Persicaria tinctoria is a native to Vietnam and Southern China and is frost sensitive. It is mostly grown as an annual and though more demanding than Woad it is worth growing. Persicaria tinctoria yields more colour for the same weight of Woad leaves. Though not as high as Isatis tinctoria, it has a relatively high indacatin content. It grows fast and can usually be harvested six weeks after planting in the right conditions giving two harvests in our climate.
I’ve grown my first crop of Japanese indigo this year having been given a plant by my good friend, weaver and natural dyer Jane Meredith last year which flowered and gave me enough seed for this year. I plant seed in trays on a sunny window sill in April. They germinate readily in a couple of weeks and are ready to be planted out after the last frosts in late May.
I planted my precious seedlings ( around 50) in large pots of rich manure compost and some in the ground. I was hedging my bets because of years of bad summers. I put some pots in a friends poly tunnel some in my garden and the rest in my vegetable/dye garden. Of course we have since had a lovely warm summer and two harvests of indigo. However, the plants in the open and in the ground though not as large produced lots of indicatin rich leaves compared to those in pots which were leggier I think. It is important to make sure your ground has plenty of rich compost and is well watered once a week or daily in pots.
The plants are ready to harvest after about six weeks and you can see when they are ready by picking a leaf and drying it. If it dries and turns dark blue it is ready to harvest. I had two harvests of indigo, one in mid August and the second at the end of September. The leaves were dried in the sun and then stripped from the stems. The crisp dried leaves were put into old pillowcases to be stored in a dry and dark place ready to compost and make into Sukumo (Japanese indigo balls). I don’t think I have enough to make it worth while this year though.
I left 3 pots and didn’t harvest leaves from them so that they would flower. Once they have been pollinated and you can be sure of seed I cut off the flower heads and put them in paper bags hung in my warm kitchen. I then have seed ready for next spring with enough to give to friends. I will also bring in a plant to overwinter.
For growing on a large scale look at Rowland Ricketts, Indigrowingblue.
Dyeing using fresh leaves
The first vat uses only leaves, cold water and a little white vinegar. You have to plan your dyeing session as the leaves need to be processed quickly after harvesting.
Pick a bucketful of stems and leaves. Strip the leaves and put the them in iced cold water. Place batches in a blender or food processor cover with the ice cold water and blend. Pour contents into a bucket and add 50ml of white vinegar to approx 20l of water. This will help release pigment and prevent it’s breakdown. Squeeze the leaves to help release their pigment and then strain through a sieve. I use muslin in the sieve which also makes it easier to squeeze the green liquid out of the leaves. Put the pulp back in the orriginal bucket with more cold water and vinegar and repeat the process.
Place your silk in the dye and move around for about an hour. The white silk will turn green then turquoise and then blue. Squeeze open to the air to oxidise and then rinse under running water. Repeat to get deeper shades. Save the liquid and pulp to use in a conventional vat using a standard recipe.
Put pulp and spent cold vat into a pan and heat very gently over 2 hours to 50C then strain and squeeze again through muslin. Add bicarbonate soda a tablespoon at a time until the bath reaches ph9 testing with litmus paper. Then add 2tsp sodium hydrosulphite and leave covered in a warm place for an hour.
Place previously soaked wool ( in a similar temperature water bath) in the vat and move gently for 10 minutes. Rinse again in warm water and oxidise for 15 minutes. Return to the vat for shorter dips to deepen colour. Finally rinse in a vinegar bath to neutralise the alkalinity,
Now India Flint has posted a tip. put fresh leaves in a freezer bag and freeze for at least an hour and then crush them into luke warm water and leave cloth overnight to absorb colour. Haven’t tried this but will freeze any remaining leaves to try this method
My aim is to make my own fermentation vat using indigo I have grown. I will keep you posted!
I bundled some leaves in silk and steamed the bundle for about an hour. Initially there was no sign of colour which was expected as indigo isn’t supposed to respond to extreme heat. Three days later, however, colour suddenly started appearing. Magical!