Gadenin日本語Get the appPlant into a trench so you can backfill later
The white part of a Welsh onion is simply the part that has been kept in the dark. You cannot add length to it later unless you left yourself room to bury more stem, so the trench is the whole point of the planting method. Dig a trench four to six inches (10 to 15 cm) deep and about six inches wide, and set the plants in the bottom of it rather than on the flat.
Backfill only enough to cover the roots and about an inch of the base, roughly two inches (5 cm) of soil in total. The rest of the trench stays open. Over the following months you fill it in gradually, and each fill adds white shank. Plant on the level instead and you are already committed to a short, mostly green plant.
On heavy clay that holds water, make the trench shallower, about three inches (8 cm), and mound the soil you pull back into low ridges beside it. A deep trench in wet clay fills with standing water and rots the crowns.
Spacing, and the difference between singles and clumps
Plant single seedlings two inches (5 cm) apart along the trench, with trenches twelve to sixteen inches (30 to 40 cm) apart. That gap between rows is not generosity, it is the soil you are going to shovel back in later, so it needs to be there.
Plant multi-sown clumps as clumps, eight to ten inches (20 to 25 cm) apart, and do not tease them apart. Each clump swells outward year on year and becomes the unit you cut from and later divide. Clumps are the better choice for a permanent bed, singles for a row you intend to lift and use within one season.
| Planting unit | In row spacing | Between rows | Best for |
|---|---|---|---|
| Single seedlings | Two inches (5 cm) | Twelve to sixteen inches (30 to 40 cm) | One season rows, long straight shanks |
| Multi-sown clumps | Eight to ten inches (20 to 25 cm) | Fourteen inches (35 cm) | A permanent perennial bed |
| Divisions from an old clump | Six inches (15 cm) | Fourteen inches (35 cm) | Fast fill, cutting within two months |
| Rooted supermarket bases | Three inches (8 cm) | Twelve inches (30 cm) | A quick free row, no long term plan |
Soil, and the one thing to get right before you dig
This crop stays in the same ground for three or four years, so anything you fail to add now you will be adding as a top dressing forever. Work in a bucket of well rotted compost per square yard and lime acid soil up towards a pH of 6.5 if it sits below 6.0. Fresh manure is a mistake here because it drives soft, thick, watery growth that rots at the base over winter.
Full sun is best but this plant tolerates half a day of shade better than any bulbing onion does, because it is not trying to fill a bulb before the days shorten. What it will not tolerate is standing water. If your bed puddles after rain, raise it four inches (10 cm) before you plant rather than after.
Setting the plants and the first three weeks
The failure people report most often is that nothing seemed to happen for a month. That is usually success, not failure. Welsh onions put roots down before they put leaf up, and a plant that sat still for four weeks then started growing is behaving exactly as it should.
- Trim the roots and tops Shorten straggling roots to about an inch (2.5 cm) and cut the leaves back to five or six inches (13 to 15 cm). It sounds brutal and it is standard practice. It cuts water loss while the roots are not working yet.
- Set them upright against the trench wall Stand each plant or clump against the vertical side of the trench and push soil back against it. Leaning the plants makes crooked shanks that never straighten out.
- Firm gently, then water in Press the soil against the roots with your fingers, not your heel, then water so the soil settles around them. Heavy treading on the trench floor compacts it and the roots stall.
- Then leave them dry for ten days After that first watering, hold back unless the soil goes bone dry. Alliums root down in search of water, and constant surface watering keeps the roots shallow.
- Expect a yellow fortnight The outer leaves go yellow and collapse within a week or two. This is normal after transplanting. New growth appears from the center in two to three weeks, and that is your sign the plant has taken.
Rooting a bunch bought for the kitchen
A bunch of scallions sold with the roots still attached will grow. Cut the tops off about two inches (5 cm) above the roots, keep the pieces you cut for cooking, and plant the bases straight into a trench three inches (8 cm) apart with the cut ends just above the surface. Standing them in a glass of water first works but produces weak white water roots, so plant them within a few days if you do.
Understand what you are getting. These bases regrow twice, sometimes three times, then thin out and run to flower, because they are already mature plants that were grown hard for market. Treat them as a free extra row rather than the foundation of a permanent bed, and raise your real stock from seed or from divisions alongside them.