If unpaved drainage ditches and collection ponds were more common locally, sweet flag, Acorus gramineus, might be also. It can provide a nicely neat border for such waterways, where the ground is too steep and damp for mowing. It can migrate into muddy situations and even into shallow water. Its dense network of fibrosus rhizomes helps to retain mud.
‘Variegatus’, with elegantly elongated and variegated leaves, is the most popular cultivar locally. It is rare in nurseries, but occasionally shared by friends and neighbors who grow it. Propagation by division is very easy. Single shoots or clumps of shoots grow if merely plugged into damp soil or mud. ‘Pusillus’ lacks variegation, and develops stouter leaves.
Sweet flag aggressively excludes other herbaceous vegetation, but does not migrate too rapidly. Plucking shoots and plugging them elsewhere accelerates migration. The dense foliage might get a foot deep. Individual leaves are very narrow, like grass. The mundane bloom is easy to ignore and is uncommon where the soil is not often saturated or muddy.
Ducks somehow find water. They eventually visit most home garden ponds that they can fit into. Duckweed, Lemna minor, is likely to come with them. It adheres to waterfowl and other wildlife for that purpose. It proliferates very efficiently, and almost typically becomes a nuisance. Eventually, proliferation in a healthy pond should stabilize to a tolerable rate.
Individual duckweed plants are tiny. Their oval leaves are typically less than a quarter of an inch long. Each floating leaf extends its single root less than three quarters of an inch into the water below. Plants produce no more than four rooted leaves before dividing into a few smaller plants to repeat the process. Bloom and subsequent seed are uncommon.
As a floating aquatic plant, prolific duckweed might obscure koi and submergent aquatic plants within garden ponds. However, it also helps stabilize healthy aquatic ecosystems. In fact, it is useful for bioremediation of agricultural and industrial applications. It absorbs detrimental substances from water, while producing fodder and biomass for composting.
Home gardens and landscapes should be compatible with their respective climates. For local chaparral climates, plants that do not need much watering through the long and dry summers are appropriate. Aquatic plants are the extreme opposite. They require regular replenishment of the ponds that they inhabit. Arid warmth increases their need for water.
Aquatic plant can not be ‘drought tolerant’. Several, such as duckweed, water lettuce and water hyacinth, float over the surface of water. Water lily and lotus inhabit the mud below the water, and extend their foliage to float over the surface of the water. Waterweeds stay completely submerged, with or without roots. Aquatic plants need water for their survival.
Marginally aquatic plants are somewhat less dependent on water. Cattail and yellow flag iris inhabit shallow ponds and saturated soil, but can survive if their situations drain for a while. If they stay too dry for too long, they can initiate dormancy, and then recover when saturation resumes. Canna inhabits either shores of shallow ponds, or evenly moist soil.
Regardless, all aquatic plants require maintenance that is completely different from what terrestrial plants require. Even those that need only minimal maintenance will eventually necessitate muddy and messy interaction. Much of such interaction is under water that is difficult to see through while murky. Aquatic plants are innately heavy and totally sloppy.
Moreover, some common aquatic plants grow like weeds. Water hyacinth and giant reed are two of the most invasive exotic species in California. So, not only are they sloppy, but they are also voluminous! Because they are very invasive, they should not inhabit ponds that they could escape. Besides, giant reed is too overwhelming for most home gardens.
Few home gardens include natural ponds or water sources to contain as ponds. Garden ponds are therefore mostly contained within some sort of sealed infrastructure, and need replenishment to compensate for evaporation. Fountains aerate the water for a healthier ecosystem, but also increase evaporation. Some tall aquatic plants also consume water, as the foliage that extends above water transpires.
Although not directly toxic, canna has a unique reputation of lethality. Its spherical seeds are so hard that they were historically used as shot. Many victims are now pushing up daisies. Those who survived were pulling out cannas.
