Watering Indigo Plants: Information On True Indigo Water Needs

By: Mary Ellen Ellis

Indigo is one of the oldest cultivated plants, used for centuries and longer to make a beautiful blue dye. Whether you are growing indigo in your garden to make the dye or just to enjoy the pretty pink flowers and shrub growth habit, indigo irrigation requirements are important to understand to help it thrive.

About True Indigo Water Needs

There are false indigo plants, but true indigo is Indigofera tinctoria. It grows best and as a perennial in zones 9 and up; in colder areas you can grow it as an annual. Indigo is a small or medium shrub, growing to about five feet (1.5 m.) tall. You can trim it to shape into a pretty flowering shrub that produces pinkish purple blooms. The dye comes from the leaves.

Indigo plant watering is important to consider, not just for the shrub to grow well and thrive, but also for dye production. Make sure your plant gets enough water and at the right frequency for it to be healthy but pay particular attention to water if you are going to be the harvesting leaves for dye.

How to Water Indigo Plants

If you are not harvesting leaves to make dye, watering needs for indigo are pretty simple. In fact, when you have a well-established plant, it will be pretty tough in the face of drought. Begin by watering every couple of days in the growing season to get your shrub established. The ideal conditions for the soil are evenly moist, so don’t let it dry out too much. And, be sure the soil drains well. You can water less in the winter.

Watering indigo plants becomes more important if you are making dye. Studies have shown that the frequency of watering can impact how much dye you get from an indigo plant. For instance, yields of dye were higher when indigo bushes were watered every one week as compared to irrigating every two weeks. Yield was also found to be higher when watering stopped one week before harvesting the leaves as compared to ten days or longer.

If you are growing indigo to enjoy a pretty shrub, water regularly in the growing season until it is established and after that only when it hasn’t rained a lot. For harvesting dye, even when established, continue to water your indigo at least once a week.

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MSU Extension Gardening in Michigan

Planning a water-smart garden begins with understanding your site. Our Great Lakes landscape was carved out by glaciers leaving behind many different types of growing environments. Soils range from dense clay to gravelly sand that are distributed across the native terrain. Home gardens that begin with a soil test can be designed around the existing pH, soil type and texture. Visit the MSU Soil Test website to order your soil test today.

Understanding the water-holding capacity of your soil and the water needs of each plant type is the next step in creating your water-smart design. Incorporate organic matter such as compost or leaf mold into droughty soils and employ the qualities of water-holding mulches around beds or plants that are sited in these soils. When using organic mulches, take care to break up the top “crust” once a season. Mulches such as hardwood bark or pine fines may become overly dry, making it difficult to re-wet, hence working against the garden instead of for it.

Thirst not: Choose the right plants

Plants with low moisture requirements are a gardener’s first defense against tough, dry sites. Many native, woody trees and shrubs are highly adaptable to the urban landscape as well. For example, understory shrubs such as bottle-brush buckeye or our native diervilla can compete with surrounding plants and survive a dry summer. Group these types of shrubs with upland tree species such as the bur oak that can easily tolerate “feast or famine” conditions. Ideas for additional native woody plants can be obtained in the Smart Gardening tip sheet titled “Drought-tolerant plants save water, money and time.”

Perennials that have silvery foliage such as catmint (Nepeta sp.), Russian sage (Perovskia) and yarrow (Achillea) ‘Moonshine’ are wise choices for areas that are droughty. Another group of succulent plants known as stonecrop (Sedum) provide a wide variety of colors, textures, heights and even low, ground-hugging habits. Splashes of color from bulbs can make a landscape plan exciting and add seasonal interest. Ornamental onion (Allium), many types of lilies and even tulips are great choices for a dry, sunny site.

Low-growing sedum like this ‘Angelina’ paired with an ornamental grass, pennisetum ‘Burgundy Bunny’ is thrifty as well as beautiful. Photo credit: Rebecca Finneran

Deeply rooted plants with native parentage such as false indigo (Baptisia), cup plant (Silphium) and goldenrod (Solidago) are also a great addition to a water-wise garden.

Get smart – be intentional!

During the design phase, plan to group plants with “like needs” together. If you are planning on using plants that require supplemental irrigation, fertilizer and nutrients, intentionally plant these together and to prevent your own frustration, plant them relatively close to a water source.

Shade-loving hostas, big-leaved ligularia, sedges and lungwort tend to be “thirsty” perennials. Even in dense shade, most of them will wilt or yellow out during the long days of summer. Several plants like Japanese painted fern use dormancy as a defense mechanism, but quickly re-sprout when late-summer rains occur. Instead of eliminating these plants from your choices, plan to group them where you can concentrate your irrigation efforts.

Grouping plants such as Japanese forest grass and coral bells beneath shallow-rooted trees creates an environment where both can grow successfully. Photo credit: Rebecca Finneran

If you have droughty, full sun areas in the landscape, match plants to that space. Using graph paper, define existing conditions by sketching circles to indicate the edge of a shady spot, excessively dry area, etc., where you can begin to group your plants according to their needs.

Consider alternatives to traditional turf grasses. Do we really need that palatial expanse of lawn? We care about our lawns, but evaluate how much lawn is really necessary to the overall design. Turfgrass requires a fairly high level of care including supplemental water (at times) and fertilizer. Large areas of lawn can be replaced with low-growing, rugged native grasses such as prairie dropseed (Sporobolus) or different types of sedge (Carex.) Mowing once a season would be fine for these plants that do not require any additional inputs.

Replacing lawn with expanses plants including tough natives at the water’s edge not only cuts down on watering and mowing, but also prevents run-off and sediment from entering the waterway.” Photo credit: Rebecca Finneran

When it rains…Does it pour?

When you need to irrigate, plan to evaluate the efficiency and output of your sprinklers. Automatic watering systems can supply an excessive amount of water as well as cause the need for supplemental fertilization for some plants. Common sprinkler devices also may not apply an even spray of water, so be sure to check out the pattern to see where it is heavy or light. For more information, consult the Smart Gardening tip sheet titled "Smart watering for lawns: Don’t let the lawn squeeze you dry."

Remember to group plants that have a high need for water near a source. Photo credit: Rebecca Finneran

Lastly, buy a rain gauge! If you know how much rain fell while you were sleeping, you will be much better at determining the needs of your garden plants when you are awake.

For more information on a wide variety of smart gardening articles, or to find out about smart gardening classes and events, visit the Gardening in Michigan website.

Sources for Baptisias

Quality garden centers carry a variety of baptisias, generally in larger sizes than can be obtained through mail order. The mail order sources listed below stock several hard-to-find baptisias.

Niche Gardens
1111 Dawson Road, Chapel Hill, NC 27516
(919) 967-0078

Plant Delights Nursery, Inc.
9241 Sauls Road
Raleigh, NC 27603
(919) 772-4794

1128 Colleton Avenue
Aiken, SC 29801
(803) 648-7522

If this document didn’t answer your questions, please contact HGIC at [email protected] or 1-888-656-9988.


Karen Russ, Former HGIC Horticulture Specialist, Clemson University

This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.

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