indigo

Gardening Blues: Growing Japanese Indigo

by Donna Druchunas
photos by Dominic Cotignola

Click here for a recipe to dye with fresh Japanese Indigo leaves

Blue Dyes from my Garden?

When I started my dye garden, I thought I would have to stick with plants that yield yellows, tans and shades of orange. While many plants contain indigo-blue pigment, most are hard to find or unsuitable for gardening in my Colorado location. The season here is too short for growing the "classic" Indigo varieties native to India and Asia (Indigofera tinctoria), and Mexico and the Caribbean islands (Indigofera suffruticosa). European Woad (Isatis tinctoria) is easy to find and well suited to a temperate climate, but it is classified as a noxious weed in much of North America. I assumed blues were out of my reach.

After reading several natural dye books and searching on the Internet, I finally discovered Japanese indigo (Polygonum tinctorium). Also called "Dyer's Knotweed", this member of the buckwheat family has been used as a source of blue dyes in Japan and Southeast Asia for centuries. I ordered a packet of seeds and planted a whole flat. The books I'd read said Japanese indigo is very easy to grow and should be planted in full sun. I transplanted a few seedlings into my flower bed. They died. I planted a few more in my herb garden. They died. I spread the rest around my yard and waited. After four months, all I had to show for my effort was five lonely, but hardy, plants.

It was enough to dye a few small skeins of wool - and enough to whet my appetite. Determined to get a full-crop, I've adapted some simple techniques from my vegetable garden for growing Japanese indigo and have successfully raised a full bed of bushy plants, without losing any seedlings. If you take time to nurture your seedlings, you will be rewarded with healthy plants that yield clear blue dye - and youll have much more fun than you would using purchased indigo.

Good Beginnings

Sow the seeds indoors in early Spring, six to eight weeks before the last frost for your area. Plant the seeds in plastic six-pack planters or 5 cm (2 in.) plastic pots. Don't bury the small seeds too deeply, just sprinkle a little soil over the top. If you don't use a pre-fertilized seed starting mixture, apply fish emulsion fertilizer every two weeks.

Use a seed-starting heater to keep the soil warm until the seedlings sprout (or keep the pots on top of your computer monitor until they sprout, but be careful not to over water them here). This might take a few weeks, so be patient.

Figure 1: New Seedlings in Pots

Cover the flat with plastic wrap until the seedlings sprout to keep the moisture from evaporating. Use a mister at first so you don't flood the pots or crush the tiny plants. Once the seedlings sprout, you may need to water them two or three times a day. Don't let the seedlings wilt, or the leaves turn blue and dry out. Unlike most other plants, Japanese indigo will not recover after it wilts.

Building a Healthy Home

The key to transplanting Japanese indigo into the garden is understanding the environment it needs: just the right amount of sun, warm temperatures, fertile soil and lots of water. The possibility of late frosts in Northern and high-altitude gardens combined with the recent drought in much of Western North America, pose a particularly thorny challenge. To overcome these obstacles, you need to prepare your garden carefully.

First, choose a location with lots of sun. If you live at high altitude, partial afternoon shade will keep the seedlings from drying out or getting scorched on hot Summer days. I planted mine under a young tree.

If you can, use a raised bed design for your garden. The soil of a raised bed warms up faster, and lets you transplant Japanese indigo seedlings several weeks earlier than in a regular garden plot without risking frost damage. I took the easy route and bought a house that had a beautiful raised-bed garden in the back yard. If you are not so lucky, you can make a simple raised bed by raking the garden soil into a ridge 10 to 20cm (4 to 8 in.) high away from the foot paths. Frame the new bed with landscape timbers, concrete blocks, bricks, or aged railroad ties. (Old railroad ties are okay, but new ties may cause some creosote damage to plants.)

Amending soil with organic matter is the most important step in preparing any garden, and you will get better blues from your Japanese indigo plants if they are planted in rich soil. If you have an established bed, just work in some compost and aged manure (high amonia levels in fresh manure can harm plants) a few weeks before you plan to put out your transplants. If you are building up a new bed, you should aerate the soil to a depth of about 60cm (24 in.). Traditional double-digging is done with a spade, but fankly I would never get around to such back-breaking work. Instead, I bought my husband a roto-tiller.

