Everything you need to know about growing Napa cabbage
Find a video version of this growing guide on my YouTube channel HERE.
Napa cabbage is an easy crop especially for beginner gardeners. You get fast results as typically they are ready for harvest in about 2.5-3 months from seed. I recommend that you grow Napa cabbages to get the hang of growing cabbages in general, and then try the bigger heading types like savoy or red cabbage.
There is so much that you can do with cabbage. They can be steamed, added into stir-fry's and soups or preserve by making kimchi.
Cultivar Selection
⦁ Color - colors range from green to more light greenish yellow. There are some hybrid cultivars that are purple/red.
⦁ Leaf shape - some are more loose leaf open types "Kogane", while others are more barrel shaped with upright heads like "Matsushima No. 2". This is like the standard ones you will find in the grocery store. Some also have tall cone shapes.
Sowing seeds or Transplanting
⦁ Direct Sowing Method - Direct sow after your average last frost date has passed. Or as another guide, direct sow once your average monthly maximum temperature is 85F or below. As an example, in my garden this is the months of October thru March. You can find your monthly average minimum and maximum temperatures from www.plantmaps.com.
⦁ When I direct sow them, I loosen up the soil surface, mix in some blood meal, scratch seeds into the soil surface, barely cover with soil, keep moist until they germinate in about 3-5 days.
⦁ Spacing - I highly recommend square foot gardening guidelines and plant 1 foot apart. They get very big.
⦁ Transplant Method - Transplant into the garden 12 weeks before your first frost date or once maximum average temperatures fall below 85F. Add a handful of blood meal into the planting hole.
⦁ Sowing indoors - If you prefer to get a head start on the season, start them in small seed trays (I use the 72 cell seed trays) about 6-8 weeks before the target date you want to transplant them into the garden. Using my garden as an example, I start seeds in doors at the end of August/early September with the goal to transplant into my garden in October. If seedlings are exposed to too much heat, it will stunt their growth and they might not ever recover. Therefore, I recommend to start them in doors only.
Sun Requirements
6 hours of full sun is best. My plants are happiest with afternoon shade. Too much sun can cause leaf burning, or too much heat will promote bolting. Bolting is when the plant decides its the end of their life cycle and they need to flower to produce seeds.
Soil Requirements
Light fluffy soil with organic material/compost. They can grow well in containers or grow bags as they have shallow root systems.
Water Requirements
Cabbages are 90% water, so they like water but not sitting in wet soil for a long time (which promotes root rot). Water when the soil feels dry about an inch or two down. Regular watering will help to encourage growth and to prevent bolting.
Optimal Growing Temperatures
Napa cabbages grow best with average temperatures are 50-80°F. Check out www.plantmaps.com to find your average minimum/max temperatures per month. They struggle once temperatures go over 80F. Using my garden as an example, November through March is when max temperatures stay under 80F. They can survive a light frost, but can get damaged at temperatures 26F and below.
Succession sow new seeds every 4 weeks to keep the supply going.
Growth Habit
This depends on the cultivar. They get huge, like a rosette shape. Bottom leaves lay flat to collect sun light while the head forms in the middle.
Pruning
Remove dead, old, diseased leaves when ever possible to prevent spread and deter pests.
Fertilizing
A good application of blood meal at the beginning is great. They need lots of nitrogen to promote leafy green growth. I like to sprinkle some organic granular fertilizer half way thru its growth (around 1.5 months in the ground), to give them a final boost.
Pests
You will get worms so be prepared. The leaves will look munched on or you will find small orange/green/black balls on the leaves (worm eggs and poop). You probably wont find the worms because they tend to be nocturnal. Spray with BT (bacillus thurigensis) or Spinosad. Both are considered organic.
Slugs - use beer traps and sprinkle diatomaceous earth around the base of the plants.
Aphids - usually this is an ant problem. Treat the ants with green spike ant traps. Make a spray with need oil or strong smelling essential oils like peppermint or rosemary. Plant a lot of trap crops like sunflowers and nasturtiums.
Diseases
Leaf diseases are usually caused by poor air circulation. The leaves cannot dry off quickly which creates a breeding ground for pathogens. You might get powdery mildew, blight, or yellow spots. I treat all leaf diseases with 1 cup of hydrogen peroxide (3%) per gallon of water.
Harvest
You can start harvesting baby leaves. However, if you you want to harvest a large head, the plant will need its leaves to gather energy to output a huge head. You want to find the sweet spot where the head is as big as possible but before the plant starts to bolt. I find that is around the 3 month mark. Cut at the base, leave the roots in the soil. If your not going to use them right away, set the bottom in a dish with water. Or rinse them off, allow the leaves to dry, and then refrigerate. They will last around 2 weeks in the fridge.