Stipa gigantea is a very popular grass. In fact, I think it is probably most gardeners’ favourite grass. And with very good reason. It is tall and quite delicate so not overbearing. It doesn’t get enormous and need dividing every year or so but, even when it does need reducing in size, it’s not a huge task as it is with some of the really big species. It is evergreen, remaining as a low mound of basal foliage throughout the winter, and has a long season of interest.

But the feature most often mentioned is its transparency, a quality that can be used to good effect when it’s planted where it can be seen through, allowing glimpses of the garden beyond.

Stipa gigantea  – where does it belong in the plant world and what does the name mean?

It belongs to the grass family, Poaceae, one of the largest and most successful of the flowering plant families, with nearly 800 genera and about 12,000 species. It also has the widest distribution with grasses growing on every continent and in every ecological niche. Grasses are also of huge economic importance. They provide us with much of our food, – rice, wheat, rye, barley, oats, maize, and sorghum are all members of the grass family – are the main food source for wild and domestic animals, and also have a part to play in many cultures, in areas such as house building, sport, music, and landscaping.

But let’s concentrate on this one example of a grass before it gets stiffled by its enormous family.

The name Stipa is from the Greek, stuppe meaning tow, the coarse and broken part of flax or hemp prepared for spinning, alluding to the flaxen appearance of the feathery awns of the original species. It is often referred to as feather, needle, or spear grass.

The specific epithet, gigantea, speaks for itself although I haven’t been able to find details of why it was applied to this grass. It certainly isn’t a giant grass but, maybe, it’s the largest in the genus, Stipa. Or does it refer to the spikelet or floret, which, as we shall see, is quite large?

Now we can find out why it’s so highly thought of.

A grass for the summer

During May the stems, known as culms in grasses, start forcing their way up from the mound of evergreen basal foliage. As it reaches its eventual height, the culm produces an inflorescence, an extremely loose, open, pendulous panicle with a main axis, called a rachis and many branches. Each branch bears a large purplish spikelet, 25mm long with a long awn of about 10cm.

In a little over two weeks the inflorescence stiffens and becomes more upright. The spikelets open exposing the stamens. The pollen is shed and then the stigmas become receptive. Grasses are wind pollinated. However, this year the wind intervened just a litle too enthusiastically.

In the first two images above, you can see the plant in full flower with the yellow, hanging stamens and white, feathery stigmas much in evidence. As the plant matures the spikelets lose some of their purple sheen and become a little browner.

The third image was taken just six days later and there are just a few stigmas remaining. During this time we experienced day after day of strong winds, which battered this plant ceaselessly. Whether the wind damaged the stamens or blew the pollen away too quickly I don’t know but the plant hasn’t produced any seed. There might well be another explanation so, if you have any ideas, do add a comment at the end of the post. Normally, the ovule is fertilized with pollen and develops into a seed, in a grass called a caryopsis or, more popularly, a grain.

The three images below were taken another ten days later and are beginning to show the golden colour for which this grass is well known. You can see the spikelet now consists of two bracts with a structure in the centre, covered in hairs and retaining the long awn. This is where the seed develops and when ripe it falls to the ground. The two bracts remain and give the plant a golden veil-like appearance, which lasts into autumn and beyond until wind and rain batter down the brittle stems.

Now let’s take a dive into the detail

Stems and leaves

You can just about make out the edges of the sheath in the image. The blade is the flattened part, which begins at the top of the sheath and grows away from the culm. You can see the lower part of one in the images. The ligule is a membranous growth at the junction of the sheath and blade. There is great variation in this structure and it can be important in botanical identification of different genera and species of grasses. Its use seems uncertain but could be to keep rain from entering the sheath.

Panicles, spikelets, florets, and flowers

The first image is of an inflorescence just emerging from the top of a culm. It is a panicle with a main axis, a rachis, and many branches, the last one a pedicel with a spikelet attached. In the second image the panicle has become less lax and more upright and the spikelets have opened to reveal the flowers. The spikelet is the basic unit of a grass inflorescence so I took a closer look.

The spikelet consists of two basal bracts called glumes and one or many florets – in Stipa gigantea there is one. A floret consists of two bracts, the outer one called a lemma, and the inner a palea, and the flower. In the third image you can see a pedicel with two glumes and, below them a lemma with the long awn, and a palea.

The flower, enclosed and protected by these bracts, comprises an ovary with two styles, ending in feathery stigmas, and three stamens with threadlike filaments and pollen-producing anthers. All these features can be clearly seen in the images below.

