April Gardening Jobs: What to Do in the Garden and Greenhouse
April brings longer days and warmer soil but frost remains a real risk until mid-May across most of the UK. Harden off seedlings started in March by placing them outdoors during the day and bringing them back under cover at night for 7-10 days. Direct sow carrots, beetroot, peas and broad beans outdoors once soil reaches 7°C. Keep greenhouse vents open during the day and closed at night to manage the 5-25°C temperature swings we see every April.
April is the month that makes or breaks your growing season. After 16 years of installing and working with greenhouses across the UK, I can tell you that the gardeners who get the most from their greenhouses in summer are the ones who put in the work now. Soil temperatures hit 7-10°C this month, vents need daily attention, and every seedling you harden off properly now will outperform one planted straight from the greenhouse by 2-3 weeks of cropping time.
Key Takeaways
- Harden off seedlings over 7-10 days before planting out - skipping this step costs 2-3 weeks of growth
- Greenhouse temperatures swing 20°C in a single day - fit an automatic vent opener or check vents twice daily
- Direct sow 8 vegetable crops outdoors including carrots, beetroot, peas, broad beans, spinach, radish, lettuce and spring onions
- Apply nitrogen-rich lawn feed in early April when soil hits 8°C and grass is actively growing
- Sow tomatoes, cucumbers, peppers and aubergines under glass at 18-21°C for planting out in late May
- Deadhead spring bulbs but leave foliage for 6 weeks to feed the bulb for next year's display
Installer's Note
April is when greenhouse temperatures swing wildly. We have measured 25°C at midday and 5°C by midnight in the same greenhouse. Without an automatic vent opener, you are gambling with your seedlings every time you leave the house. We fit more auto vents in April than any other month. A £25-35 autovent pays for itself in the first week by preventing heat stress that stunts tomato and pepper seedlings permanently.
What to Sow and Plant in April
April is the busiest sowing month of the year. Soil temperatures finally reach the 7-10°C range that most vegetable seeds need to germinate reliably. I keep a soil thermometer in my raised bed and only sow once it reads consistently above 7°C at 10cm depth for three consecutive days.
The table below shows every crop you can sow or plant in April, split by where to grow them. Use it as your weekly planner.
| Crop | Where to Sow | Soil/Compost Temp | Depth | Spacing | When in April |
|---|---|---|---|---|---|
| Carrots | Direct outdoors | 7°C+ | 1cm | 15cm rows, thin to 5cm | Early-mid |
| Beetroot | Direct outdoors | 7°C+ | 2.5cm | 30cm rows, thin to 10cm | Early-mid |
| Peas | Direct outdoors | 7°C+ | 5cm | 10cm apart in double rows | Early |
| Broad beans | Direct outdoors | 5°C+ | 5cm | 23cm apart in double rows | Early |
| Spinach | Direct outdoors | 7°C+ | 2.5cm | 30cm rows, thin to 15cm | Throughout |
| Radish | Direct outdoors | 5°C+ | 1cm | 15cm rows, thin to 2.5cm | Throughout |
| Lettuce | Direct or greenhouse | 7°C+ | 0.5cm | 25cm apart | Throughout |
| Spring onions | Direct outdoors | 7°C+ | 1cm | 1cm apart in rows | Throughout |
| Tomatoes | Greenhouse only | 18-21°C | 0.5cm | Individual 9cm pots | Early-mid |
| Cucumbers | Greenhouse only | 20-25°C | 1cm | Individual 9cm pots | Mid-late |
| Peppers & chillies | Greenhouse only | 18-21°C | 0.5cm | Individual 9cm pots | Early |
| Aubergines | Greenhouse only | 21-25°C | 0.5cm | Individual 9cm pots | Early |
| Runner beans | Greenhouse (plant out May) | 12°C+ | 5cm | Individual 9cm pots | Mid-late |
| Courgettes | Greenhouse (plant out May) | 15°C+ | 2.5cm | Individual 9cm pots | Mid-late |
| Second early potatoes | Direct outdoors | 7°C+ | 10-12cm | 30cm apart, 60cm rows | Early |
| Maincrop potatoes | Direct outdoors | 7°C+ | 10-12cm | 38cm apart, 75cm rows | Mid-late |
| Onion sets | Direct outdoors | 5°C+ | Just below surface | 10cm apart, 30cm rows | Early |
For a continuous harvest, sow salad crops every 2 weeks rather than all at once. I sow a short row of lettuce, radish and spring onions on the 1st and 15th of every month from April to August. This gives me fresh salads all summer without waste.
