Gadenin日本語Get the appThe difference from round radishes is depth
Timing, row sowing, covering the seed and keeping it moist until it sprouts are all the same as for the round red radish. What changes is that the long white root drives 2 to 6 in (5 to 15 cm) into the ground. A round radish is happy with 4 in (10 cm) of loose soil; a long one that hits a stone or a hard layer below that bends, forks or scars its white skin.
Beds along a house foundation or a front walk often hide construction gravel and concrete chips below clean-looking topsoil. Push a spade in 6 to 8 in (15 to 20 cm) and see what comes up before you sow.
- Dig 6 to 8 in (15 to 20 cm) deep Two weeks before sowing, turn the soil to the depth of a spade blade. White Icicle wants the full 8 in (20 cm); Shirahime and the short Shironaga type are fine with 6 in (15 cm).
- Remove stones and hard lumps Break up the turned soil and pull out pebbles, root pieces and compacted clods. Even a half-inch stone will deflect a root tip. You do not need to sift, just crumble it until it breaks apart in your hand.
- Mix in lime and compost Rake in garden lime at about 3 oz per square yard (100 g per square meter), wait a week, then work in 4 lb (2 kg) of finished compost and a small handful of balanced fertilizer through the whole depth. Unfinished compost lumps cause forked roots, so use only well-rotted material.
Raise the bed and size it by rows
Because the root goes deep, poor drainage rots it from the tip. In the garden, mound the soil into a bed about 4 in (10 cm) high so rain does not pool. A single row needs a bed 12 in (30 cm) wide; two rows need 20 in (50 cm) with 6 in (15 cm) between rows.
| Layout | Bed width | Row spacing | Good for |
|---|---|---|---|
| One row | 12 in (30 cm) | None | A narrow strip by the front door or a path edge |
| Two rows | 20 in (50 cm) | 6 in (15 cm) | A small garden bed, enough for a family |
| Planter | 26 in long, 8 in deep or more (65 x 20 cm) | Two rows 6 in apart | Balcony, Shirahime or the short Shironaga type |
A shallow planter makes the root hit bottom and curl. Use 8 in (20 cm) of depth for Shirahime and Shironaga, and at least 10 in (25 cm) for White Icicle.
Sow in a row, one seed every half inch
Sow in drills just like round radishes. Press a board edge or a stake into the soil to make a furrow 0.4 in (1 cm) deep and drop one seed every 0.4 in (1 cm). Long white radishes grow bigger tops than round ones, and you will thin to 2 to 2.5 in (5 to 6 cm) in the end, so do not sow thicker than that.
- Furrow 0.4 in (1 cm) deep The Japanese packet instructions call for 0.4 in of cover and at least 0.4 in between seeds. Too deep and germination is ragged; too shallow and rain washes the seed out.
- Cover and press with your palm Pinch the soil from both sides of the furrow over the seed and press lightly with your palm so seed and soil touch. Pressing lets water reach the seed and evens up emergence.
- Water with a fine rose Right after sowing, water generously with a watering can fitted with a fine rose so the seed does not move. Until sprouts show, water again whenever the surface starts to whiten.
- Cover with insect netting the same day Flea beetles love the first seed leaves and can stop a seedling cold. The day you sow, lay fine insect netting (mesh under 1 mm) directly over the bed and bury the edges.
Sprouts in three to five days
In the right temperatures the seed leaves appear in three to five days. Most failures at this stage come from overwatering: soil that stays wet rots the seed or the new root. Keep it just moist, and once the seed leaves open, water less often.
- A gap in the row Either it dried out, the cover was too deep, or birds took the seed. If nothing shows after a week, recut that section of furrow and resow.
- Leggy, flopping seedlings Not enough light, or sown too thick. Make sure the netted bed gets full sun, and pull crowded seedlings to 0.4 in (1 cm) apart while they are still at the seed-leaf stage.
How an early-fall sowing proceeds
Sown in early fall in a mild climate, the crop grows into cooling weather, so everything takes a little longer than a spring sowing. Expect sprouts in three to five days, the first thinning at two true leaves, the second at four to five, shoulders showing around six weeks, and harvest from about week seven. Growth slows visibly once daytime highs drop below the mid 60s F (about 18 C), so judge by the plant, not the calendar.
| Days from sowing | What you see | What to do |
|---|---|---|
| Day 0 | Sowing | Deep dig, furrow, 0.4 in cover, netting on |
| Days 3 to 5 | Seed leaves open | Water only when the surface dries; peek under the net |
| Days 10 to 14 | Two true leaves | First thinning to 1.2 in (3 cm) |
| Days 20 to 25 | Four or five true leaves | Second thinning to 2 to 2.5 in (5 to 6 cm), light feed, hill soil to the crowns |
| Days 30 to 40 | Shoulders 0.8 in (2 cm) above soil | Pull one to check length, then harvest the largest |
| Days 45 to 55 | Late fall | Finish harvesting before hard frost |
Sow later than early fall and harvest slides into frost. Even in a mild climate, make early fall the last long-radish sowing, or cover later sowings with floating row cover.
Resowing, and how spring differs
If a fall sowing fails, resow in spring once the soil warms. Spring crops grow into rising temperatures and finish faster, but as days lengthen they bolt more readily and the pests multiply. Fall gives sweeter, straighter roots and fewer bugs; spring gives speed. Knowing that helps you pick the next sowing date.
- Spring: sow once soil passes 50 F (10 C) A floating row cover evens out germination, and the first roots come about four weeks later. Sowings after late spring run a real risk of bolting.
- Do not sow in summer In the heat of summer the plants bolt before the root fills out, and flea beetle pressure peaks. Skip summer and start again in early fall.
- Sow a little every two weeks Sow the whole packet at once and everything matures together and gets past its prime. One short row every two weeks through early fall keeps you in radishes until frost.