episode 67 | show notes & advice
Today Sarah and Arthur are talking about cosmos and zinnias – two stalwarts of the cutting garden and the container garden. Cosmos and zinnias are brilliant in the garden, flowering profusely all summer long. And they are excellent cut-and-come again flowers that thrive on being cut to fill vase after vase, so they are Sarah and Arthur’s favourite plants to be sowing and growing now.
In this episode discover
- Why cosmos are so special for Sarah and her top tips for extra flowery plants
- The Aztec series Zinnias ‘Sunny Mix’ and ‘Burgundy Bicolour’ Arthur is growing as lovely spillers for his containers
- The best method of sowing zinnias in the garden or pots
- Plant strawflowers now for a colourful pot until Christmas
- Why Sarah sows the hardy annual Cerinthe major now for flowers this autumn
Episode 67 advice sheet
Cosmos are dear to Sarah’s heart because they were her starting point. Her first metre square trials were with cosmos, calendulas, antirrhinums and Salvia viridis ‘Blue’. Cosmos came top for productivity – in terms of the number of stems per week and the number of weeks in flower – from July going on until early November.
Over the years there has been a shift – a lot of the Cosmos seed available now is being grown in Morocco where the microclimate is different, with a longer growing season but a shorter day to us. We are finding plants will grow, grow, grow but flower late. We’ve found ways to avoid this:
Sarah’s top cosmos tips for flowery plants
1) Cosmos thrive in poor soil so adding grit to decrease fertility is a good thing to do. This should ensure more flowers, appearing earlier, that are less prone to rust. Sarah is doing a trial on this right now at Perch Hill.
2) Sarah increasingly loves the more compact varieties of cosmos – the middle sized ‘Fizzy White’ in place of ‘Purity’, and ‘Rubenza’ instead of ‘Dazzler’– a brilliant rich carmine and a bit more compact.
Arthur’s favourite cosmos for containers
Arthur finds the Sonata series too compact – each stem gives a flower and tires out - a bit like hens that lay every day then go into moult. Like Sarah, he prefers the more delicate, airy ‘Fizzy White’ and ‘Rubenza’. He doesn’t recommend ‘Purity’ or ‘Dazzler’ for pots as they can push 6ft when fully grown.
Read our complete cosmos growing guide for how to plant, grow and care for cosmos.
Zinnias for pots
Arthur is trialling the Aztec series Zinnias ‘Sunny Mix’ and ‘Burgundy Bicolour’ for profuse flowers to spill out of pots. He finds bigger zinnias are too high maintenance for containers.
Plus zinnias give amazing cut flowers, lasting four weeks in a case if kept in a cool spot.
Sarah’s top tips for zinnias
Sarah says now is the time to plant, or even sow zinnias, as they catch up so quickly. A few important things to know:
· Like basil, zinnias hate cold nights. Sarah’s rule is if you are happy to have supper in your garden without a blanket, then zinnias will be happy planted out too.
· Again like basil, best to water zinnias in the morning. They like lots of light and are happy with humidity and don’t like the cold.
Sarah’s favourite zinnias
Sarah likes chartreuse Zinnia ‘Benary’s Giant Lime’ and also ‘Queeny Lime Red’ which opens in bud really green, the centre is dark jewelly red, then becomes more muted, with the petals turning from green to pink.
There is a new Zinnia ‘Queeny Lime Orange’ which Arthur loves and reminds him of a cupcake packed full of e numbers.
How to sow zinnias
Zinnias don’t like root disturbance so you can direct sow straight into the garden, a pot or a deep window box. Just scatter seeds straight in and thin to a good spacing – 25-30 cm between each. Zinnias need good air circulation to prevent disease. Recent Zinnia breeding has really improved resistance to fungal botrytis which is great news.
To sow under cover, Arthur recommends our new rubber seed trays as it is easy to massage the plugs out, minimising root disturbance.
Read our complete zinnia growing guide for more information on how to plant, grow and care for zinnias.
Plant strawflowers for everlasting colour
Sarah recommends planting strawflowers (previously known as helichrysum and now called xerochrysum). Sown as seeds or as a plug in late May, into a pot for colour until Christmas, first as fresh flowers then as dried flowers as their colour doesn’t fade. They make ideal low maintenance, living and everlasting container plants. Sarah is currently trialling more strawflowers at Perch Hill.
Cerinthe for autumn flowers
Sarah does three sowing of Cerinthe major. One in autumn, one in early spring and one now. As a hardy annual, sown now and planted in June or July it will come up to peak production just as night time temps drop in August/September but as it’s hardy it doesn’t bat an eyelid.
If in doubt, pinch out!
Sarah’s main rule for cosmos and zinnias is once you have three pairs of leaves, pinch out the tips so the growth hormone pushes out for short, bushy, more productive, flowery plants.