If you are growing tomatoes in a greenhouse, April is the ideal sowing month. Sow into modules at 18-21°C and pot on into 9cm pots when the first true leaves appear. They will be ready for their final positions by late May.
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April Greenhouse Jobs
Your greenhouse becomes the engine room of your garden in April. Proper management this month determines your entire summer harvest. After installing over 4,000 greenhouses, I know exactly what makes the difference between a productive greenhouse and a frustrating one.
The single most important job is ventilation. April sun through glass can push temperatures above 30°C by midday, then drop below 5°C overnight. That 25°C swing stresses seedlings and causes leggy, weak growth. An automatic vent opener solves this without you needing to be there.
Organise your greenhouse staging so tender seedlings sit on the top tier (warmest) and hardier crops go lower. I use the floor level for trays that are hardening off - they get the coolest temperatures and adjust gradually.
If you have not already cleaned your greenhouse, do it now. I wash every pane inside and out with a mild disinfectant solution. Clean glass transmits 15-20% more light than dirty glass, and that makes a visible difference to seedling growth rates. Check our guide on common greenhouse growing mistakes for more on this.
| Greenhouse Task | When in April | Why It Matters | Equipment Needed |
|---|---|---|---|
| Clean glass inside and out | Week 1 | 15-20% more light transmission | Greenhouse cleaner, soft brush |
| Fit or check automatic vent opener | Week 1 | Prevents 30°C+ heat damage | Autovent system |
| Sow tomatoes, peppers, aubergines | Week 1-2 | 8-10 weeks to planting-out size | Seed trays, fresh compost, labels |
| Prick out and pot on seedlings | Week 2-3 | Prevents root binding and leggy growth | 9cm pots, potting compost |
| Check min/max thermometer daily | Throughout | Spot dangerous temperature swings | Min/max thermometer |
| Water seedlings with room-temp water | Throughout | Cold water shocks roots | Watering can filled the night before |
| Check for whitefly, aphids, red spider mite | Weekly | Early treatment prevents infestations | Yellow sticky traps, biological controls |
| Begin hardening off March-sown seedlings | Week 3-4 | Prepares plants for outdoor conditions | Cold frame or sheltered patio spot |
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Matt's Pick for April GrowingBest For: Serious vegetable growers who need reliable ventilation and space for staging Why I Recommend It: The Venus 5000 has the widest opening roof vent of any 8x6, and I have fitted hundreds. The extra headroom means tomatoes reach full height without hitting the ridge bar. It handles April temperature swings better than any greenhouse in its class. Price: From £649 |
Lawn Care in April
April is when your lawn wakes up properly. Soil temperatures reach 8°C and grass starts growing fast. Get the timing right now and you will have a thick, weed-resistant lawn all summer.
Start with a light rake to pull out moss and thatch. Then give the lawn its first proper mow with blades set high at 4cm. Cutting too low too early stresses the grass and opens gaps for weeds. I drop the height by 0.5cm each fortnight until reaching my summer cutting height of 2.5-3cm.