For thirsty plants like Japanese indigo, drip irrigation is the most efficient way to deliver water where the plants need it most: the root zone. I use inexpensive soaker hoses, made from recycled tires. To install a soaker hose, make furrows the length of the bed, arrange the hose along the tops of the furrows, and bury it under a layer of mulch to help reduce evaporation. Fasten the hose to the soil with 20cm (8 in.) pieces of wire. (These are available pre-cut and shaped at most garden centers.)

Figure 2: Drip Irrigation Saves Water

Test the drip system for a week or so until you determine the correct timing for your garden and soil conditions. When you have particularly hot or dry weather, you may need to water twice a day to keep the plants from wilting.

To further protect Japanese indigo from the elements, you can build a hoop house. Basically an unheated tunnel made of plastic, a hoop house warms the soil in Spring, substitutes as a cold-frame, and eliminates the need for protecting individual plants with "walls-of-water" or other types of cloches.

Figure 3: Setting up a Hoop House

A hoop house takes about an hour to put up, and you only need a few inexpensive items that are readily available at most hardware or home-improvement stores:

8 pieces of rebar (steel reinforcement bar) 46 cm (18 in.) long - optional
4 pieces of 2.5cm (1 in.) PVC pipe 3 meters (10 ft.) long
7.6 meters (25 ft.) of nylon cord
1 sheet of heavy plastic 3.5 x 6 meters (12 x 20 ft.)
A few rocks or bricks

Setting it up is easy:

1. On each long side of the bed at 1.2 meter (4 ft.) intervals, drive four of the rebar stakes into the ground leaving 15cm (6 in.)exposed.

2. Fit the PVC pipe sections over the rebar stakes to form arches that reach across the bed.

3. Tip: If you have soft soil, you can drive the PVC pipe directly into the soil without the rebar stakes.

4. Run the nylon cord across the top of the hoops, wrapping it around the top of each hoop, and tying it firmly to the first and last hoops. This will stabilize the hoop house in the wind, and keep the plastic from caving in on the plants in a rain or hail storm.

5. Cover the arches with the plastic sheeting, anchoring it along the ground with bricks or rocks. Leave enough plastic at each end to fold together and clip shut at night. During the day, leave the ends open to vent the hoop house so the plants dont overheat.

The plastic cover makes the hoop house into a mini-greenhouse and keeps in heat and moisture. When the plants stand up straight, have ample new growth, and the leaves darken to a rich green with a slight blue tint, remove the plastic covering. If you live at high altitude, cover the frame with shade cloth to protect the plants from being scorched by the afternoon sun. In the Fall, replace the plastic to extend the season.

All of this preparation takes a little time and effort but makes the difference between success and failure.

Moving In

The seedlings can be transplanted into the garden bed when they are about 15cm (6 in.) tall.

Figure 4: Seedlings are Ready to Transplant

Before you transplant them into the garden, make sure you harden them off thoroughly. A week after the average last Spring frost for your area, start putting the seedlings outside in a shady area for an hour or two a day. Slowly increase the time until, after a week, you can leave the seedlings outside over night. Don't leave them in full sun or they will quickly dry out, the leaves will shrivel, and the plants will die.

Soak the soil before you plant the seedlings. Be very careful not to disturb the roots of the seedlings as you remove them from their pots. If necessary, cut away part of the pot and plant the whole thing in the ground. The joints in the stems will go into the ground outside of the pot and will grow additional roots.

Figure 5: Don't Disturb the Roots!

Maintenance

The hard part is over! About a week or two after you set out the plants, give them one foliar application (apply fertilizer to the leaves) with fish emulsion, following the manufacturer's instructions, then fertilize once a month with fish emulsion using your drip irrigation system or a watering can.

Japanese indigo does not have many problems with pests and diseases once established. Most pests don't like the taste of the leaves, but I have seen grashoppers munching on young plants. If you do spot any pests, use insecticidal soap or just pick off the pests with your fingers. While it's safe enough to use pesticides because you wont be eating the plants, I try to avoid using chemicals in my garden whenever possible.

Ready to Harvest

When the plants are about 30cm (12 in.) tall, probably in July, they are ready to harvest. Starting at the base of the stems, pick the leaves when you are ready to dye. You can pick up to about one-third of the leaves, and the plants will re-grow quickly. By harvesting leaves every week or two, you can get several dye baths in a single season.

Figure 6: Ready to Harvest

You can also save your own seeds for future plantings. Bring a few plants or flower cuttings into the house if you have a short growing season.

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