Hartley Magazine

All the latest news, hints, tips and advice from our experts

It may be December but there’s lots to do in the greenhouse

Start Amaryllis bulbs into growth, watering sparingly at first; just trickle a little tepid water around the bulb, then increase the amount as growth appears. Once they are actively growing, keep them constantly moist but not waterlogged and take care not to get the growth tip wet. They need temperatures around 20C so move them from the greenhouse to a warm sunny windowsill once temperatures drop (unless you have a heated greenhouse); keep room temperatures cool to prolong the flowering period (keep ‘Indian Azalea’s’, ‘Poinsettia’ and ‘Christmas cactus’ away from radiators too). Stake the flowering stems carefully to prevent it from falling over and rotate the pot a quarter of a turn each day, then sit back and enjoy the glorious trumpet flowers.

Open greenhouse vents for as long as possible on mild sunny days, shutting them before temperatures drop usually in early afternoon. High temperatures and low light encourage soft spindly growth and grey mould which spreads rapidly in cool, damp conditions. Air circulation can be maintained on cooler days with the help of a fan.

Christmas or Boxing Day are the traditional dates for sowing Onion seeds. Space them evenly over the surface of moist seed compost in trays or modules, and lightly cover with fine grade vermiculite. Put the tray in a heated propagator at 20C (70F) and they will germinate in 10-14 days. Grow them on in a cool greenhouse.

A healthy amaryllis bulb – the promise of fabulous flowers to come.

Keep an eye out for over-wintering aphids, whitefly, red spider mite and errant slugs hiding under pots and control them immediately. Continue successional sowing of salad leaves in pots and trays. Warming the compost in a heated propagator beforehand helps to speed up germination.

Wash labels in mild disinfectant, and stand the ends of bamboo canes used for tomatoes in mild disinfectant. Remove the names from plastic labels using a soft pan scourer and a little abrasive household cleaner.

In colder areas, on heavy, wet soils or where planting outdoors on ridges is not an option or where there is a short growing season, plant garlic in pots or modules. It needs a long growing season and period of chilling at around 0-10C, around 6 to 8 weeks then bring it into a cold greenhouse until next spring, water as it starts into growth and transplant when the soil dries out and growing conditions improve.

Keep greenhouse gutters free of leaves and debris and collect rainwater from the greenhouse roof.  During periods of heavy rain, don’t let the water in your butt overflow and go to waste, use it to water the soil at the base of walls in the ‘rain shadow’ of your house.

Sow any leftover peas into pots or deep trays of compost, about 5cm apart. Harvest the tips, with a pair of scissors in late winter or early spring, when they are two or three inches tall.  After harvesting, feed with general liquid fertilizer as a boost to produce more edible growth and harvest the shoots a few weeks later. Enjoy the festive season. Happy gardening. Matt.