Phalaris aquatica ('Harding Grass') seedlings

How to Grow Phalaris aquatica

Here’s our helpful guide on how to grow Phalaris aquatica – an an attractive perennial grass with similar growth habits and requirements to the closely related Phalaris brachystachys and the popular ornamental Phalaris arundinacea.

Originally native to countries of the Caucasus and Southern Europe, as of the present day the species is considered naturalised to countries including Australia, New Zealand, South Africa and the USA. There are also several popular cultivars of this species (including ‘AQ1’, ‘Australis’, ‘Sirosa’ and ‘Uneta’), as well as some interesting Phalaris arundinacea x Phalaris aquatica hybrids.

In lieu of future tutorials appearing on this website, it’s worth noting that most – if not all – of the advice outlined here also applies to the cultivation of many related species, so (for now at least) this article may be also considered as a basic primer on how to grow the Phalaris in general. Many members of the genus are well-suited to beginners wishing to gain cultivation experience with the wider Poaceae grasses, so why not give it a go and grow something new!

Whether sowing aquatica from seed or by rhizome division, it’s a very simple affair, which will soon establish large bunches of waist-high, grey to blue to green grass that produces densely spiky flowering heads that grow to roughly thirteen centimetres. Aquatica keeps up an amazing amount of growth over the spring and autumn and is therefore considered as an invasive species in some habitats (chaparral, grassland, oak woodland and riparian) – be aware of this when growing it for ornamental or other purposes! Also note that this species will not tolerate any heavy or sustained freezes.

Happily, for anybody who has been waiting for an opportunity to grow this great grass species, the secret of how to grow Phalaris successfully is simply to keep it well-watered. If proper moisture levels are maintained throughout the plant’s lifetime, she will reward you with as much expansion of her gorgeously-hued foliage as you will allow!

How to Grow Phalaris aquatica

Phalaris aquatica ('Harding Grass') seedlings


  • Clingfilm
  • Phalaris aquatica seed
  • Plant mister
  • Plant pot (or other suitable growing container)
  • Potting soil
  • Sieve
  • Water (tap water is fine)
  • Garden fork or spade (optional)
  • Kelp/Worm castings/etc. (optional)
  • Perlite/Pumice (optional)
  • Trowel (optional)

Method – How to grow Phalaris aquatica from seed

  1. Sieve out any larger debris from the potting soil. Optionally, mix in a little kelp or worm castings as fertiliser, as well as some fine or medium-grade perlite or pumice if you want to improve drainage.
  2. Fill the plant pot with the soil and then lightly and evenly tamp the surface down. Make sure to leave it somewhat loose, else you could dissuade the seeds from sprouting!
  3. Using the plant mister, spray the soil’s surface with water until it is moist but not soaked.
  4. Sow the Phalaris aquatica seeds on top of the soil and then gently pat them down one or two millimetres deep.
  5. Improve germination rates and maintain moisture levels inside the pot by covering it with one or two layers of Clingfilm.
  6. Aquatica requires light to germinate, so place it on a sunny windowsill or under suitable artificial lights.
  7. Dependent on their environment, the first seeds should start to germinate after approximately three to five days, although can take as long as a week to a week and a half, in our experience.
  8. Young Phalaris shoots benefit from a bit of support. To this end, once most of the seed you planted has germinated, remove the Clingfilm and sprinkle a little sieved soil between the shoots.
  9. Leaving them uncovered from now on, allow the young plants a minimum of one or two months in which they can grow and (hopefully) develop a healthy, strong, root system. For maximum growth, ensure there is adequate moisture at all times. We prefer to bottom-water every few days, by sitting the plant pot in a larger container which is kept partially filled with water.
  10. Once the plants are big and strong (which demonstrates that they’ve formed a good root structure), they can be transplanted into either a larger container or the ground.

Phalaris aquatica 'Australis' seedlings at a week or so old

Optional – Cloning Phalaris aquatica

  1. Alternatively, you may instead prefer to use your existing clump of mature Phalaris aquatica to initiate a larger patch of grass. If this is the case, first prepare your ground (or suitable large container) by loosening the soil with a fork or till, removing any weeds or larger debris as necessary.
  2. Now you’ll need to divide your clump into plugs – for best results, each plug should be a minimum of five centimetres by five centimetres in size. Alternatively, you can either gently separate each plant by hand (ensuring the roots of each remains intact), or simply cut a diamond shape out of the pot using a trowel (or similar), then transplant the corner wedges as plugs.
  3. At this stage, some growers recommend clipping down the longer foliage so as to reduce the risk of decomposition and encourage new growth. Some also soak the roots/rhizomes of the plants for twelve to twenty-four hours in an organic transplant fertiliser solution (for example, comprising of a few tablespoons each of glacial rock dust and kelp in a few litres of water).
  4. When planting in containers, place one plug into each, filling in the gaps with some potting soil, perlite/pumice, etc. If you’re planting straight into the ground, space the plugs using their width as a guide and leave roughly half of the plug’s thickness between each of them (for example, for five centimetre square plugs, space them two and a half centimetres apart).
  5. Give the plant’s rhizomes the time and space to expand – keeping the soil well-watered and free of weeds or other unwanted interlopers – and your Phalaris patch should thrive. The great thing about this simple Phalaris cloning technique is that one clump of grass can quickly be propagated indefinitely in order to create a wonderfully ornamental stand!