Apply a spring lawn feed high in nitrogen (look for an NPK ratio like 12-5-5) in early April when grass is actively growing. Water it in if no rain falls within 48 hours. A single spring feed makes more difference than anything else you do to your lawn all year.
| Lawn Task | When | How | Frequency |
|---|---|---|---|
| Rake out moss and thatch | Early April | Spring-tine rake, firm strokes | Once |
| First mow at 4cm height | When grass reaches 5-7cm | Sharp blades, collect clippings | Weekly from now |
| Apply spring lawn feed (NPK 12-5-5) | Early April | Spreader or by hand, water in if dry | Once |
| Repair bare patches | Early-mid April | Rake area, scatter seed mixed with compost, water daily | Once |
| Edge borders | Mid April onwards | Half-moon edger for clean lines | Fortnightly |
| Treat broadleaf weeds | Late April | Spot-treat with selective weedkiller when weeds are growing | As needed |
Matt's Installation Tip
If you have a greenhouse on grass, the mower cannot reach the 15-20cm strip along the base. I see this create a weed jungle every April. Lay a 30cm gravel strip around the greenhouse perimeter - it stops weeds, improves drainage, and makes the whole area look tidier. We recommend this on every installation.
Hardening Off: The Step Most Gardeners Rush
Hardening off is the process of gradually acclimatising greenhouse-raised seedlings to outdoor conditions. It takes 7-10 days and most gardeners try to do it in 2. The result is stunted, stressed plants that take weeks to recover.
Here is the schedule I follow every year:
| Day | Daytime | Night | What to Watch For |
|---|---|---|---|
| Day 1-2 | Place outside in sheltered, shaded spot for 2-3 hours | Back in greenhouse | Leaf scorch from direct sun |
| Day 3-4 | Outside in partial sun for 4-5 hours | Back in greenhouse | Wind damage on tender stems |
| Day 5-6 | Full sun exposure for 6-8 hours | Back in greenhouse or cold frame | Wilting in afternoon heat |
| Day 7-8 | Outside all day in full conditions | Cold frame with lid closed | Night temperatures below 5°C |
| Day 9-10 | Outside all day | Cold frame with lid propped open | Ready to plant out if frost-free |
A cold frame makes hardening off much easier. It gives you a halfway house between greenhouse and open ground. I use mine constantly from April through May.
Matt's Tip: Frost Protection
Keep horticultural fleece ready throughout April. The Met Office issues frost warnings 24-48 hours ahead. I check the forecast every evening and throw fleece over anything tender if temperatures are dropping below 2°C. One night of frost can kill a month's work. I have seen it happen to customers who planted out too early without protection.
Flowers and Borders in April
Your borders should be buzzing with spring colour in April. Daffodils, tulips, and hyacinths are at their peak. The key job now is deadheading spent flowers while leaving the foliage intact for at least 6 weeks. The leaves feed the bulb underground and determine next year's display.
April is also the month to plant summer-flowering bulbs. Dahlias, gladioli, and lilies all go in now. I start dahlias in pots in the greenhouse to give them a 3-week head start, then plant out after the last frost. For direct planting, set dahlia tubers 10-15cm deep and 60cm apart.
Divide overcrowded perennials now while they are in active growth. I split hostas, heleniums, and geraniums by lifting the clump with a fork, dividing with a sharp spade, and replanting immediately. Water well after dividing. Read our guide on setting up a new greenhouse if you want to start flower seedlings under glass.
Week-by-Week April Planner
Use this weekly breakdown to stay on top of every April job without feeling overwhelmed.
