January
Written by Michelle Jenkins
January Greenhouse Growing Guide – Michelle Jenkins
January is the perfect month to prepare your greenhouse for the year ahead. With a bit of care and planning, you can create an organised and productive growing space. Here’s my comprehensive guide to help you grow and maintain your greenhouses this winter.
Preparing A Greenhouse for Spring and Essential Maintenance
Clean and Refresh: Clean your greenhouse inside and out using warm, soapy water. This removes dirt, algae, and pests, while allowing maximum light to reach your plants during the shorter days of winter.
Organise supplies: Check your pots, shelving, trays, labels, and benching. Clean them thoroughly to avoid disease and prepare them for sowing. Take this time to stock up on essentials like seeds and compost.
Review heating and insulation: Aim to maintain a minimum greenhouse temperature of 5–7°C (42–45°F). Frost-sensitive plants may need extra protection on cold nights; horticultural fleece, straw, or even newspaper can provide a buffer against frost. Install a min-max thermometer to monitor temperature fluctuations.
Ventilation: Proper airflow is crucial even in winter. Open vents on dry, sunny days to prevent condensation and fungal diseases. Avoid ventilating during damp or foggy weather, and be sure to close vents mid-afternoon to retain warmth before nightfall.
Inspect equipment: Check heaters, fans, and propagators to ensure they’re in good working order. Replace or repair faulty equipment now to avoid interruptions during the growing season.
Crops and Flowers to Start in January
January is a great time to sow seeds under cover early, giving plants a head start for the spring.
Vegetables to Sow in January
Salad greens: Lettuce and pak choi can be sown year-round for a continuous harvest.
Root vegetables: Early beetroot and carrots germinate well in a greenhouse, producing tender, crisp crops.
Warm-season crops: Use a heated propagator to start peppers, aubergines, and tomatoes, maintaining a temperature of 21–24°C.
Flowers to Sow in January
Flowers bring beauty, support biodiversity, and make excellent companion plants for vegetables by deterring pests and attracting pollinators.
Sweet peas: Sow in long root trainers or toilet roll tubes for their deep roots.
Pelargoniums: Start in a heated propagator at 21–24°C. After germination, lower temperatures to above 8°C. Expect blooms by June.
Antirrhinums (Snapdragons): These need bottom heat to germinate. Once sprouted, keep them in a frost-free greenhouse.
Hollyhocks: Edible and beloved by pollinators, hollyhocks germinate best at 16–21°C.
Additional Tips for a Productive January
Plan your year: Use the quieter month to decide what you want to grow and organise your greenhouse layout for efficiency.
Prepare propagators: Test and clean your equipment so it’s ready for action when sowing starts in earnest.
Think long-term: January is a great time to start perennial flowers or crops that require longer growing periods, giving them a strong foundation for the year ahead.
Thanks for reading our guide on preparing your greenhouse for spring! With the right preparation now, your greenhouse will be set up for a productive growing season ahead. Whether you’re starting early seedlings, improving ventilation, or organising your space, these steps will set you up for success.
Want to stay ahead? Take a look at what’s coming up in February’s growing guide.
FAQs: January Growing Guide
January gives you space to get everything in order before the growing season begins. There’s less pressure to keep up with active crops, which makes it easier to focus on cleaning, organising, and planning properly.
A well-prepared greenhouse doesn’t just look better, it performs better. Clean glass improves light levels, organised benching improves workflow, and checking equipment now avoids problems later when plants are more vulnerable.
Cleaning isn’t just about appearance, it directly affects plant health. Dirt, algae, and leftover debris can harbour pests and diseases that quickly spread once new growth begins.
A proper clean should cover all key areas:
- glass to maximise light during shorter days
- benches, trays, and pots to remove contamination
- corners and frames where pests can hide
Starting with a clean environment reduces problems before they even begin.
Maintaining a stable minimum temperature is more important than trying to keep the space warm all the time. For most setups, around 5–7°C is enough to protect hardy plants and prevent frost damage.
More sensitive plants may need additional insulation or protection during colder nights. Monitoring temperature fluctuations with a thermometer helps you respond to changes rather than guessing.
It might seem counterintuitive, but ventilation is just as important in winter as it is in summer. Without airflow, moisture builds up quickly, creating the perfect conditions for mould and fungal disease.
Opening vents on dry, mild days helps regulate humidity and keeps the environment balanced. The key is timing, ventilate during the day, then close everything before temperatures drop in the evening.
January isn’t about high-output growing, but there are still opportunities to get ahead, especially under cover.
You can start:
- salad crops like lettuce and pak choi for steady harvesting
- early root vegetables such as beetroot and carrots
- warm-season crops like tomatoes, peppers, and aubergines with heat
These early sowings give you a head start, but only if conditions are controlled properly.
For many early crops, especially warm-season vegetables, consistent heat makes a big difference. Seeds like tomatoes and peppers require higher temperatures to germinate reliably.
While it’s possible to improvise with warmer spots or covered trays, a heated propagator provides stable conditions that improve success rates. It’s less about speed and more about consistency at this stage.
January is one of the few points in the year where you can step back and look at the whole growing season ahead. Once spring arrives, everything speeds up and decisions become more reactive.
Taking time now allows you to:
- decide what crops and varieties to grow
- organise your greenhouse layout for efficiency
- make sure you have seeds, compost, and equipment ready
A clear plan reduces wasted space, time, and effort later on.
The biggest mistake is treating January like an active growing month rather than a preparation phase. Trying to do too much too early often leads to weak plants and unnecessary work.
Other common issues include:
- overwatering when plants need very little
- poor ventilation leading to damp conditions
- starting seeds without enough light or heat
Keeping things simple and focused on preparation usually leads to better results when the season properly begins.
