Samolus valerandi is a water-loving herbaceous plant and is more commonly known as brookweed or water pimpernel. For most of plant taxonomic history, it has been classified under the Primulaceae family, which includes approximately 800 species, some of which are referred to as primroses. Many of these are garden and pond favorites due to their pastel-colored blooms and well-balanced leaf structures. Although still frequently reported to be a member of Primulaceae, it was recently re-classified under Samolaceae, which includes a singular genus – Samolus.
Considered a ‘cosmopolitan’ species, a blanket term for globally widespread plants and animals, S. valerandi is found on all continents with the unsurprising exception of Antarctica. This distribution is fairly unique in the Samolus genus, as the brookweed’s closest relatives are restricted to smaller regions. Perhaps this common herb has gained global footing because of its ability to grow as the plant counterpart of an amphibian, both underwater and above ground.
Found mostly in coastal areas, brookweeds have smooth ovate leaves and are typically unbranched. This small plant tends to go unnoticed in natural settings, as its foliage can be hard to distinguish from that of other herbaceous plants and its plain white flowers extend to just around 1/8th of an inch across.
Though brookweeds are often overlooked in the wild, they are highly popular additions to curated ponds, gardens, and paludariums. With an affinity for growing in wet conditions, particularly in bright seaside, riverbank, or swampy environments, this ornamental herb likes being situated in watershed or wetland areas with an elevation of up to 3,000 meters. So long as minimal shade and water are abundant, it can tolerate an assortment of biomes in both temperate and tropical zones.
Brookweed Growth, Hardiness & Climate
Brookweed will thrive best in temperate or tropical climates and under bright full-day sun exposure. This plant prefers to grow in moist or wet soils, and can even grow in shallow water or fully submerged, though an extended period of full submersion is not recommended as this can compromise its longevity. This adaptation to wet conditions means the plant has a high chance of survival even in the midst of a rainy spell.
It prefers neutral to basic (alkaline) soil and can tolerate a moderate level of soil salinity as well. Take note that the plant spreads by reseeding itself, as its flowers develop into capsules which release tiny seeds upon maturation. Its tendency to grow slowly, however, will prevent it from spreading too rapidly around the pond or garden. Though brookweeds can tolerate a considerable amount of frost, they have difficulty surviving through extended cold periods with temperatures lower than 12 ˚C. Conversely, leaves may get scorched and roots may dry out in markedly hot conditions.
How to Plant Brookweed
Brookweed is suitable for sandy, loamy, or clay soil. Prior to preparing the soil, you may want to check for alkalinity to ensure that the pH is neutral or mildly basic. To plant brookweed, sow seeds onto the surface of loosened moist soil, preferably in pots. Place the pot in approximately 3 cm (or about an inch) of standing water to keep the soil moist. Regularly monitor the soil surface for any pests and ensure that it remains moist throughout. Once the seedlings have grown into a manageable size, you may increase the water depth in increments, until it is about as deep as the height of the pot.
Once the seedling is large enough to withstand outdoor/exposed elements, you may outplant it into your garden or around your pond. Once brookweed plants are mature, they can be divided at the base and propagated during the summer months. If intended for fully indoor growth, make sure to keep the setup well-lit.
How to Care For Brookweed
Although temperate or tropical pond conditions are suitable for the proper growth of brookweed, it would be wise to regularly monitor your pond’s water and soil parameters, especially after extended periods of rainfall. Brookweed can tolerate saline soil and brackish water, but its growth may be compromised by an acidic pH level. In cases where your pond water pH drops to acidic levels, you may want to adopt a more active form of alkalinity control by adding small amounts of lime or baking soda. Additionally, ensure that the pond’s daytime temperature is maintained within the range of 16 – 24 ˚C (60 – 75 ˚F). The plant may tolerate temperatures beyond this range so long as fluctuations are gradual and do not dip to below 12 ˚C (54 ˚F) or increase to above 32 ˚C (90 ˚F).
As brookweed is averse to growing in shade, ensure that the plant is situated in an area that receives ample sunlight, and transfer any plants around it that may block out the sun. Regularly check the foliage for pests, mildew, and leaf spots, and trim any leaves that have been affected by disease. Keep in mind that a healthy brookweed will flower in the summer months and subsequently produce seed-filled pods, as it has a wondrous capacity for self-fertility.
How to Winter Brookweed
Generally, S. valerandi persists over winter and can tolerate a small amount of frost. As daytime water temperatures drop to below 15 ˚C, allow your brookweed to become dormant by withholding the addition of any pond fertilizers. Remove any dead leaves or plants on the surface of the pond. Prune your brookweed and transfer your pot to the bottom of the pond, where water temperatures tend to be warmer than the pond surface in winter. This unique characteristic of ponds also explains why fish tend to stay close to the bottom during winter. If you have a greenhouse, you may also opt to remove the plant from the pond itself and take it indoors. You may leave the pot partly submerged and in a warm area of the greenhouse.
Is Brookweed Invasive or Toxic?
Though brookweed has a widespread distribution and creates its own seed bank via self-pollination, it is not considered invasive as it does not compete with endemic plants in non-native regions. Dispersal of brookweed seeds in water is limited as the dry seeds tend to rapidly sink to the pond bottom. Long-distance dispersal of their seeds is also primarily facilitated by animal movement, though their seeds do not survive when consumed by birds. Brookweed foliage is not considered toxic and may be economically important because of its medicinal properties.
Where to Buy Brookweed & Seeds? (UK & US)
Brookweed can be purchased from aquascaping shops and occasionally from online stores that supply pond and aquarium plants. They are readily available as 6 x 5 cm plants in plastic pots that can easily be incorporated into well-established pond setups. As a rule of thumb, do be aware that plants you can purchase online may not be native to your area and may have special requirements for growth.
