Persicaria

by Kate van Heel

Persicaria is a genus of around 100 species of colourful perennials, found in pretty much every country worldwide. Along with other members of the Polygonaceae family, they are commonly known as knotweed. Although they have a reputation of running without restraint, there are some fabulous garden plants that I think should be given a chance.

Persicaria amplexicaulis and its many cultivars will tolerate a wide range of soils in sun or light shade, often preferring moist soil, but will grow in drier conditions too. The slim, tall, dark spikes of red, white or various hues of pink flowers bloom all summer long until the frost puts a stop to them.

One of my favourites is Persicaria amplexicaulis ‘Pink Elephant’, not least because I like the name! It grows to about 70cm, producing pink flower spikes from July until October, bulking up gently but by no means running out of control.

It grows here with Astrantia ‘Gill Richardson variety’ and some dark leaved Heucheras, together producing a long lasting display.

Persicaria amplexicaulis ‘September Spires’ is a robust, taller plant than ‘Pink Elephant’ with a more lax habit, producing pale pink flowers and with mid green foliage. The foliage can look slightly messy but growing it amongst other plants means the flowers waft around gently giving a pleasing effect.  As its name would suggest, it flowers later than ‘Pink Elephant’, coming into flower probably around the beginning of August and lasting into October.

Persicaria amplexicaulis ‘Alba’ grows in quite deep shade under a Sorbus and fights for space with the self seeding Melica grass, alongside Eurybia divaricata (formerly Aster divericatus). However, it manages to hold its own and lightens a shady area with its soft, airy flower spires. Another reason to grow this Persicaria is because it knows its place and doesn’t try for world (garden) domination! In my garden it tends to start flowering at the beginning of August, but that may be because of its position; more sun would probably help it into flower earlier.

There are also many Persicaria grown just for their foliage. Persicaria microcephala ‘Red Dragon’ is distinguished by having red stems and leaves which emerge purple-brown, turning silver-purple, and finally green with maturity. It is clump forming but can be very sprawling in habit so give it plenty of room.

Another persicaria that has fabulous foliage is Persicaria runcinata ‘Purple Fantasy’. Unfortunately it is a very vigorous plant, spreading by means of runners. When it decided to take over the area it was planted in, it  had to be relegated to the shaded front garden to take its chances below an old laurel.

There are several other Persicaria species in the garden ( I didn’t realise there were so many!), all earning their place for one reason or another. Persicaria campanulata spreads around but keeps producing flowers for an incredibly longtime;  Persicaria amplexicaulis ‘Dikke Floskes’ has masses of thick bushy deep red flower spikes, growing alongside Helenium ‘Sahins’s Early Flowerer’ in the red and yellow border; Persicaria bistorta ‘Superba flowers earlier in the year, giving a welcome burst of pale pink flower spikes; Persicaria affinis ‘Superba’ has been growing in my garden for more than twenty years and is perfect for using as ground cover at the front of a border under the shade of an old apple tree. 

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The good thing about Persicaria is they are easy to propagate – just divide mature herbaceous clumps in early autumn or late winter and pass on these wonderful plants to all your friends!

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Kate van Heel

Pictures courtesy of Kate van Heel