Gadenin日本語Get the appWhy a little at a time beats one big burial
Blanching works because the buried tissue never makes chlorophyll, stays soft and loses its harshness. But the plant has to be actively growing upward while you bury it, or you are just smothering it. Piling six inches of soil on in one go buries growing points that are not ready to climb out, and a proportion of the plants rot instead of lengthening.
The rule is simple and it is the only rule that matters: add one to two inches (2.5 to 5 cm) of soil at a time, every two to three weeks, and never cover the point where the leaves separate from the shank. Keep the soil line a good inch below that split. If you can see the V where the two outer leaves part, you have not gone too far.
Start the first earthing up about four weeks after planting, once you can see new leaf growing from the center. Earthing up a plant that has not rooted yet simply buries it.
The schedule through the season
Work with the trench you planted into first. The first two or three additions are free, they are just the soil you left piled beside the trench going back where it came from. Only once the trench is level do you start drawing soil up from between the rows into a ridge, which is why the row spacing had to be generous.
| Stage | Timing | Soil added | What you are aiming at |
|---|---|---|---|
| First | About four weeks after planting | One inch (2.5 cm) | Trench a third full, plants clearly growing |
| Second | Two to three weeks later | One to two inches (2.5 to 5 cm) | Trench two thirds full |
| Third | Two to three weeks later | Two inches (5 cm) | Trench level with the bed |
| Fourth and after | Every three weeks while growing | Two inches (5 cm) | A ridge building up the row |
| Last | Three to four weeks before cutting | None | Let the shank firm up and the soil settle |
How to actually do it without wrecking the plants
In a normal season you will do this four to six times. That sounds like a lot of visits but each one is two minutes per row with a hoe, and it is genuinely the difference between a four inch shank and a ten inch one.
- Wait for dry soil Earth up when the surface is dry and crumbly. Wet soil packed against the shank is the main cause of soft rot, and it also cakes hard and makes the shank grow crooked.
- Draw soil from both sides Pull soil up against the row from each side with a draw hoe so the ridge is even. Taking it all from one side undercuts the roots on that side and the row leans.
- Keep soil out of the leaf joint Hold the leaves together with one hand while you draw soil up with the other. Grit that falls into the joint between leaves stays there until you eat it, and no amount of washing gets it all out.
- Do not firm the ridge Leave the added soil loose. A packed ridge sheds rain sideways, keeps the shank wet at the base and makes lifting harder.
- Stop three to four weeks before you cut The last inches of shank need a few weeks in the dark to blanch properly and firm up. Soil added in the final fortnight adds nothing but dirt.
Alternatives when soil will not work
In containers, in very heavy clay, or on a bed you cannot spare soil from, blanch with a collar instead. Slip a tube of stiff paper, cardboard or a length of pipe cut down one side around the clump and raise it as the plant grows. It gives a cleaner shank with no grit in the joints, and it is the only workable method in a pot where there is no spare depth.
Straw and dry leaves work too, packed loosely around the shank and topped up the same way. They stay drier than soil against the stem, which suits a wet climate, but they harbor slugs, so check under the mulch every couple of weeks and pull it back for a day if the shanks feel slimy.
Whatever you blanch with, the shank finishes tender but fragile. Blanched tissue bruises easily and does not store well, so cut what you are going to use rather than harvesting the whole row in advance.
Keeping a record that pays off next year
Write down the date of each earthing up and roughly how much soil went on. At the end of the season, measure the white shank on a few plants and put that beside the list of dates. Two seasons of that tells you exactly how many additions your soil and your climate need, which is a number nobody else can give you.
Note the failures as well. If a patch rotted, record where it was and what the weather was doing that week. Rot from earthing up almost always clusters in the same low corner of a bed, and once you have seen it twice you either drain that corner or plant something else there.