Not often considered a greenhouse plant, more one for the dappled shade garden or semi-wild rockery. Yet since Victorian times Lily of the valley has been grown in tubs under cover, both for it’s beauty in foliage, flower and perfume and for a cut flower for the house.
You might grow Convallaria from seed, it is not difficult and you should get flowers within three or four years. It’s the budded roots that are commonly sold like bulbs but these can be a bit difficult to establish. So for really reliable plants I’d choose pot grown specimens if possible despite the cost- and they will multiply fairly quickly given space.
If, as is so often the case only the budded roots can be got then as soon as these arrive give them a brief soak in rain water and then plant them up immediately. Pot the roots just below the surface with the pointed buds sticking up and into a loam based John Innes potting compost (or a multi-purpose mixed 50:50 with well-rotted grass turves) enriched with copious amounts, up to a third, of well rotted leaf mould.
Use large pots with plentiful drainage and make sure their compost is kept moist while the plants settle in. I also mulch over the compost in the tubs with a thick layer of chunky composted bark which helps to keep the roots cool.
Once established and growing away you can keep Convallaria permanently in your greenhouse in almost any convenient shady place where otherwise only a fern might survive such as under the staging. Then you can move the pot into a sunnier warmer place in late winter or early spring to bring the flowers into much earlier bloom and return it to the shady ‘winter quarters’ after. Or indeed the tub can go outside after flowering or cutting and stay there until brought in for forcing again the following spring.
Overall there is much to be said for keeping it under cover because Convallaria is undemanding and the foliage is so attractive anyway. What you can’t do easily is keep it in full sun under cover year round when the leaves will just parch and probably succumb to a red spider mite infestation. In order to prevent this it’s sensible to syringe the plants down frequently with rain water and add a little seaweed solution occasionally as this will be beneficial but do not feed except perhaps a spring tonic before flowering commences.As well as the common, delicious, white lily of the valley there is a larger taller ‘Bordeaux’ variety which is bigger but a tad coarser. There’s also a pink flowered variety and sadly currently lost to us there once was a red. And a clever idea the Victorians came up with- grow Lily of the valley in hanging baskets, true these need a lot of watering and the main show is over after a fortnight but how spectacular these were both under cover and when set outdoors.