A Greenhouse is an invaluable gardening tool, allowing you to circumvent seasonal limitations and extend your growing season throughout the year. Benefits include the ability to overwinter delicate plants, propagate seedlings and grow a variety of edibles – even in the winter months. To get the best of your Greenhouse in 2025, historic Greenhouse manufacturer Hartley Botanic has provided an overview of key jobs and tasks to do month by month, helping to ensure you maximise productivity and enjoyment.

JANUARY

As January progresses toward spring, there's a sense of optimism knowing the grey days are numbered, and soon seed sowing will begin in earnest.

It is not always practical to grow everything from seed, so make a list of plants you intend to sow and those to be bought as plug plants. Plug plants save time and space in the Greenhouse and heating costs, too.

Once you have placed your orders, write the labels for the seed trays, put them in alphabetical order and in an elastic band, then all you need to do is add the sowing date, later on.

Sow winter salads like lettuce and oriental veg in pots or trays of peat-free multipurpose with added John Innes compost. Keep the compost moist, but not waterlogged, and thin seedlings or provide ventilation to avoid problems with fungal diseases.

If you missed sowing broad beans in autumn, sow some now under glass for an early summer harvest, 5-8cm apart and 2.5cm deep in deep trays of peat substitute multipurpose compost or singly in small pots. Put them in a cool frost-free Greenhouse, and ‘harden off’ before planting outdoors in early spring. ‘The Sutton’ and ‘Robin Hood’ are both dwarf and ideal for windy sites; ‘Aquadulce’ and ‘Aquadulce Claudia’ are reliable elsewhere.

Water plants showing signs of drought giving them just enough to prevent desiccation, water in the morning so the compost is dry before evening; don’t splash water onto the leaves or into the crowns.

Jobs for January:

1. Make a list of plants you intent to sow, and those to be bought as plug plants.

2. Write labels for seed trays and put them in alphabetical order.

3. Sow winter salads like lettuce and oriental veg.

4. If you missed sowing broad beans in autumn, sow some now under glass for an early summer harvest.

5. Water plants showing signs of drought giving them just enough to prevent desiccation.

FEBRUARY

Plants like peppers, chillies, and aubergines, which require a long growing season, should be sown in February. The third week of February is ideal, mid-March is fine, and the first week of April is the latest. They need light, warm conditions, and constant temperatures for germination, so a propagator and supplementary lighting are useful, though not essential. Alternatively, you can buy young plants from a garden centre or online later in the year. After sowing seeds in a pot of peat free compost, cover with fine-grade vermiculite and place them in a propagator or warm spot. Once germinated and large enough to handle, transplant the seedlings into 9cm pots and grow on in the Greenhouse until they are ready for their final position.

February is also a great time to start tuberous begonias and propagate dahlias. For begonias, place tubers in seed trays, cover with a mix peat free multipurpose compost and keep them warm. When shoots appear, move them to a shaded area. For dahlias, place tubers in trays of peat free multipurpose compost and, once shoots appear, take cuttings to root in compost using hormone rooting powder. Keep sowing salads and forcing rhubarb, and start sweet peas and summer annuals like Cosmos. Clean the Greenhouse glass on a warm day with soapy water and disinfectant for better light and growth.

Jobs in February:

1. Sow peppers, chillies, and aubergines for a long growing season.

2. Start tuberous begonias in seed trays with warmth and shade.

3. Propagate dahlias by taking cuttings from new shoots.

4. Sow sweet peas, summer annuals, and "cut and come again" salads.

5. Clean Greenhouse glass with soapy water and disinfectant for improved light.

MARCH

At this time of year, a Greenhouse proves invaluable by extending the growing season. Sow celeriac, celery, lettuce, parsley, tomatoes, and French beans in pots, trays, or modules inside a propagator. Larger seeds like peas can be sown in peat free multipurpose compost, while smaller seeds like tomatoes and lettuce do best in seed compost. Warm compost bags in the Greenhouse for 24 hours or fill trays and warm them in the propagator before sowing. Also, warm a watering can of tap water in the Greenhouse beforehand, as chlorine acts as a fungicide. Before sowing, prepare the compost by removing any lumps, firming it down in the tray, and allowing it to drain after watering. Thinly sow seeds and use a mist sprayer for small seeds. Ventilate your propagator daily by removing the lid for half an hour, wiping off condensation.

Once seeds germinate, carefully 'prick out' or transplant seedlings into single pots or modules. Use a small tool to gently separate seedlings, ensuring minimal root disturbance, and transplant them into moist compost with 2.5-5 cm spacing. Growing in modules can eliminate the need for pricking out, as you can sow two or three seeds per module, then thin out the weaker seedlings. Tomatoes still need to be sown in a heated propagator, requiring temperatures between 15-20°C (60-70°F). Celery seeds, needing a minimum of 15°C, should be sown in late March, covered with a light layer of vermiculite or sieved compost to aid germination.

