When to Plant Leeks
Planting Window - Start indoors + transplant
- Start indoors
- 10-12 weeks before last frost
- Transplant outdoors
- ~2 weeks before last frost
| USDA Zone | Typical Window |
|---|---|
| Zone 5 and below | Start Jan-Feb, transplant April |
| Zone 6-7 | Start January, transplant March-April |
| Zone 8 and south | Fall-through-winter crop |
Leeks are the slowest-maturing common allium on this site - 100 to 120 days from transplant - which pushes their whole timeline earlier and longer than onions or garlic, even though the crops are closely related and grown similarly in other respects.
Starting Seeds Very Early Indoors
Leek seed is typically started indoors 10-12 weeks before the last frost date, among the earliest indoor starts of any crop on this site - the seedlings themselves grow slowly and look almost grass-like for weeks before putting on real size, which can make an early start feel unproductive even though it's on a normal schedule for this particular crop.
Transplanting Outdoors
Leeks are frost-tolerant as young transplants and can go out a couple of weeks before the last frost date, planted somewhat deeper than most seedlings - often in a shallow trench that gets gradually filled in as the plant grows, which helps blanch (whiten) the lower stem, the part most prized for eating.
Summer, Fall, and Overwintering Varieties Aren't Interchangeable
Leek varieties are bred for different harvest windows - some mature faster for a summer or early fall harvest but have less cold tolerance, while dedicated overwintering varieties are bred specifically to survive hard frost in the ground and be harvested through winter and into next spring. Planting a summer variety expecting it to overwinter, or vice versa, is a mismatch that shows up as poor cold survival or a harvest window that doesn't line up with when you actually wanted leeks.
The Trenching Technique, Explained
Planting leeks a few inches deep in a narrow trench, then gradually backfilling soil around the stem as the plant grows taller over the season, blocks light from reaching the lower stem - without light, that portion of the stem stays white and tender rather than turning green and tougher, which is the entire point of the technique and the reason leeks are handled so differently from onions at planting time.
Leeks Survive a Hard Freeze in the Ground
Leeks left in the ground through a hard freeze generally survive undamaged and can be dug as needed straight through winter in many zones, which is a real practical advantage over onions and garlic, both of which need to be pulled and cured before a killing freeze.
Zone boundaries follow the USDA Plant Hardiness Zone Map (2023 revision); frost windows reflect NOAA/NCEI climate normals. Both are typical historical ranges, reviewed annually - not a forecast or a guarantee for any single year. See Methodology & Sources.
Frequently Asked Questions
Why do my leek seedlings look so thin and grass-like for so long after starting them?
That's completely normal for leeks - they genuinely grow slower and look less substantial early on than most other allium seedlings, and the visible bulking-up happens later in the season, so a leek seedling that looks unimpressive at six weeks isn't behind schedule.
Do I have to use the trench-blanching method, or can I just plant leeks normally?
Trenching is standard for maximizing the white, tender stem portion, but leeks planted at a normal, shallower depth still grow and produce edible plants - you'll just get a shorter white section and more green, slightly tougher stem, which some gardeners consider an acceptable tradeoff for less planting effort.
Can I plant summer and overwintering leek varieties together to spread my leek harvest across more of the year?
Yes - that's a common way to get more mileage out of one planting season. A summer variety gives an earlier harvest while a slower overwintering type is still bulking up nearby, and since both go into the ground around the same general transplant window, there's no extra timing complexity to growing a mix of both side by side rather than picking just one.