The Glass Tells First: A Winter Morning in an Unheated Cornish Greenhouse

The first look, before the kettle

Elowen doesn’t switch the light on straight away. The greenhouse has no light to switch on, only a torch that lives in the door pocket and a window that has fogged itself into a soft grey square. It is just after eight, the Camel valley is still half-asleep under a low, drizzly sky, and the glass is doing what glass does in a Cornish November: holding the morning’s breath.

She calls it the fog check. Not watering, not potting on, not the satisfying business of moving things around. Just looking. The kettle can wait. The greenhouse, she says, has already been up for hours.

This is the quietest part of the growing year, but it is also the part where small mistakes get expensive. A sealed greenhouse feels kind in November and turns punishing by January. A wet pot forgotten in a corner can take a tray of cuttings with it. The clues are nearly always on the inside of the glass, if anyone bothers to read them.

What the fog is saying

On this morning the roof panes are heavily beaded, with one long drip gathering above the path and falling with a soft, irregular tick into a bucket Elowen has left there on purpose. The upper vents are closed. The door has been shut since yesterday afternoon. The first thing she notices is not the wet but the pattern of it.

Condensation on the roof is normal. It is the greenhouse equivalent of a kettle boiling: warm, damp air from the soil and the plants meets cold glass and gives up its moisture. What matters is where the water goes next. If it drips onto leaves and sits there, that is a problem. If it runs down the frame and into the gravel, that is a system working.

She runs a finger along the aluminium gutter and finds it clear. The bucket has an inch of water in it. That is a good sign. The bad sign is the back corner, where a sheet of bubble wrap has come loose and the glass behind it is running with water. The bubble wrap is doing its job of insulation, but it has also created a pocket where the air has stopped moving. The compost in the pots below is darker than it should be.

“People think winter watering is about giving less,” she says, tipping a small pot to feel its weight. “It is really about giving less often and noticing more. A soggy pot in November is often a pot that was watered in October and never checked again.”

Damp corners, dry corners

A greenhouse is never one climate. Elowen’s is a lean-to against a stone wall, about twelve feet by eight, with a gravel floor and a bench that has been repainted so many times it has a soft, rounded edge. The wall side stays warmer. The door end stays colder. The corner nearest the water butt is the damp one, always. The corner behind the potting bench is the dry one, sometimes dangerously so.

She keeps a cheap hygrometer on the bench, but she trusts her hands more. The dry corner is where the terracotta pots feel light and the leaves of a bay tree are turned slightly inward. The damp corner is where a tray of pelargonium cuttings has begun to look pale and soft at the base. That is not cold damage. That is the beginning of something fungal, and it has been helped along by still, wet air.

The fix is not a heater. It is a gap. She opens the door a few inches and props it with a brick. Within ten minutes the roof stops dripping quite so enthusiastically. The bubble wrap is reattached with a couple of plastic clips, leaving a small channel behind it so air can move. The pelargonium tray is moved to the bench, where the light is better and the air is less crowded.

Airflow without the draught

This is the balance every unheated greenhouse keeper learns, usually the hard way. Seal everything and you get mould, damping off and a smell that is somewhere between wet newspaper and old compost. Open everything and you get a cold, wet gale funneling through the ridge, which is worse for tender plants than a still, chilly night.

Elowen’s rule is simple: move air, not weather. On a mild, mizzly morning like this one, the door stays open for an hour after breakfast. On a clear, frosty morning, it stays shut until the sun has had a chance to warm the ridge, and then the vent opens for twenty minutes. If the forecast is for a Cornish special — driving rain and a north-easterly — everything is closed and she spends the time checking pots instead.

She has no automatic vent opener on this greenhouse. She had one once and it failed in a way that left the vent open during a February gale. Now she uses her hands and a small notebook. The notebook is not a weather diary, exactly. It is a fog diary. Roof heavy, door end dry, back corner wet, lemon verbena looking sulky. A few lines a day. By February it is a record of what her greenhouse does, not what the internet says a greenhouse should do.

The plants that tell you first

The tender things are the honest ones. A lemon verbena will drop its leaves at the first hint of cold roots. A fuchsia will go limp before it goes black. The pelargoniums, overwintered on the dry side of the bench, are slower to complain, which is why Elowen checks their compost by weight every few days. Light pot, water. Heavy pot, wait.

She overwinters a few agapanthus in pots against the house wall, not in the greenhouse, because they prefer the cold and the shelter. The greenhouse is for the plants that need the glass: a scented geranium, a small citrus, a tray of cuttings taken in September, a pot of parsley that has become a pet. Nothing exotic. Nothing that needs heat. The aim is not to keep them growing. The aim is to get them through.

“You can’t fight a Cornish winter with a paraffin heater and a closed door,” she says. “You just make a slightly kinder pocket of air and keep it honest. If the glass is dripping, something is too wet or too still. If the glass is dry, something is too dry. It is not complicated. It is just easy to ignore.”

A small routine for a small glasshouse

The fog check takes about ten minutes. Look at the roof. Look at the corners. Feel two or three pots. Open the door or vent if the air is still and the morning is mild. Close it again before the temperature drops. Move anything that is sitting in a drip. Pick off the yellowing leaves before they become a nursery for mould. Write one line in the notebook.

That is it. No grand scheme, no heated propagator, no expensive kit. Just a grower, a torch and a pane of fogged glass that has been quietly reporting the truth all night. On the way out, Elowen wipes a clear patch in the window with her sleeve and looks at the valley. The drizzle has thinned. The kettle is still waiting. The greenhouse, for now, is saying that everything is about right.