| Week | Greenhouse | Vegetable Garden | Lawn & Borders |
|---|---|---|---|
| Week 1 | Clean glass, check vents, sow tomatoes and peppers | Direct sow peas, broad beans, radish. Plant onion sets and second early potatoes | First mow at 4cm. Rake out moss. Apply spring feed |
| Week 2 | Sow cucumbers, aubergines. Pot on March seedlings | Direct sow carrots, beetroot, spinach, lettuce. Plant maincrop potatoes | Deadhead spring bulbs. Divide perennials. Start weeding |
| Week 3 | Prick out seedlings. Sow runner beans and courgettes. Check for pests | Thin early sowings. Earth up potatoes. Succession sow salad crops | Mulch borders (5cm layer). Plant summer bulbs. Set up supports |
| Week 4 | Begin hardening off. Prepare hanging baskets (keep under glass until May) | Continue succession sowing. Feed fruit trees. Protect blossom from frost | Edge borders. Prepare containers. Check for pests |
Pruning Jobs for April
Spring-flowering shrubs like forsythia, flowering currant, and weigela should be pruned immediately after their flowers fade. Remove one-third of the oldest stems at the base to encourage fresh growth. Do not prune them before flowering or you will cut off this year's blooms.
Roses need a final check. Hybrid teas and floribundas should have been pruned in March, but remove any frost-damaged tips now. Cut to an outward-facing bud, about 5mm above. For climbing roses, tie in new growth and remove only dead or damaged wood.
Evergreen hedges can have a light trim in late April to tidy the shape before the nesting season (avoid heavy cutting from March to August to protect nesting birds). Deciduous hedges like beech and hornbeam get their first cut now.
Read our greenhouse ventilation guide for more on keeping air moving around plants - good airflow is as important as good pruning for preventing disease.
"April is the month I look forward to most. After 16 years of installing greenhouses and helping customers get the best from them, I still get excited when the first tomato seedlings emerge. The work you put in this month sets up everything that follows. Get your ventilation right, harden off properly, and do not rush planting out. The greenhouse is your best tool in April - use it."
- Matt W, Greenhouse Stores
Frequently asked questions
What can I sow directly outdoors in April?
Sow carrots, beetroot, peas, broad beans, spinach, radish, lettuce and spring onions directly outdoors in April. Wait until soil temperature reaches 7°C at 10cm depth. Use a soil thermometer rather than guessing. Most of these crops germinate in 10-14 days at the right temperature. Sow in short rows every 2 weeks for continuous harvests through summer.
When should I start tomatoes in the greenhouse?
Sow tomato seeds in early to mid-April at 18-21°C. They need 8-10 weeks from sowing to reach planting-out size, which puts them ready for late May or early June transplanting. Sow into modules or small pots of fresh seed compost and keep them on warm greenhouse staging close to the glass for maximum light.
How do I harden off seedlings properly?
Harden off over 7-10 days by gradually increasing outdoor exposure. Start with 2-3 hours in sheltered shade on day one. Increase to full sun by day five. Leave outside overnight by day eight, using a cold frame for protection. Never skip this step - seedlings planted straight from greenhouse to open ground suffer transplant shock and lose 2-3 weeks of growth.
What temperature should my greenhouse be in April?
Aim for 18-21°C during the day and above 5°C at night. April temperatures inside a greenhouse can swing from 5°C at dawn to 30°C by midday. An automatic vent opener manages this without you being present. Check a min/max thermometer every morning to spot dangerous overnight drops.
Is it too late to plant potatoes in April?
No, April is the ideal month for second early and maincrop potatoes. Plant second earlies in early April at 30cm spacing and 10-12cm deep. Maincrop varieties go in from mid to late April at 38cm spacing. Earth up shoots when they reach 10cm tall. Both types harvest from July onwards.
Should I mow my lawn in April?
Yes, give your lawn its first proper mow when grass reaches 5-7cm tall. Set the mower blade high at 4cm for the first cut. Cutting too short too early stresses the grass and encourages weeds. Drop the cutting height by 0.5cm every fortnight through spring. Apply a nitrogen-rich spring feed (NPK 12-5-5) in early April for the best results.
How do I protect plants from late frosts in April?
Keep horticultural fleece ready and check the forecast every evening. Cover tender plants with fleece when temperatures are forecast to drop below 2°C. Move pots into the greenhouse or against a south-facing wall overnight. Late frosts can occur throughout April and into mid-May across most of the UK. One frost can destroy an entire season of tender seedlings.
