Why do leek stems stay thin?

For years I struggled with the skinny leeks until I finally figured out to grow them. Environmental stress is usually indicated by skinny stems or spindliness, and it usually occurs from one of three things: low feeding, root-bound, or not enough light. If you address these, you should get stems as thick as a Sharpie.

Soil hilling results in stem girthing changes. I trench plant leeks 8 inches deep, progressively backfilling the trench - same as they blanch commercially. The stem buried in the trench etiolates which means it elongates but also gains diameter. Every month I add compost to the top of my planter which supplies nutrients to the stem without crusting the soil.

There is no reason to be afraid of aggressive thinning. At 6 weeks old, I remove every other seedling, which provides 4 inches of spacing for the remaining seedlings. The seedlings I sacrifice can be harvested as gourmet microgreens. The plants that survive can grow much larger because their roots will now share the nutrients and water with only half the amount of seedlings as before.

When it comes to plant growth, light quality is more important than quantity. My shaded garden is growing stout stems now that I have full-spectrum LEDs hung 18 inches above the plants. The leeks are also fooled with a 14-hour daily cycle, grown out of their ideal conditions. I have noticed increased energy costs commensurate to the increased stem diameters, now from pencil size to the diameter of a pickle jar!

Read the full article: How to Grow Leeks: Beginner's Guide to Sweet Harvests