Gadenin日本語Get the appThe head is made from leaves the plant already has
Cabbage grows in two phases. First it builds a rosette of large open outer leaves, and then, once it has enough of them, the newer leaves at the center start to cup inwards and wrap, and that wrapping is the head. Nothing you do during the second phase adds much: the head can only be as big as the leaf area the plant built during the first phase. This is why the decisions that determine head size are all made weeks before you see any sign of a head.
A plant needs roughly 12 to 15 well grown outer leaves before it will begin to cup. If you count fewer than ten large leaves and the center is already closing, you are going to get a small head no matter how you feed it from here. If the plant has twenty big leaves and is still sprawling open, it is building an excellent frame and the head is coming.
| What the plant looks like | Phase | Outlook |
|---|---|---|
| Open rosette, leaves getting larger each week | Building the frame | On track. Keep feeding and watering |
| Center leaves cupping inwards, edges curling up | Heading has started | Three to six weeks to a cut head |
| Center firm and tight to the touch | Filling | Check firmness weekly, stop feeding |
| Twenty leaves, still flat and open, late in the season | Stalled | Too much nitrogen or too little light |
Heads that stay loose and open
A loose head, one that looks like a head but gives when you squeeze it and has gaps between the leaves, is nearly always nitrogen. Feeding heavily once the center has started to cup keeps the plant producing soft leaf rather than packing what it has, and each new leaf pushes the previous one outwards instead of wrapping over it. Stop feeding nitrogen the moment you can feel the center beginning to firm.
The second cause is heat. Cabbage packs its head properly at daytime temperatures between about 59F and 68F (15C to 20C), and above roughly 77F (25C) the wrapping goes loose and unreliable. A crop that is heading through the hottest weeks of summer will disappoint however well you grow it, which is why cabbage is planted so that heading falls in cool weather at either end of the season.
Shade is the third. A cabbage needs at least six hours of direct sun, and a plant under a tree or crowded by its neighbors will make thin, wide leaves that do not have the substance to wrap tightly.
- Stop nitrogen when the center cups Feed generously up to the point where the inner leaves start curling inwards, then stop. Any nitrogen after that goes into loose leaf, not into a firm head.
- Shade the crop in a hot spell If a heatwave arrives while the heads are filling, 30 to 50 percent shade cloth over the row keeps the plants several degrees cooler and noticeably improves how tightly they pack.
- Take out competition, not the outer leaves Weed thoroughly around the plants and remove any crowding neighbor, but leave every healthy outer leaf on the cabbage. Those leaves are what fills the head.
Plants that never head at all
A cabbage that sits as a flat rosette all season and never closes has usually had its root system checked at some point. A plant that was held too long in its cell, or planted into cold or waterlogged ground, or bitten off at the roots by cabbage root fly, spends the season simply staying alive. Lift a non-heading plant at the end of the season and look at the roots: knobbly galls mean clubroot, tunneled and rotten roots mean root fly, and a tight coiled mass means it was potbound when you planted it.
The other reason is simply time. Cabbage needs 60 to 100 days from transplant to a cut head depending on type, and a plant set out too late runs into weather that is too hot or too cold before it has built its frame. Where the season ends against you, cut the plant and use the open leaves: they are perfectly good eating, just not a head.
| Symptom | Likely cause | What to do next year |
|---|---|---|
| Flat rosette, small pale leaves, never grew away | Root damage or potbound transplant | Plant younger seedlings, check the rootball |
| Wilts in the day, roots tunneled | Cabbage root fly | Mesh and stem collars from planting day |
| Swollen distorted roots with galls | Clubroot | Lime hard, move the crop, allow many years |
| Good big leaves but ran out of season | Planted too late | Sow four to five weeks earlier |
Bolting: a flower stalk instead of a head
Cabbage is biennial. It is supposed to head in its first season, sit through winter and flower in its second, but a young plant exposed to sustained cold can be tricked into thinking a winter has passed and it will run straight to a flower stalk. The trigger is roughly two to four weeks below about 55F (13C) on a plant that already has a stem thicker than a pencil. A very small seedling is not susceptible; that is exactly why sowing too early is the risk.
Once the stalk elongates and you can see the head splitting open around it, the plant will not recover. Cut it and eat it immediately, because the leaves are still fine but they turn bitter and tough as the stalk extends. Prevention is a matter of timing: for a crop that grows through cool weather, avoid setting out plants that are already large into a run of cold, and if unseasonable cold is forecast, cover the row with row cover for the duration.
- Do not sow too early Sowing earlier does not get you an earlier head. It gets you a plant of exactly the wrong size going into cold weather, which is the size that bolts.
- Row cover the row through a cold snap Two or three weeks of cold on a pencil-thick plant is enough to trigger bolting. Row cover over hoops through that period costs almost nothing.
- Cut a bolting plant at once The eating quality drops daily once the stalk starts to extend. Cut it, strip the leaves and use them straight away rather than hoping it settles down.
Heads that split open
A firm head that splits from the top has taken up water faster than it can expand. The classic sequence is a dry spell while the head is filling, then heavy rain, and the inside grows so fast that it bursts the outer wrap. A split head rots within days once rain gets into the crack, so this is a race you want to avoid entering.
The reliable prevention is even moisture: mulch the bed and water when the soil dries rather than letting it swing between bone dry and soaked. The second prevention is not leaving mature heads standing. Once a head feels solid, it is ready, and every extra week in the ground is another chance for rain to split it.
- Cut ahead of forecast rain If the heads are firm and heavy rain is coming, cut them. A cabbage keeps for weeks in cool storage and for no time at all once it has split.
- Give the plant a twist Where you cannot cut yet, take hold of the head and turn it about a quarter turn to break some of the roots. That slows water uptake and buys you a week or two.
- Mulch to even out moisture Straw or compost around the base stops the soil drying hard between waterings, which is what sets up the sudden uptake that splits heads.
Record the date the center first cupped and the date you cut. The gap between those two is the number you need to plan next season, and it will be shorter in warm weather and longer in cool.