Jobs in March:

1. Sow tomatoes in a heated propagator.

2. Warm compost and water in the Greenhouse before sowing seeds.

3. Ventilate the propagator daily by removing the cover and wiping condensation.

4. Prick out or transplant germinated seedlings into pots or modules.

5. Sow celery seeds in late March, ensuring they receive light for germination.

APRIL

In April, sow celeriac, spinach, and turnip in modules early in the month, using peat-free seed or finely sieved multipurpose compost. Larger seeds like peas and beans can be sown directly in multipurpose compost. Tender plants, like cannas should be placed in the propagator to encourage early growth before hardening off and planting outside, ensuring there’s no risk of frost. Half-hardy annuals, including climbers like ‘Morning Glory’, can be sown after soaking the seeds in tepid water for 24 hours. These climbers need hardening off to prepare for transplanting, as they are sensitive to cold.

Ensure the Greenhouse is well-ventilated on warm days, using louvres or vents instead of opening the door to prevent drafts. Cover tender plants with fleece at night in an unheated Greenhouse and shade seedlings during the day to avoid scorching. Prick out peppers and aubergines into modules once the seed leaves have expanded, holding on to the leaf, not stem. Plant tomatoes, chillies, and aubergines in growing bags, ensuring proper drainage and adequate compost volume. Regularly damp down citrus plants when flowering begins, feed regularly with summer food from very early in the month and watch for pests like red spider mites and aphids, controlling them with environmentally friendly methods.

Jobs in April:

1. Sow celeriac, spinach, and turnip in modules.

2. Harden off tender plants before planting outside.

3. Ventilate the Greenhouse while avoiding drafts.

4. Prick out peppers and aubergines into modules.

5. Plant tomatoes, chillies, and aubergines in growing bags.

MAY

The ground outside can still be too cold and wet for direct sowing, making the Greenhouse a crucial space for May, so you can still get ahead. Seeds sown in trays last month will now need 'pricking out' into larger pots before their roots become tangles. Gently loosen the compost around each seedling with a dibber, lift by the first true leaf, and transfer to a new 9cm pot, planting slightly deeper than before. Water with tepid tap water initially, switching to rainwater once the plants are established. Ventilate the Greenhouse using roof and side vents. If you haven’t sown plants needing a longer growing season yet, it’s not too late to purchase plug plants of plants like chillies and aubergines for growing on.

‘Harden off’ young plants by placing them outdoors during the day and bringing them inside at night for 10-14 days, then leave them out overnight before planting. Cover with fleece on colder days. Water and feed tender plants, maintaining cooler temperatures to prevent spindly growth. Inspect plants daily for pests like aphids, whitefly, and red spider mites, using organic sprays and misting with tepid water to increase humidity. Planting French marigolds in the Greenhouse can deter whitefly and soil nematodes. There is still time to sow runner beans and squashes in pots to extend the cropping season.

Jobs for May:

1. Prick out seedlings into larger pots as they grow.

2. Ventilate the Greenhouse, avoiding cold drafts.

3. ‘Harden off’ young plants before planting outdoors.

4. Inspect daily for pests and control them early.

5. Sow more runner beans, squashes, or courgettes to extend the growing season.

JUNE

In June, there’s much to do in the Greenhouse. Transplant aubergines, peppers, and chillies into pots one or two sizes larger when their root systems are healthy but before they become pot bound. Use 23 cm pots or two per growing bag for final transplanting. Pinch out the tips of aubergines when they reach 30-40 cm tall and stake them as needed. For pollination, tap the flowers on sunny days around midday to mimic bee activity. Allow only five or six aubergines to form per plant. You can also transplant peppers and chillies into 23 cm pots, pinching the growing tips at around 15 cm to encourage branching and heavier cropping.

It’s not too late to sow sweetcorn using deep pots or recycled cups with drainage holes. In cooler areas, sow French and runner beans in root trainers and pumpkins in individual pots. Ensure good ventilation in the Greenhouse on hot days while avoiding chilling drafts, opening ventilation on the leeward side. As tomatoes grow, remove side shoots from cordon varieties to maintain a single productive stem, and tie them to supports. Do this weekly. Water crops regularly with tepid water, especially those in growing bags, to prevent issues like blossom end rot. Feed potted plants with liquid fertilizer, shifting to high potash tomato fertilizer as they establish. Finally, check daily for pests like whitefly and red spider mite, and harden off tender plants once frost risks have passed.

