Why Are My Cabbages Not Forming Heads?

When cabbages are first planted they initially produce lots of large broad leaves, but in the latter part of their growing season the inner leaves at the centre of the plant begin curling inwards and cupping around a short-thick stem, growing tightly together to form the head of cabbage we are all familiar with. The cabbage head is the only part that’s eaten, and it’s what we see sold at produce markets and greengrocers with the outer leaves removed.

Cabbage Varieties

Cabbages are cool season crops from the Brassicaceae (mustard) family that are harvested in 8-15 weeks after planting from seed. The time to maturity varies depending on the variety.

There are three major groups of cabbage varieties,  the green and red cabbages (Brassica oleracea var. capitata) and the Savoy cabbage (Brassica oleracea var. sabauda).

• Green cabbages have smooth textured leaves which are pale green to dark green in colour.
  
• Red cabbage have smooth textured leaves which are either crimson or purple in colour with white veins.
  
• Savoy cabbage have more ruffled leaves which are yellowish-green in colour.

If growing conditions are right, then cabbages will form heads, so being patient and allowing the plants to go through their natural growth cycle in their own time may be all that’s required. The cabbage pictured in this article was planted in the cooler seasons and is starting to form a head in mid-spring.

But what if the 15 weeks have passed and the cabbages still aren’t forming heads?

Cabbage Growing Requirements

Cabbage need full sun, and a well-drained but moisture-retentive, fertile soil with a pH of 6 to 7. These plant are heavy feeders and need a steady supply of nutrients and water during their growing period. It’s best to fertilise the soil before planting by mixing in manure to boost soil fertility. Additional fertiliser can be used throughout the growing season, but the plant should not be given any fertiliser when the head starts to form.

The Top 7 Reasons Why Cabbages Wont Form Heads

Different varieties of cabbage vary in the days required to reach maturity, some take longer than others. It’s also important to be aware that some cabbage varieties produce a looser heads, which aren’t as dense. That said, the main cause of cabbages not forming heads, or only forming loose, puffy heads, is improper growing conditions, which stress the plant or stunt its growth.

Here are main reasons why cabbages won’t form heads:

1. High Temperatures

Cabbages require cool temperatures to form a head, so it’s important to plant cabbages at the right time of the year (consult a gardening calendar) so the head will have time to form when daytime temperatures are still below  27°C (80°F).

If it gets too hot, plants may stop growing leaves and instead send up a flower stalk and go to seed, which is known as ‘bolting’.

2. Inconsistent Watering

For cabbages to grow, they require adequate moisture. If they’re not watered consistently, or don’t receive regular rainfall, they will develop a poor texture, become excessively bitter, and may not form a head. Good quality heads of cabbage should be firm, crisp, juicy, and sweet, they may sometimes be peppery, but not definitely bitter.

Depending on rainfall, cabbages may need watering around 2 – 3 times a week, but be careful not to overwater them as this may cause the heads to split! Water the plants early in the morning, as this allows the leaves to dry out in the sun during the day, and helps prevent common fungal diseases.

3. Excessive Cold

Extended periods of cold weather may cause the cabbages to stop growing and become dormant. If this happens, the plants will often ‘bolt’ (flower and go to seed) when the weather warms up and growth resumes once again.

Cold temperatures won’t kill off cabbage plants, but frost can damage their leaves. If young seedlings are frost damaged, their growth can be stunted, so it’s advisable to cover with cloth or hessian to protect them on frosty nights.

4. Nitrogen Deficiency

All plants require nitrogen as a nutrient to produce leafy green growth. Brassicas are heavy feeders, so they require high soil fertility to provide sufficient nitrogen for their growth demands.

Adding slow-release fertilisers such as manures, blood and bone or a complete balanced fertiliser to the soil at the start of autumn will boost the soil fertility to ensure healthy growth. Additional fertiliser may be applied every 6-8 weeks, but should be stopped immediately when the head starts forming.

Don’t use liquid fertilisers, they wash out very quickly, and are only meant to be used to provide a supplemental or additional feed every few weeks after the slow-release fertilisers are used.

5. Over-fertilising

Applying too much fertiliser can lead to an excess of nitrogen, which will force the plant to produce prolific leaf growth, possibly at the expense of head formation. Avoid fertilising cabbages while the head is forming, as this may cause excessive leaf growth and splitting of the head.

6. Pest Damage

If the central growing point of a young cabbage plant is damaged by pests, the existing leaves in the middle of the plant will thicken and harden, and no additional leaf growth will be produced in that portion of the plant, preventing the formation of a head. For this reason, it’s important to protect young plants from pests (such as cabbage white butterflies and snails) and frosty weather, and to also be careful when handling them so as not to damage them.

7. Overcrowding

Cabbages should not be planted too close together as this may prevent them forming heads, Give them plenty of room to grow!

Depending on the variety of cabbage, the space between plants and the space between rows may vary, as larger cabbages will require much more space than the dwarf varieties. The spacing is usually specified on seedling punnet labels and seed packaging, and typically cabbages are spaced 30 – 45cm (12 – 18”) apart, with rows spaced 60cm (24”) apart.

As we can see from the factors listed above, improper growing conditions which stress cabbage plants or stunt their growth during their growing period can cause the plants to not form heads. This would be considered a crop failure when growing cabbages, as the head is the edible part of the plant.

Cabbages will produce a reliable crop if we plant them at the correct time of year, ensure that their growing requirements are met, protect them from pests and frost damage when they’re first planted, and allow them enough time to mature. Nature will do the rest!

References

1. Texas AgriLife Extension Service, Texas A&M System – Cabbage
2. University of Arizona, Yuma County Cooperative Extension – Green Cabbage by Kurt Nolte
3. University of Minnesota Extension, Growing cabbage in home gardens
4. Penn State University, PlantVillage – Cabbage (red, white, Savoy), Diseases and Pests
5. University of Florida, Institute of Food & Agricultural Sciences (IFAS) – Gardening Solutions, Cabbage
6. University of Maryland Extension, Home and Garden Information Center – Cabbage