Gadenin日本語Get the appThe shape of the season
Radicchio's year has four clear phases and they do not divide evenly. There is a short establishment phase, then a long, dull, apparently unproductive growing phase through warm weather, then a fast heading phase triggered by cold nights, and finally a long harvest window that runs deep into the cold. Most of the mistakes made with this crop come from misreading the second phase as failure.
The whole thing is anchored to one date, your first hard frost, and everything is counted backwards from it. Sow 90 to 110 days before that date. Everything else follows from where the weather is relative to that sowing.
Work in stages rather than dates. A cold autumn compresses the heading phase and a mild one stretches it out by weeks, so the plant tells you where it is more reliably than any calendar does.
| Stage | Roughly when | Main jobs | Decision point |
|---|---|---|---|
| Sowing and establishment | 90 to 110 days before first hard frost | Sow shallow in stations, keep moist, thin twice | Are plants at final spacing by six leaves? |
| Green growing phase | The following six to eight weeks | Water evenly, one feed early then stop, weed under the canopy | Is the crown flat, or is a stem rising? |
| Heading and coloring | As nights fall into the 40s F (4 to 10C) | Strip flat lower leaves, keep the crown clear, reduce water | Still open and green late on? Cut back to a stump |
| Harvest and holding | First frosts onward | Squeeze-test weekly, cut as needed, leave stumps in | Any head spongy or split? Cut it now |
| Overwintering | Deep cold onward | Cover to shed rain, leave stumps and late plants standing | Is the crown alive and firm? |
Phase one and two: get it established, then leave it alone
For the first month the only jobs are keeping the surface moist enough for even germination and thinning hard to one plant a station. Everything you get later depends on spacing, and this is the only window in which spacing can be set. A single balanced feed a few weeks after thinning covers the plant's whole nutritional requirement in most soils.
Then comes the long stretch where nothing appears to happen. The plant sprawls, stays green, and looks like a rather coarse lettuce that has forgotten what it is for. This is correct. It is building the leaf area and root that will pay for the head. Your jobs are watering evenly, keeping weeds out from under the canopy, and resisting the urge to feed it into looking better.
The one thing worth checking through this phase is the growing point. A flat, tight cluster of small leaves at the center means the plant is waiting. A thickening stem pushing upwards out of the center means it has bolted, and that plant should come out now rather than occupy space until autumn.
Phase three: the cold does the work
When nights start dropping into the 50s F (10 to 15C) and then the 40s F (4 to 10C), the plant changes mode. Outward growth stops, the inner leaves begin to cup, and red starts appearing in the veins before spreading across the blade. From the first sign of cupping to a firm head is usually three to five weeks depending on how cold it gets.
Your jobs shift entirely to keeping the plant dry and open at the base. Strip lower leaves that yellow or lie on the soil, pull mulch back from the crowns, take out any late weeds, and cut watering right down. A head that fills in wet soil packs loosely and stores badly.
This is also the moment to deal with stubborn plants. If the nights have been genuinely cold for two or three weeks and a plant is still flat and green, cut it off an inch (2 to 3 cm) above the crown and let it regrow. What comes back from the stump in cold weather is tight and red, and it will usually be ready four to six weeks later.
- Watch the growing point weekly Cupping inner leaves means the plant has switched to heading. A thickening upward stem means it has bolted and should be pulled.
- Strip and clear the base Take off flat and yellowing lower leaves, weed under the canopy and pull mulch back to leave clear soil around each crown.
- Cut water right back Give only enough to prevent wilting once the head is filling. Lean growing gives a denser head that stores far longer.
- Cut back the stragglers Any plant still open after two or three weeks of cold nights gets cut to a stump. Give it four to six weeks to make a heart.
Phase four: harvest, hold, and what to write down
Once the first frosts arrive the crop is at its best and can simply stand in the ground. Squeeze-test the heads weekly and cut what you need, taking the head an inch (2 to 3 cm) above the crown and leaving the stump to push a second flush of small colored leaves. Cut anything spongy or split at once regardless of whether you want it, because it will not improve.
In a climate of light frosts the row may hold for a month or more. Where the ground freezes solid, cut the standing heads before that happens; a head frozen through and thawed collapses. Late or undersized plants can be left standing, since they often overwinter and heart in early spring.
Four dates are worth writing down each year: the sowing date, the date you first saw red veining, the date of your first frost, and the date you cut the last head. Add a note of which end of the bed did well. After two seasons those numbers set your sowing window precisely for your own garden, which is something no general calendar can do.
Keep the bed plan with the dates. Radicchio in ground that grew a heavily fed crop the previous season tends to stay green and open, so knowing what preceded it explains most of the variation between rows.