears and the day the leaves die down. Almost nowhere outside the subtropics gives you that outdoors, so the season has to be borrowed at the front end. You start the rhizome in a warm room in late winter, long before anything else in the garden is moving, and it spends its first two or three months growing under a roof.
The practical consequence is that the planting decision is made twice. The first planting is into a small container indoors, where the only thing that matters is warmth. The second is the move outdoors, or the potting-on into the container the plant will finish in, once nights are reliably above 55F (13C). Treat them as one continuous operation and you will lose the crop to a cold snap in the middle.
A rhizome that has not sprouted by the time the weather warms has lost the whole season. There is no catching up later: turmeric grows at the pace warmth allows, and a plant that starts in early summer simply runs out of months before the leaves yellow.
Choosing and waking the rhizome
Turmeric planting stock is the same thing you cook with, and a firm rhizome from a grocery shelf will grow. Look for pieces that are heavy for their size, with tight unwrinkled skin and small blunt swellings on the knuckles. Those swellings are the growth buds. Skip anything that is light, shriveled, soft at one end, or has been kept in a chilled cabinet, because sustained temperatures below 50F (10C) kill the buds without changing how the piece looks.
To sprout it, half-bury the rhizome in barely damp potting mix in a shallow tray, cover it loosely to hold humidity, and keep it at 77 to 86F (25 to 30C). On a heat mat the first pale-pink tips push through in two to three weeks. At ordinary room temperature it can take six weeks or never happen at all. Warmth is the only variable that matters here; light does nothing until a green shoot is actually above the surface.
- Buy more than you need Some proportion of any batch has been chilled or treated to suppress sprouting. Start four or five pieces even if you only want two plants, and plant on the ones that respond.
- Divide at the knuckles Snap the hand apart at the narrow waists rather than cutting through thick tissue. Each piece should weigh at least one and a half ounces (40 g) and carry two or three visible buds.
- Let cut faces dry Where a knife was unavoidable, leave the pieces on a dry surface out of the sun for a day or two until the cut goes dull and leathery. A wet cut face planted straight away is the usual way rhizomes rot.
- Keep the medium wrung-out damp It should feel like a cloth you have squeezed, not like wet soil. Standing moisture at this stage rots the piece before it can sprout, and nothing about the surface will warn you.
Depth, spacing and the pot that finishes the crop
New rhizomes form above the piece you planted, not below it, and they spread sideways in the top six inches (15 cm). That single fact settles every question about depth and container shape. Set pieces two inches (5 cm) deep with the buds pointing up. Deeper does not protect them and only makes the shoot travel further through cool soil.
In the ground, space plants twelve to sixteen inches (30 to 40 cm) apart. In containers, give one plant at least five gallons (19 L) and preferably seven to ten (26 to 38 L), in a pot that is wide rather than tall. A cramped pot does not kill turmeric; it just caps the harvest, and you will not find that out until you tip it out in autumn. Use a free-draining mix with plenty of compost, aiming for a pH of 5.5 to 7.0.
| Decision | In the ground | In a container |
|---|---|---|
| Planting depth | 2 in (5 cm) | 2 in (5 cm), pot filled two thirds |
| Spacing per plant | 12 to 16 in (30 to 40 cm) | 5 to 10 gal (19 to 38 L) each |
| Pot shape | Not applicable | Wide and shallow beats deep and narrow |
| Soil temperature to plant out | Above 68F (20C) | Above 68F (20C) |
| Night temperature to move outdoors | Above 55F (13C) | Above 55F (13C) |
Moving outdoors without checking the plant
By the time nights are warm the indoor plants have soft, thin leaves grown under glass, and full sun on the first day will scorch them into brown paper. Harden them off over a week to ten days: an hour of morning sun on the first day, building up, and back under cover before evening if the forecast dips.
Fill the final container two thirds full so you have room to top it up later. Turmeric responds to soil mounded around the base of the shoots the way potatoes do, and the space you leave in spring is what makes that possible in midsummer. Water the pot through once after potting up, then leave it alone until the surface dries; a newly potted rhizome with few roots cannot drink what a full pot holds.
What to write down at planting
Turmeric's timeline is too long to hold in your head, and the decisions you will second-guess in autumn were all made in late winter. Record the date the rhizome went onto the heat mat, the date the first tip broke the surface, and the weight of the piece you planted. Next year those three numbers tell you whether to start earlier and whether bigger starting pieces were worth it.
Note where each plant sits too. Turmeric leaves look identical, and once you have two or three going, the only way to connect an autumn harvest weight back to a spring planting piece is a position noted at the time. Add the date you moved plants outdoors and the night temperature that week, because that is the number you will want when a spring turns out colder than the last one.