Plant review: Cosmos 'Xanthos - the first compact yellow, early-blooming variety

One of the members' trials for Which? Gardening this year involves yellow cosmos. Later in the year they'll be reporting on participants' experiences with the variety 'Lemonade', but yellow cosmos has already caused a stir, with the promotion of Cosmos 'Xanthos' last year.

Short and compact, its main "ooh" factor was that it comes into flower early, offering blooms potentially from May to October, making it the first yellow-flowering cosmos that suited UK weather. Previous varieties just got going about the time of the first frosts.

It was a Fleuroselect's Gold Medal winner for 2016 on the grounds that it was uniform, well branched and very suitable as a pot plant, and added a new colour to the dwarf Cosmos range. For the horticultural market, it is ideal for transport (being compact), has a short production time which makes it an early-season attraction in the garden centre. They described it as "Xanthos, a revolution for the compact Cosmos market".

At a height and spread of 60 x 40 cms (24 x 16 ins), they're a good choice for underplanting. I tried them out in the front garden. Plenty of other people pounced on them too. In the UNHCR Border Control Garden at Hampton Court Flower Show, they were part of an airy, semi-wild planting by Tom Massey and John Ward which helped win them Best Conceptual Garden.

Planting, including Cosmos Xanthos, in the UNHCR Border Control Garden, RHS Hampton Court 2016.

A month later I spotted them in the beds of the Victoria Embankment Gardens, London.

Planting in the Victoria Embankment Gardens, Westminster, August 2016

They tick several boxes:

• Soft, pretty yellow
• Compact
• Short
• Bushing out into space-filling sturdy plants
• Good in mixed planting
• A long flowering period

Graham Rice, in his article on the RHS website, says:

This is the first Cosmos bipinnatus type with yellow flowers that is actually worth growing.

However, a number of bloggers tried them last year and there's something of a consensus. The Chatty Gardener said:

If there was a problem with them, it’s deadheading, as the flowers are packed onto the stems, making it difficult to snip off spent blooms without accidentally removing flower buds.

Michelle Chapman at Vegplotting said:

I've found this variety disappointing to look after as the flowers go over very quickly. Sadly many of the spent flowers are not separate enough from the buds, so I end up removing both when I dead head the display.

Michelle also comments on fading colour, though this may be due to their hot south-facing position.

And what did I think? Well, pretty much the same. Mine arrived as plug plants from Thompson and Morgan at the beginning of April. They grew well. When they bloomed, the soft yellow did fade with age, but I didn't mind that so much.  What I didn't like were the brown dead blooms. The first flush was lovely but, once the flowers began to die off, the plants began to look messy. You either have to put up with the brown or pick it off.

I should have called this blog "The Lazy Gardener" because -  you know? - I can't be bothered. Especially when it means being bent double over short plants. When I tried, I found that I was indeed pulling off buds along with the spent blooms, and I wasn't about to snip them off individually.

To give Xanthos its due, this didn't stop it in its tracks. I got flowers coming through right up to late summer, just not, I suspect, nearly as many as I would have done, had I assiduously done the deadheading.

Cosmos Xanthos growing in the south-facing front garden. Both here and in the picture at the top you can see how much brown you end up with.

Would I grow them again? Well, I won't be rushing to get more, but they definitely have a place. If you want to grow them - and there's no denying that they are a very pretty colour and bush out beautifully to fill up space - I'd suggest raising them up and putting them somewhere you pass regularly so you can deadhead little and often on the way to somewhere else.

Meanwhile, Thompson and Morgan describe 'Lemonade' as an improvement on 'Xanthos'. It's a multi-flowering subtle yellow cosmos with a central white eye, bred by T&M from a very bright yellow, late-flowering Japanese cosmos and an earlier-flowering shorter variety. The result is - again - a "major breakthrough in cosmos breeding" and, they say, blooms prolifically throughout the summer on short to medium-high, branching plants, making it perfect for patio pots, as a floriferous border filler, and a cut flower.

I wonder what the readers of Which? Gardening will make of it?