10 Plants That Like Grey Water (Updated)

“Gently used” water from indoor plumbing systems like bathroom sinks, showers, and washing machines is formally referred to as “grey water”. Active households produce a substantial amount of grey water each day. Though this normally enters pipes that carry it into sewage systems, where blackwater (from toilets and other sources of pathogen-rich waste) is accumulated, its flow can be redirected to meet a number of uses in the home or garden.

Recycling grey water is a fantastic way to help conserve the freshwater resources in your area. Though it may contain traces of organic matter, soaps, and salts, it can easily be filtered and treated to extend its potential for re-use. Untreated grey water can legally be used to flush toilets and irrigate the subsurface layers of your garden. In some jurisdictions, it must be treated prior to soil surface irrigation (e.g. via a drip line).

Typically rich in organic nutrients, grey water can boost the development of some types of ornamental and landscape plants, especially in arid zones or during seasonal droughts. Depending on its source, it may, however, contain compounds that sensitive or acid-loving plants are unlikely to tolerate. Note that grey water should not be used for herbaceous food plants that are intended for human consumption.

The plants listed below should benefit from toxin-free grey water. Prior to installing a grey water system for your garden, make sure to check for restrictions on its usage in your area. If any harmful effects are observed, halt its use.

1) Rosemary (Salvia rosmarinus)

Often cultivated for its fragrant and oil-rich foliage, rosemary is one of the world’s most popular herbs. This strongly scented plant is a great addition to herb gardens because it eventually grows into a moderately-sized and environmentally valuable shrub. It naturally repels a wide range of pests while attracting pollinators and beneficial insects. It is thus ideal to grow close to herbs and ornamentals that share its habitat preferences.

Known for being exceptionally hardy in semi-arid conditions, rosemary tends to be more tolerant of salts and alkaline substrates than other herbs. Its natural occurrence in many coastal areas depicts these tolerances. It is thus more likely to thrive in gardens that are irrigated with grey water, which may have high concentrations of soap and salts.

If you intend to use grey water for your rosemary shrubs, make sure it does not come in contact with the plants’ aerial features. If the leaves are contaminated with droplets of grey water, they are not safe for consumption. A subsurface irrigation system, which would prevent the water from spreading freely over topsoil, would be ideal for this species.

2) Bur oak (Quercus macrocarpa)

Oak trees typically thrive in landscapes that are irrigated with grey water, and the bur oak is no exception. This lovely, water-loving tree produces the largest acorns of any Quercus species found in the US. On average, it grows to a full height of about 98 feet (30 meters) and can live for hundreds of years in optimal environments. It favors open areas, where its canopy can easily access direct sunlight. One of its most notable features is its lengthy and drought-resistant taproot system.

Nowadays, the humble bur oak is often grown along sidewalks, in parks, and in gardens that are located in urbanized or highly-developed areas. As its roots can thrive in slightly alkaline conditions, it is ideal for landscapes receiving moisture from grey water irrigation systems. Well-draining soil is a must, however, because prolonged exposure to excess moisture can damage the roots or cause wood rot.

3) Cottonwood trees (Populus spp.)

Large trees, such as those grouped under the Populus genus, are usually the most helpful when it comes to soaking up grey water and converting its nutrients into new growth. These can be planted throughout landscapes or around farms that are frequently irrigated with potentially polluted surface waters. Notable species, which grow into enormous hardwood trees, include the eastern cottonwood (P. deltoides) and Frémont’s cottonwood (P. fremontii).

Cottonwood trees favor the moisture-rich conditions of substrates close to streams and rivers, so they are perfect for the restoration of riparian landscapes. They can be planted close to spots where stormwaters are likely to settle and where soils require the aid of large roots to remain stable. If you intend to employ a surface flooding system for treated grey water, consider adding stability to the area by cultivating these trees.

4) Eastern red cedar (Juniperus virginiana)

An evergreen conifer with a knack for repopulating disturbed landscapes, the eastern red cedar is a long-lived and ecologically important pioneer species. In the wild, its stands are often found growing in pastures, prairies, and close to abandoned farms or construction sites. Due to its tolerance for a wide range of ambient conditions, as well as its capacity for competing with many native grasses, it may occasionally be considered an invasive tree.

Though this species may be troublesome in forage-rich environments, it is suitable for parks or gardens with poor substrates and moderately alkaline conditions. Its tolerance for pH levels up to 8.0 makes it a favorable addition to sites that are irrigated with grey water. Moreover, as mature specimens of this tree may consume about 30 gallons of water per day, their demands will certainly keep your grey water system running!

5) Peach trees (Prunus persica)

Fruit-producing trees are some of the best choices for gardens, orchards, or farms that regularly receive grey water. In optimal environments, peach trees tend to be tolerant of slightly alkaline conditions, though these may impact their rate of stone fruit production. Nonetheless, their high demand for moisture makes them suitable for grey water systems with a high output rate, especially during summer.

