This is a versatile plant, often used as a filler in hanging baskets, in and around ponds and water gardens, and in aquariums. Water hyssop also is an herb listed in Ayurvedic practice. As is often the case for such vigorous plants, water hyssop has few, if any, serious pest or disease issues.
Light
This plant does well in full sun or partially shaded areas. Positioning water hyssop in a sunnier location will encourage fuller growth. If it’s located in an overly shaded area, the leaves will be more spread out, and the plant will have a sparser appearance. Consult local experts before planting B. monnieri. It may be a better choice for container water gardens or hanging baskets than for bog gardens or ponds that adjoin native landscapes.
Soil
Water hyssop isn’t too fussy when it comes to soil types, except for demanding good moisture. The plant prefers acidic to neutral soil but will tolerate mildly alkaline conditions.
Water
Water hyssop detests drought conditions, and its succulent leaves need a lot of water to thrive. Allowing the soil to dry out is one of the most effective ways to kill the plant. In prolonged dry weather, keeping this plant alive may require daily watering.
Temperature and Humidity
Water hyssop does well in warm and tropical conditions. It can even cope with intense desert heat, provided you make sure that its generous moisture needs are met. If you frequently experience cold snaps or temperatures that are frequently below 60 degrees Fahrenheit, this plant is a poor choice. Humid weather is not a problem, as this plant thrives in such conditions. Dry air will require that you make efforts to keep the soil constantly moist.
Fertilizer
When this herb is planted in the ground or in baskets, half-strength, slow-release fertilizer will be enough to encourage rapid and healthy growth. But feeding is often discouraged since the plant’s natural pattern is for quick, potentially rampant growth, which will only be exaggerated by feeding. If your water hyssop is in an aquatic setting, you shouldn’t use fertilizer unless it’s specifically designed for this type of environment. Feeding can encourage the rapid growth of algae, as well as pollute local water supplies.
Types of Water Hyssop
The Bacopa genus includes more than 70 aquatic plants, many of which go by the common name of water hyssop. Most, however, are native plants that are not cultivated for garden use. B. monnieri is one of the only species commonly sold in garden centers, and there are no named cultivars commonly available.
Pruning
Once plants are established in the landscape, you may need to dig up spreading roots on an annual basis to prevent water hyssop from colonizing where it’s not wanted. This is not a difficult task—just dig up the root and greenery around the edges of the hyssop patch and discard them. Plant parts should not be composted, as root pieces can easily survive to become established wherever the compost is used. In very favorable conditions, keeping water hyssop controlled may be a monthly task. Should stems die back because of dry conditions, clip them off. The plant normally rebounds nicely when its water needs are met once again.
Propagating Water Hyssop
This fast-growing and long-lived plant is easy to propagate from vegetative cuttings or root divisions. Here’s how: You can also propagate these plants by digging up root sections and planting them immediately in the desired location. This method can be practiced in either spring or fall.
How to Grow Water Hyssop From Seed
For the most part, seed propagation is not recommended, since vegetative propagation from cuttings is so easy. The seeds are very small, and successful germination can be hard to achieve. If you do wish to try seed propagation, plant the seeds close to the surface in a sunny location. The soil will need to be kept constantly moist as the seeds germinate and sprout. The seedlings are small and delicate, and you will need to let them grow considerably if you plan to transplant them into individual pots or into new garden locations.
Potting and Repotting
When grown in a pot, water hyssop needs a deep container to accommodate the sprawling roots. Ordinary commercial potting mix is a suitable growing medium. Make sure you select a pot with a sealed bottom, as you want the soil to remain moist. Repotting will become necessary whenever the plant becomes pot-bound, which can be an annual event with this fast-growing plant. Unless they are submerged in a pond, potted water hyssops will require daily watering to keep the potting medium properly moist.
Overwintering
Within its recognized hardiness range, no winter protection is required for this plant, but you should make sure that the plants are not allowed to dry out, which can occur in regions where winters are unusually arid.
How to Get Water Hyssop to Bloom
Water hyssop generally has a long bloom period from spring into fall, provided it gets enough sunlight. Failure to bloom is usually traced to a lack of sunlight. The plant also needs consistent moisture in order to bloom.
Common Problems With Water Hyssop
There are few serious problems with this plant, but you may experience these issues:
Plant Spreads Too Quickly
Planted in a natural bog or shallow pond, water hyssop can spread so thick that it entirely covers the water and prevents light from supporting other aquatic plants. In a small artificial pond, a potted water hyssop can similarly grow so large that it dominates the space. The answer, in either case, is to vigorously prune down the plant to curtail its domination.
Plants Are Leggy and Sparse
A water hyssop that doesn’t get enough sunlight often sends out sparse, long stems in an effort to reach for light. Shady conditions will also reduce flowering. The solution is to prune surrounding trees to allow more light to reach the plant.
Plants Have Died Back
Either drought conditions or unseasonable cold can cause stems of this plant to die back to the root crown. The plant will usually survive both forms of trauma; simply cut off the dead stems and the plant will restore itself with new shoots. Extended cold or drought, however, can potentially kill the plant, roots and all. If you live in an area that hosts white peacock butterflies, this plant is known to attract the caterpillar of this beautiful species.
Further complicating the issue is the fact that various species and cultivars in the Agastache genus are also known as hyssops. The name hyssop is sometimes given to plants with a history of medicinal or ritual use.
