This plant originates from India and has become quite common in the hobby in recent years (2010 +) as it is stocked and farmed by most large aquatic plant nurseries. Hygrophila pinnatifida's fern-like appearance allows it to blend well with mosses and wood. It requires very frequent trimming to prevent it from shading the rest of the surrounding plants. This plant looks redder on the leaf underside. The photograph above is the top view of the same bunch of plants below. Because it doesn't require a substrate, it is often planted higher up on hard scape which then offer us the attractive underside view of leaves.
It is tolerant of wide range of water parameters and is an easy plant to grow with CO2 injection although it can be used reasonably well even in low tech tanks (but success is less certain). If you have tried buying emersed growth forms from dealers and they keep melting, try looking for submerged grown ones instead. Conversion process is where some folks have issue with the plant - the submerged forms are stable and grow easily.
Hygrophila pinnatifida is a popular epiphyte in aquascaping circles as it can grow well without being planted in substrate - it attaches easily to rocks and wood and its reddish coloration and unique leaf shape serves as good contrast against green plants. It can be used in bunches in the mid ground or attached onto any type of hard scape using super glue or thread or cable ties (that can later on be removed as the plant attaches readily to surfaces).
The unique leaf shape and patterning can be seen clearly in this close-up photograph. Hygrophila pinnatifida is a stem plant that will grow continually upwards towards the water surface. If allowed to reach the water surface it will breach the surface eventually and grow emersed leaves and small purple flowers.
It is an aggressive and fast grower that sends out runners continually; it becomes very wild and can grow quite large with a width of 25cm+ when given rich CO2 & nutrients. This plant can be trimmed aggressively to force it to maintain a smaller size and prevent it from shading other surrounding plants. The runners should be cut regularly if you do not want this plant to spread everywhere in the tank.
Propagation is easy as the plant send out runners very frequently. These will spawn plantlets at regular intervals that can be cut and replanted elsewhere.
Key Success factors
Strong lighting gives better coloration
Avoid extreme water parameters
CO2 injection makes it much easier to grow this plant
Not super picky about nutrient levels but potassium levels should not be allowed to bottom out. High tolerance for lean dosing.
How to get it redder
Stronger light (higher PAR values)
Low nitrates (5ppm & below)
This is one of the plants that exhibit much redder colors under nitration limitation - meaning that the plant grows much redder if it is starved for nitrates. Over-do this and the plant will stunt. However, since it is tolerant of much lower nutrient levels than other plants - other plants will usually stunt first.
how to trim
One of the easiest plants to trim. Cut off the stem above one of the internodes and the plant will spawn smaller plants from the remaining internodes. The runners should be cut regularly if you do not want the plant growing everywhere in the tank. Plantlets can be replanted easily even at small size.
This is one of the more common issues with this plant. Some online forums cite these plants as "potassium hogs" and typically diagnose these issues as potassium deficiency.
we find that that while potassium is important (not only for Hygrophilas, but the general health of most aquatic plants), there is never a need to have an extra high dosage of potassium just to maintain the health of this plant. It is not particularly demanding in terms of nutrients, contrary to what most folks think.
If your plant is very pale colored (such as the one shown in the picture below) and have yellow edges along the pinholes, and you have not been dosing potassium regularly - it may well be a potassium deficiency. However, if you are already dosing 20-25ppm of potassium in your tank and still have pinholes in your leaves; you should rule out potassium deficiency and move on to test other factors. Many factors contribute to the health of aquatic plants - availability of CO2, as well as all other nutrients and having holes in older leaves can be tied to a number of issues, not just potassium. Do not get sucked into having nutrient tunnel vision.
Are you dosing excessive amounts of Iron/Trace just to get the plant to color up ? If so, you might actually be doing it more harm than good - and having more iron won't turn it any redder either. If you have twisted/curled leaves this might very well be the case. For all of the examples above, the plants were grown with no more than 0.05ppm Fe/trace per day. ( that's 0.35ppm a week).