Grey water, which is usually rich in nutrients, can boost the growth of peach trees as they require more nitrogen than many other fruit-producing plants. An inadequate supply of nutrients can stunt the growth of peach trees or cause their leaves to turn yellow. If nutrient or water shortages occur prior to the fruiting period, you can expect an unfavorable yield. This is why grey water may serve as a beneficial resource for orchards that are prone to experiencing droughts. For production-intensive peach farms, however, take note that fresh, clean water would be best.

6) Grapes (Vitis spp.)

Some fruiting vines can actually grow well in gardens that are irrigated with grey water. The common grape vine (V. vinifera) comes in many popular cultivars, some of which are suited to a variety of conditions. Note that, more often than not, they do thrive best in well-draining soils with a neutral pH. While grey water can certainly provide them with a wealth of nutrients for fruit production, it would be best to reuse it for vines only if it is free of strong alkalis and salts.

If you intend to use grey water for a patch of grape vines, make sure it is released at the subsurface level of the substrate or below a layer of mulch. This way, it is less likely to come into contact with the leaves and fruits.

It would be prudent to alternate grey water usage with generous provisions of clean freshwater. This way, any accumulated soap can be diluted. Regardless of whether grey water has come into contact with the fruits or not, it would be best to thoroughly disinfect them prior to storage and consumption.

7) Honeysuckle (Lonicera spp.)

The honeysuckle is a climbing vine with a knack for entwining the branches of shrubs and trees. As long as its roots are sheltered and regularly watered, it can spread over a considerable area and cover entire sections of a wall or building. This flowering vine is often grown in woodland gardens, where its charming blooms can attract a wealth of pollinators. The strong scent of the blooms, which is most pronounced at night, attracts moths, mice, and birds.

Honeysuckle can thrive in soils with pH levels of up to 8.0. This makes it a great candidate for ornamental gardens that receive grey water as a chief source of nutrients and moisture. As it is also fairly tolerant of salts, minimal concentrations in grey water are unlikely to damage its leaves.

These tolerances for both salt and alkali highlight its potential as a plant for phytoremediation purposes in coastal areas. Note that some Lonicera species, such as the Japanese honeysuckle (L. japonica), may be hardier in saline substrates than others.

8) Red raspberry (Rubus idaeus)

Recycled water can definitely be used as a source of moisture for fruiting shrubs. As long as the fruits don’t touch the ground, they should be fairly safe from contaminants. Grey water irrigation systems are acceptable for raspberry shrubs, for example, but are most definitely not ideal for low-growing strawberries.

Of course, to prevent potential pathogens from coming into contact with any raspberries, grey water should be introduced into the garden at the sub-surface level of the soil. For good measure, any fruits that touch the topsoil should not be eaten.

Tolerant of mildly alkaline substrates, the red raspberry is a vigorous grower. Its shrubs can measure as much as 8 feet (2.4 meters) tall in optimal conditions, which include full sun exposure and fertile soils. The micronutrients found in grey water should promote the development of new branches, flowers, and fruits. A coarse substrate should help prevent the water from pooling below the shrubs.

9) Bearded iris (Iris x germanica)

Bearded irises are undoubtedly the most eye-catching and vibrant members of the Iris genus. These flowering perennials are must-haves in ornamental gardens. A testament to their popularity and favored status among horticulturists, they are now available in hundreds of cultivars. These spring-to-summer bloomers bear their solitary flowers on towering spikes, some of which may grow as tall as 47 inches (119 cm).

Though bearded iris blooms may look exceedingly delicate, the rest of the plant is known for being remarkably hardy. The tough floral stems and sword-shaped leaves are borne on creeping rhizomes, which thrive in well-draining soils provided with the right amount of moisture.

Though they grow best in neutral soils, bearded irises can become well-established and are likely to survive in alkaline conditions. Moreover, their rhizomes can tolerate salt stress. For these reasons, they are the perfect additions to plots that are irrigated with grey water. Use a drip line or subsurface irrigation system to provide a selection of cultivars with both their moisture and nutrient needs. Just make sure to avoid overwatering them as excess moisture can lead to rhizome rot.

10) Wetland plants (various species)

Many wetland plants thrive in systems that are chiefly irrigated with grey water. These moisture-loving species are equipped with adaptations for stripping the “gently used” water of excess nutrients and potential toxins. In fact, some of them are effective enough to treat and clean grey water, making it safer for use throughout the garden and for other indoor purposes. This form of phytoremediation is one of the most ecologically friendly means of restoring the value of used water.

Constructed wetland systems, which are usually composed of a settling tank (where large particles in grey water may sink) and multiple cells of wetland plants, provide many benefits. Apart from improving the quality of potentially contaminated grey water, both simple and complex designs create new habitats, aid in restoring storm waters, and reduce the load on sewage systems. The best plants for constructed wetlands include the following:

• Rushes (Juncus)
• Sedges (Carex)
• Cattails (Typha)
• Arrowhead (Sagittaria latifolia)
• Blue flag iris (Iris versicolor)
• Common reed (Phragmites australis)
• Pickerelweed (Pontederia cordata)
• Spatterdock (Nuphar lutea)
• Wild rice (Zizania latifolia)
• Sweet flag (Acorus calamus)
• Manna grass (Glyceria maxima)