Jobs in June:

1. Transplant aubergines, peppers, and chillies into larger pots.

2. Sow sweetcorn and other seeds in deep pots or trainers.

3. Ventilate the Greenhouse while avoiding chilling drafts.

4. Remove side shoots from cordon tomatoes and tie them to supports.

5. Water crops regularly and monitor for pests.

JULY

In July, once tomatoes have set their fourth or fifth truss of fruit, cut off the main stem just above the terminal truss to focus moisture and nutrients on ripening. Tap open flowers around midday to encourage pollination and support the stems with ties or canes, ensuring they’re not too tight. In southern Britain, make a last sowing of runner and French beans indoors for early autumn crops, and also sow basil, coriander, dill, and Florence fennel in pots or modules for outdoor planting.

Twine cucumber stems around their supports and cut back side shoots beyond the flowers to improve airflow and reduce the risk of powdery mildew. Avoid wetting the leaves. Harvest cucumbers when they reach about 30 cm long.

Keep the Greenhouse clean by removing damaged or diseased material, and sweep the paths regularly to prevent pests and diseases. Early in the month move citrus plants outdoors to a sunny, sheltered spot, misting their leaves and watering them with tepid rainwater without allowing the pots to sit in water and continue feeding. Feed container plants with tepid water, checking moisture levels by assessing compost, if you stick your finger in the compost and pull it out and there are fragments stuck to your finger, it doesn’t need watering. For melons, pinch out growth beyond the fifth leaf while retaining the four strongest stems and pollinate female flowers with male ones to ensure good fruiting.

Jobs in July:

1. Cut off the main stem of tomatoes above the terminal truss.

2. Sow runner and French beans indoors for autumn cropping.

3. Support cucumber stems and cut back side shoots.

4. Remove damaged or diseased material from the Greenhouse.

5. Move citrus plants outdoors and feed container plants with tepid rainwater.

Bottom of Form

AUGUST

Blossom End Rot, where the end of tomatoes becomes black and flattened, also affects peppers, aubergines, squashes, and watermelons but is most common in tomatoes. It occurs due to a lack of calcium in the fruits, caused by poor water flow within the plant rather than a calcium deficiency in the soil. Plants in pots or growing bags with limited rooting space are more prone to this issue, especially in dry or acidic conditions. To prevent it, ensure consistent moisture and good ventilation for steady growth in the Greenhouse, watering twice a day if necessary. Growing in larger pots, border soil, or using mulches and automatic watering systems can help. Always apply liquid fertiliser to moist soil, and tomatoes with Blossom End Rot can still be eaten after removing the damaged part.

In August, continue sowing ‘cut and come again’ crops such as mixed herbs and salads in pots. Check for pests like red spider mites and whitefly on aubergines, peppers, cucumbers, melons, and chillies, using organic sprays or biological controls. Maintain high humidity for spider mite control and regularly reapply short-persistence environmentally friendly sprays for whitefly; even better, use biological controls. Ensure regular watering and ventilation, especially before temperatures rise, and let watering cans warm in the Greenhouse before use. Fruiting crops like cucumbers, aubergines, and tomatoes need consistent watering and weekly feeding with high potash fertiliser. Mist cucumber leaves or dampen the floor to increase humidity, and harvest crops regularly to enjoy the rewards of your efforts.

Jobs in August:

1. Prevent Blossom End Rot by maintaining consistent soil moisture and good ventilation.

2. Continue sowing herbs, salads, and leafy greens for later harvests.

3. Monitor aubergines, peppers, and cucumbers for red spider mites and whitefly, applying organic sprays as needed.

4. Water and ventilate regularly, ensuring watering cans are warmed in the Greenhouse before use.

5. Feed fruiting crops weekly with high potash fertiliser and increase humidity by misting or dampening the floor.

SEPTEMBER

Early in September, especially on warm and sunny days, sow trays, pots, or old growing bags with ‘cut and come again crops’ like land cress, pak choi, mizuna, mibuna greens, lettuce, lamb’s lettuce, chicory, and radish. You can also harvest earlier brassica sowings as microgreens. As temperatures drop, reduce watering and damping down, and take semi-ripe cuttings from tender plants like pelargoniums and salvias for overwintering. Towards the end of the month, start lifting and potting up tender plants for a frost-free Glasshouse along with divisions of chives, lemon balm, mint, and French tarragon to extend the cropping season.

Clean the outside of the Greenhouse on a warm autumn day with environmentally friendly detergents, rinsing with clean water. Use a broom for scrubbing and a pressure washer if available, while scraping moss from between overlapping panes with an old kitchen knife or credit card. Compost aubergines that have finished cropping to create more space and improve air circulation. Later in the month, remove unripe tomato trusses to ripen indoors or on the Greenhouse bench and replace them with winter crops. September is also the time to treat tender plants with biological control nematodes for vine weevil and check they are disease free - to avoid introducing pests and diseases into the Greenhouse over winter.