In the first image the glumes and the lemma and palea have opened slightly allowing the stamens to shed their pollen. You can see the hairs of the lemma showing between the glumes, and the long awn. These awns are more in evidence in the second image, and here the bracts have opened further and you can see the feathery stigmas, which mature after the stamens. The third image is a close-up of the spikelet and you can see the stigmas, lemma, and filaments and anthers. Notice, too, how brightly coloured and shiny the glumes are at this early stage.

Seeds to provide the next generation

Unfortunately, as mentioned above, my stipa hasn’t set seed this year but it looks the same as when seed is produced. In the first two images you can see the pedicel with the two glumes, now dried and golden, and, between them, the hairy lemma with its long awn. This is where the seed, called caryopsis in grasses, would develop. I haven’t been able to find out or see what has happened to the palea.

When the seed is fully ripe this structure falls, the weight of the seed causing the sharp point to pierce the ground. The awn then twists into a spiral, as you can see in the third image, screwing the seed into the earth. Its task completed, the awn then breaks off and the seed awaits favourable conditions to germinate and grow into a new plant. The first image below shows a young plant, germinated from last year’s seed and now growing away.

The second image shows a panicle, the seeds having dropped and the spikelets retaining only the glumes. The third image shows a clump ready to decorate the garden with its golden airiness into the autumn.

Now we’ve seen the detail let’s get back to the garden and see how to grow it

Stipa gigantea forms clumps of tough, evergreen foliage and blooms in the summer, the large panicles held high above the foliage on stems about 1.8m tall. It is native to Spain, Portugal, and Morocco growing in dry, sandy soils, which gives us an indication of its preferred growing conditions. It needs a sunny, well-drained position but, given such a spot, should be hardy throughout the UK or to Zone 6 in the US.

Grasses can be grouped into two categories, cool-season or warm-season growers, depending on when their periods of active growth occur. This is governed by temperature, light intensity, and available moisture. Understanding a plant’s responses to these factors can help us in selecting which grasses to grow and choosing the best times for planting, dividing, and propagating them.

Stipa gigantea is a cool-season grower and begins growth in late winter, developing good foliage by early spring, and flowering in early summer. This coincides with a mixture of  warmth, moisture, and sunlight well suited to this plant. As the summer advances, temperature and light intensity increase and rainfall decreases, conditions that are stressful to a cool-season grower so it will go partly or fully dormant. It will resume growth with more favourable conditions at the end of summer and continue until extreme cold forces it to stop.

It should, therefore, be divided or transplanted from late winter into early spring, and again from late summer to mid-autumn. It should not be moved or divided as it goes into or is in a dormant state. Whether or not this applies in a year such as the one we are experiencing here in the UK with so many dark, cold, wet days I do not know.

In conclusion

For some time I have wanted to look in detail at grasses and realized that the best one to choose would be Stipa gigantea because of its size. As soon as I started my research I also found that it seemed to follow a fairly standard pattern for a grass so was an ideal candidate with which to make a start.

But, my goodness, going from no knowledge to understanding enough to make sense of the subject was a very steep learning curve. Glumes, lodicules, and spikelets were completely unknown to me but now I think I could identify at least some of these features on other grasses. I found two books especially useful: The Colour Encyclopedia of Ornamental Grasses by Rick Darke and Ornamental Grasses by Roger Grounds. Rick Darke’s book could be regarded as a grass bible, absolutely filled with information, explanations, and beautiful photographs. Roger Ground’s book is similarly wide-ranging but with a slightly different take on the subject. I found the combination helpful in gaining an understanding of the subject. And, of course, the internet provides information from its vast store – some more useful than others.

However, the most important aid to understanding is actually having the plant in front of you and comparing what you see in real time with what you can see on the page. Taking photgraphs helps even more and is a permanent record of what you saw and, of course, is an excellent way of sharing the experience.

Once again I found that even this small amount of additional knowledge has given me a new perspective. I hope I will be able to look at grasses with fresh eyes and appreciate their beauty more than ever. Here are just three that it will be interesting to take a look at. But that will have to wait until another day.

Post script – I’ve saved this until last!

Stipa gigantea has had a name change – it is now Celtica gigantea. The Royal Botanic Gardens Plants of the World Online has accepted this new name but I imagine it will be some time before it filters down to gardeners. You can find full details in a paper published in The Botanical Journal of the Linnaean Society. It makes fascinating reading!

Find more information

Internet

• Plants of the World Online

Books

• The Colour Encyclopedia of Ornamental Grasses by Rick Darke
• Ornamental Grasses by Roger Grounds

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Plants in detail See why I think looking at the detail is so important

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