There Are Three Common Reasons Your Cabbage Plants Aren't Forming a Head

I've been growing cabbages for years, and there have been so many times when they never quite turn out the way I was hoping. I'll end up with a lot of leaves, sure, but not necessarily that nice, tight head with layer upon layer of tender little leaves inside that I was expecting.

I planted about 20 Napa cabbages in my garden one year so that I could see which things actually helped them form a better head. From this super-scientific experiment, I came up with three reasons cabbages delay forming a head or never form a head at all.

Cabbage Won't Form a Head If the Temperature Isn't Right

Cabbages are in the brassica family, and this is a cool-season bunch. Very few of them thrive when it's hot outside. If temperatures rise over 80 degrees F consistently, cabbage plants will either stop growing or they'll bolt (produce flowers and then go to seed).

The difficult thing about cabbage is that it also doesn't like to grow when it's too cold (below 45 degrees regularly). So, you're looking for the ideal temperature range between 45 and 80 degrees to grow cabbage under its preferred conditions. The problem is you need about 60 days in this ideal temperature range for your cabbages to grow in the garden.

For many of us, that means there's a short window of time during which cabbage plants love the weather, and outside of that window, they often just won't form a head.

Temperature Solution

You can trick cabbage into thinking it's growing under its ideal conditions a bit longer by using frost cloth on cold days and shade cloth on warmer days. Beyond that, you've got to work with the weather you've got.

Cabbage Won't Form a Head If It's Not Getting Enough Water

The next thing to keep in mind to get cabbage plants to form a head is water. A common reason why cabbage isn't forming a head is that it's not being properly watered. Water is so important for all leafy greens, really, but especially for cabbage, which is 92 percent water in its makeup. As you can imagine, any cellular growth for a plant that's mostly water will require... a lot of water.

So you really want to make sure that you're watering on the regular. Avoid over-watering, but you do want the ground to stay moist underneath these plants.

Water Solution

Use drip line irrigation on a timer to deliver consistent water to these large leafy greens just where they like it, on the soil, not the leaves.

Cabbage Won't Form a Head If It's Getting Too Much Nitrogen

We typically focus on adding nitrogen when we're growing plants for their leaves. In this case, though, if your soil is too nitrogen rich, you might get lots of leaves but not necessarily the formation of a head.

Now, don't get me wrong. All those greens that were formed thanks to the nitrogen in the soil are 100 percent edible, delicious, and nutritious. But if your goal is a compact head, then you'll have to switch up your fertilizing.

Nitrogen Solution

Add a little phosphorus-rich fertilizer like rock phosphate or bone meal. The idea here is to push more phosphorus instead of nitrogen into the roots of these cabbage plants so that the plants' focus is more on forming that nice head rather than just giving you all these greens.

Step One: Prune Your Cabbage

Once you've done a little problem solving to figure out why your cabbage plants haven't been forming a head, it's time to take a more proactive approach to encourage them to grow what you want them to. We do that through pruning.

Start by pruning those older, larger leaves on the outside of the cabbage plant. You'll be able to tell that these leaves are not really going to be part of the cabbage head because they've already opened and pushed outward.

All brassica plants push their newest growth from the heart and center of the plant. We want hundreds of little leaves forming in the centers of these cabbage plants to get a nice, tight head. When we cut back the exterior leaves, we're telling the plant to put all its energy into forming new leaves instead of making the edge leaves larger.

Bonus: If you plant intensively like I do, pruning these older leaves back will mean that there's more room in the garden for other things.

Extra bonus: Keep the leaves you're pruning because they're all edible. Bring them inside to enjoy!

Step Two: Fertilize Your Cabbage Plants

I recommend using an organic ocean-based product like Neptune's Harvest Fish and Seaweed Fertilizer. If you're shopping around for a fertilizer, just be sure to look at the three numbers (N-P-K). Remember, we don't want a lot of nitrogen (the first number).

And be sure to read the directions to get the right dosage. Just mix up your fertilizer and pour it around the base of the plants. Do this about once a week.

And That's It!

Now you're on your way to ensuring your cabbages form a head! Those heads will be ready for harvest as soon as they feel nice and firm when you give them a little squeeze. (Learn more about harvesting cabbage heads.)

Thanks for helping me bring back the kitchen garden, one cabbage plant at a time.