Jobs in September:

1. Sow ‘cut and come again crops’ for autumn and winter harvest.

2. Reduce watering and damping down as temperatures drop.

3. Take semi-ripe cuttings from tender plants for overwintering.

4. Clean the outside of the Greenhouse and remove moss.

5. Treat for vine weevil and eradicate pests before winter.

OCTOBER

Early October is the time to prepare your Greenhouse for the colder months. Begin by picking the last of your tomatoes, sweet peppers, and chillies, and ripen them on a sunny windowsill or in a paper bag with a ripe banana or pear, as the ethylene produced by the fruit helps with ripening. Blemish-free tomatoes can be stored in a cool drawer, checked regularly for decay, and spaced apart to prevent bruising, then ripening on a sunny windowsill or in the fruit bowl. After harvesting, tidy the Greenhouse by removing weeds and plant debris, and clean the glass inside and out using warm soapy water. Once cleaned, insulate the Greenhouse with bubble wrap or fleece, ensuring vents can still open. Check that your Greenhouse heater is working and consider having a backup heater on hand to avoid surprises when frost threatens.

Once the first frosts have blackened dahlias and other tender plants, cut back the foliage to within 5 cm of the base and cover the soil with a thick mulch of well-rotted organic matter in milder climates. In colder climates, lift and store the tubers of tender plants like dahlias and cannas in a cool, frost-free location, under the Greenhouse bench is ideal, ensuring labels stay with the tubers and that they drain properly. Bring tender plants such as fuchsias and pelargoniums into the Greenhouse, cutting back stems to save space and keeping them just moist over winter. Additionally, consider sowing sweet peas in October or November; germinate the seeds between damp kitchen towels for 48 hours before transplanting into deep pots or sections of cardboard to protect them from mice.

Jobs in October:

1. Pick and ripen the last tomatoes, sweet peppers, and chillies.

2. Clean the Greenhouse glass inside and out.

3. Insulate the Greenhouse with bubble wrap or fleece.

4. Cut back foliage of frost-affected plants and mulch the soil.

5. Lift and store tubers of tender plants in a cool, frost-free place.

NOVEMBER

Sow sweet peas in a cool Greenhouse for an early display next year by softening the seed coat. Place the seeds between two damp layers of kitchen towel for about 48 hours, then sow those that begin to swell or sprout in ‘Root Trainers’ or pots, covering them with compost. Keep them in a propagator at around 15°C (59°F) and, once germinated, overwinter the young plants in a cold frame or unheated Greenhouse. Continue to sow batches of winter salads weekly in an unheated Greenhouse, such as land cress, pak choi, and various greens, ensuring to ventilate the Glasshouse on dry days to prevent humidity-related issues like grey mould.

In November, you can also dig up and pot ‘Lily of the Valley’ rhizomes for forcing in the Greenhouse, which will bloom in spring. Transplant cuttings and seedlings into larger pots and keep them slightly moist over winter, covered with horticultural fleece for protection. Make your final harvest of Glasshouse crops like peppers and chillies, which can be dried for later use. Additionally, pot up chives, mint, and parsley, and bring them into the Greenhouse to continue growing through the winter, while alpine cushion plants should be kept dry to prevent rotting.

Jobs in November:

1. Sow sweet peas for an early display next year.

2. Continue sowing winter salads weekly in an unheated Greenhouse.

3. Dig up and pot ‘Lily of the Valley’ for forcing.

4. Transplant cuttings and annual seedlings into larger pots.

5. Make final harvests of Glasshouse crops like peppers and chillies.

DECEMBER

Now is the time to buy Amaryllis (Hippeastrum) to ensure festive blooms. Start them in the Greenhouse, watering sparingly at first, and bring them indoors as they grow. Once they are actively growing, keep the soil moist but not waterlogged, and avoid wetting the growth tip. Stake the stems to prevent them from toppling, and keep them in a warm spot at 60-65°F. Once indoors, maintain a cooler temperature to prolong flowering, the same applies to Indian Azaleas, Poinsettia, and Christmas cactus. Don't forget to remove houseplants from windowsills at night to protect them from cold damage.

Watch for pests like aphids, whitefly, and red spider mites, in the Greenhouse and remove any fallen leaves to add to your compost heap. Wash your pots and seed trays, stacking them for next year, and clean benches with a mild disinfectant. If you want to plant during the holiday break, sow onion seeds on Christmas or Boxing Day, using peat free compost covered with a layer of fine vermiculite and a heated propagator to aid germination. Plant garlic in pots for colder regions, allowing them to start in a cold Greenhouse. Lastly, open Greenhouse vents on mild days to prevent spindly growth and grey mould while avoiding chilly drafts.

Jobs for December:

1. Buy and start Amaryllis for indoor flowering.

2. Watch for and control overwintering pests like aphids and mites.

3. Clean and organize pots, seed trays, and benches.

4. Sow onion seeds on Christmas or Boxing Day.

5. Plant garlic in pots for a cold start and transplant in spring.