P. praelongus has been grown in the Collection of Aquatic and Wetland Plants in IB, CAS, Třeboň since 1988. The culture was established with stems gathered in the TPA and is used not only for preserving a few tens of vital stems of this species, but and also for growing stems for reintroductions and achenes for germination tests. P. praelongus was cultivated in 2–3 rescue tanks and in one collection tank till 2011. The collection tank was filled with water all the year and the plants overwintered there in close-to-nature conditions, i. e. under water. The rescue tanks had to be emptied at the end of each growing season (mostly in the middle of October), therefore the plants overwintered under a layer of leaves. Comparison of these two kinds of overwintering showed that plants overwintering under water were more vital and were able to blossom in the next May, while a lot of the plants that overwintered under the layer of leaves suffer from dying of roots and stem bases. During the growing seasons 2009–2011, water conditions (pH, concentration of NO3-, NH4-, PO4-) in the tanks with P. praelongus were observed. Monitoring showed that the root and stem dying is probably linked to nitrogen or phosphorus deficit in exhausted substrate, which confirms that this species demands a high content of minerals in calcific substrate and a mellow substrate with a high share of organic substances.
Based on longtime problems with rescue cultures of P. praelongus hibernated dry form were last two rescue tanks abandoned in October 2011. P. praelongus plants has been grown since 2012 in only 3 large flower pots in collection of aquatic and wetland plants. In one tank, they hibernated under water. Flower pots were kept in laminate tank which was dug into ground, and since 1998 has been a part of Collection of Aquatic and Wetland plants. In this tank has been cultures of all P. praelongus in the Czech Republic maintained. Area of tank is about 2,5m2, depth 69 cm, water level is usually between 62–68 cm. Because plants started to weaken at the end of growing season in 2012 due to lack of nutrients, the substrate in flower pots was changed in 2013. Size of this micropopulation is stable many years and is estimated to 50 individual stems of different size and age. Other change of substrate was done in 2015.
Since 2009 has been regulary gathered fruits – achenes and provided to the University of Hradec Králové for germination tests. In 2009 achenes were used for tissue culture established by ing. Kamil Pásek in Ostrava. In 2010, 2011 and 2015 were grown stems from in vitro cultivation in Collection of Aquatic and Wetland plants, which were used for reintroduction in potential localities in 2015 and 2016. Methodology of P. praelongus growing in a rescue culture was standardised in IB, CAS, Třeboň in the frame of the project MGS II-15.