This month is a good moment to use the glasshouse to start off some annual flowers for cutting later in the summer. I am sowing some half hardy annuals at the moment: sunflowers, snapdragons, cleome and of course cosmos. All of these could potentially be sown direct out of doors once the weather warms, but by sowing them now they are given a head start that will mean more and bigger flowers, earlier in the year. They are much more likely to survive and thrive with this treatment, which gives you sturdy little plants to plant out into the still-warming earth in May, rather than tiny little struggling seedlings, emerging at the same time as the slugs. Timing wise, if you are going to sow them in the greenhouse the trick is to do so six weeks before the last expected frost date. Earlier and they may grow leggy and weak in the protected environment of the greenhouse, and will get a bit of a shock when they finally go out into the colder and wilder environment of the garden. Obviously, this date will be different depending on where you are, but a fair chunk of the country should be frost free by the beginning of May, which means sowing around mid-March. Adjust to suit your own gardening conditions.
Cosmos is a lovely thing to grow for cutting, or just for wafting around in borders. Cosmos bipinnatus ‘Purity’ is a particularly easy cultivar to germinate, and so is a good place to start if you haven’t grown them before, but none of them are exactly tricky. They have lovely, big, slightly floppy white daisy flowers with a golden centre. They work well in a pastel scheme or bunch, but are also gorgeous as a splash of lightness among brights. ‘Gazebo Red’ has a lovely deep pink flower produced on plants that stay bushy and compact – Cosmos can get a bit leggy and rangy – and ‘Picotee’ has delicate deep pink edging to white petals. ‘Seashells’ is a bit of an oddity, if you like something a bit unusual. Its petals are curled around on themselves, each forming a little trumpet like shape (or seashell like, I suppose). All cosmos have really lovely foliage, delicate, ferny and light, and it foliage can be picked and used as a foil to other flowers in flower arrangements. Basically they are just really easy, useful and pretty plants all round.
I am starting mine off by sowing them thinly into a seed tray, to save on space as the greenhouse starts to fill up with seedlings. A short row of each will do. Once they have germinated I will prick each seedling out into its own little pot and then grow them on until they are ready to go out. They want a sunny spot, and mine will be in two places, a row or two in the vegetable beds at the bottom of the garden, and then the others dotted around in the borders. They will also look beautiful in pots, and if I have enough I could imagine I might plant up two big pots of them to go either side of my garden path. They can be a little floppy for pots though, so it can be a good idea to push a shrubby branch such as you would use as a pea stick into the ground to support them. Or make sure you nip them out regularly, to encourage bushiness. Wherever you grow them they should reward you with a great number of high summer flowers for the border or the to sit prettily in a vase.