Old fashioned varieties that get up to six feet tall seem to be at least as popular as shorter modern varieties that get less than half as tall, probably because their bold foliage is as appealing as their colorful but awkwardly structured flowers. The big leaves can be cool green, rich reddish bronze or variegated. Red, orange, yellow, pink or rarely white flowers that bloom from summer to autumn are striking amongst the lush foliage, but are too perishable to be good cut flowers.
Stems that have finished blooming should be cut to the ground to promote more colorful new foliage and bloom. Mature colonies (of rhizomes) can be divided while dormant through winter if they get crowded enough to inhibit bloom every few years.
Taro was grown as a vegetable in ancient Egypt. It was grown in India before that. A few hundred varieties were cultivated in precolonial Hawaii. Taro was likely native to southeast Asia, but has been in cultivation for so long that it is difficult to know where it originated from. In modern American gardens, it is known as elephant ears, Calocasia esculenta, and grown for its striking foliage.
The big and broad leaves are held as high as six feet on long petioles (leaf stalks), and flare out as broadly as three feet, although many varieties get half as tall and broad. Some varieties have weirdly dark foliage. Others have green leaves with colorful veins. A few are simply jade green. Any of the deciduous foliage that lingers into winter should be cut back before spring.
Since they are naturally bog plants, elephant ears likes very rich potting soil and plenty of water. Muddy clay soil that will not float away works fine for pots submerged in ponds. (Ick!) Partial shade is important. Leaves can get roasted if too exposed. To propagate, corms can be divided while dormant in winter. All parts of elephant ears are toxic until cooked.
The fragrant flowers of water lily are unreal! They either float on the surface of the water, or hover just above. Abundant pointed petals radiate outward from central tufts of pronounced stamens. Most flowers are soft hues of yellow, pink, blue, lavender, peachy orange or white. Some are brighter yellow or pink, or richer shades of red or purple. Some open in the morning. Others open in the evening.
The rubbery leaves that float on the surface of the water are nearly circular. Some are symmetrically cleft to the center, like Pac-Man or a pizza with a slice taken out. The thick rhizomes that the foliage and flowers emerge from stay buried in pots or mud under the ponds that they live in. Rhizomes can be divided to propagate, but take a year or so to recover and bloom.
During a drought, there really is no way to use less water in a garden pond. Aquatic plants can not survive without adequate water; not to mention fish! Pumps that circulate water must stay submerged to operate properly, and to not get damaged by operating without water. Some degree of water needs to be added regularly to compensate for evaporation.
Water does not evaporate from below the surface of the water. Therefore, depth is irrelevant to water loss. The area of the surface of the water is more important. Sunlight and wind accelerate evaporation. So do fountains or pumps that broadcast water through the air for circulation. Aquatic plants that stand above the surface of the water lose water to evaporation from foliar surfaces.
Yet, most of us who enjoy gardening cannot resist growing aquatic plants if a pond is available. Not only do they provide distinctive foliage and bloom, they also provide shelter for goldfish or minnows that control mosquitoes. They keep water clearer by competing with algae.
Submerged aquatic plants, like anacharis, do everything in the water. Some do not even need soil to root into. Because they do not come above the surface of the water, they do not affect evaporation. None of the floating plants, like water hyacinth, water lettuce and duck weed, have any use for soil either, although some of the leafiest sorts can accelerate evaporation.
Water lilies and lotus are emergent aquatic plants, which naturally live in mud on the bottom of ponds, but develop foliage and flowers that emerge and float on the surface. Although they have the potential to affect evaporation, most are more likely to inhibit evaporation by keeping water shaded. In garden ponds, they must be potted, and should be under at least a foot of water.
Relative to other aquatic plants, bog plants such as cattails, aquatic cannnas, and blue or yellow flag iris consume the most water from saturated soil at or just below the surface of a pond. They produce the most foliage that stands well above the water. Like water lilies and lotus, bog plants need to be potted, but with the tops of their soil barely below the surface of the water.
Pots should be low and wide, and obviously do not need drainage holes. Unnecessary holes only spill a bit of soil, and allow roots to escape and grab onto the bottom of a pond. Good old fashioned soil (yes, dirt from the garden) is fine. Good quality potting soil merely floats away.