How To Plant A Greenhouse Vegetable Garden? | Pro Tips

Ready to grow reliable salads, herbs, and vine crops under cover? This guide walks you through planning, soil setup, temperature control, and a planting calendar that fits a small or mid-size structure.

Planting A Greenhouse Veggie Garden: Step-By-Step

Success starts with a layout you can reach and water without fuss. Build waist-high or knee-high beds, leave 18–24 inch walkways, and set one clear service lane for carts or hoses.

Choose Crops By Season Windows

Protected growing lets you start early and finish late, but crops still follow heat and light needs. Cool-season plants thrive in mild days and chilly nights. Warm-season plants want steady heat and are unhappy in cold soil. Grouping by these windows makes scheduling simple.

First 30% Reference Table: Crop Windows Under Cover

Match sowing and transplant timing to your climate and structure. Dates are general and shift with frost and day length.

Crop Group	Start Window	Notes
Leafy Greens (lettuce, spinach, chard)	Late winter–early spring; late summer–fall	Sow direct or in trays; harvest cut-and-come-again.
Brassicas (kale, broccoli, cabbage)	Late winter starts; set out early spring	Cool nights are fine; watch for aphids on soft tips.
Roots (radish, beet, carrot)	Early spring; late summer	Prefer loose, stone-free beds; keep evenly moist.
Alliums (green onion, leek)	Late winter trays; spring transplant	Slow starters; steady moisture helps uniform stalks.
Warm Vines (tomato, cucumber)	Start late winter indoors; set after frost	String trellis from roof bars; prune to 1–2 leaders.
Warm Fruit (pepper, eggplant)	Start late winter; set after nights stay mild	Need heat retention at night early in the season.
Herbs (basil, parsley, dill)	Spring through summer	Basil likes heat; parsley is flexible and slow.

Map Your Space, Beds, And Paths

Draw a quick plan with bed dimensions and aisle widths. Two rows of beds with a central walkway suit most hobby houses. Keep bed widths to 30–36 inches so every part is reachable from the edges. Deep, friable soil is the real upgrade indoors; it buffers moisture and roots dive fast.

Soil Mix That Drains Yet Holds Moisture

Blend screened compost, quality topsoil, and coarse material such as perlite or sharp sand. Aim for a crumbly texture that won’t puddle. If you garden on concrete or gravel, build 10–12 inch-deep raised beds or use large troughs. Refresh beds each cycle with compost and a balanced slow-release organic fertilizer, then side-dress heavy feeders midseason.

Set Up Irrigation Before You Plant

Drip lines or soaker hoses save time and keep leaves dry, which lowers disease pressure. Put a simple battery timer on the spigot. Start with short, daily runs for seedlings, then lengthen and reduce frequency as roots reach deeper. Do the finger-test two knuckles down; water when the top inch is dry but the root zone feels cool and slightly damp.

Dial In Air, Light, And Temperature

Indoor heat can build fast on sunny days. Passive roof vents and louvered side vents will dump heat if they have room to move. Clip-on fans even out pockets and keep leaves dry. Shade cloth in midsummer reduces leaf scorch and helps cucumbers and lettuce hold quality. For practical methods, see the RHS guidance on ventilation and shading.

Vent Targets That Keep Plants Comfortable

As a rule of thumb, start opening vents when inside air runs a few degrees above outdoors on sunny days. Mechanical guidance from university sources suggests planning for high air exchange: a fan capacity near 8–10 cfm per square foot can hold indoor air within about 5 °F of outside conditions on warm days. Install thermostats where sun doesn’t hit them directly for accurate control.

On spring nights, close up early to trap stored warmth. In winter, add a small heater with a safe thermostat if frost threatens tender crops. Many cool-season plants sail through light chills, but fruiting vines stall when nights stay cold.

Light And Spacing

Give seedlings strong light so they don’t stretch. In cloudy months, move trays to the brightest bay. Space transplants to the label recommendation; crowding cuts airflow and invites mildew. Trellis vines vertically to reclaim aisle space and lift fruit into clean air.

Planting Steps You Can Repeat Each Season

1) Pre-Plant Cleanup

Clear old roots, sweep paths, and scrub algae from glazing so light reaches beds. Disinfect shears and trellis clips with a mild bleach solution. Check that vents, fans, and timers are working before you sow the first tray.

2) Bed Prep

Loosen the top 6–8 inches with a fork, blend in compost, and level. Water the bed lightly so the surface settles. If you use a soil thermometer, wait to set tender plants until you see steady warmth at root depth.

3) Sowing And Transplanting

Direct-seed fast crops like radish and baby greens in bands. Start tomatoes, peppers, and herbs in cell trays, then transplant when roots knit the plug but haven’t spiraled. Water in gently to settle soil around roots.

4) Trellis And Prune

Run sturdy lines from roof purlins. Train tomatoes and cukes up twine, remove suckers on indeterminate tomatoes, and thin crowded leaves. Keep fruit off the floor with clips or slings where needed.

5) Water And Feed

Early on, water lightly and often; later, water deeper and less often. Feed heavy bearers with a soluble fertilizer every 10–14 days once flowering begins. Leaf crops prefer steady moisture over big gulps.

6) Scout Weekly

Check leaf undersides for aphids, whitefly, or mites. Remove yellow leaves, wipe algae from trays, and wash tools. Sticky traps near doors help you notice changes before they spread.

Pollination Inside A Closed Structure

Leafy greens and roots don’t care about pollinators for harvest, but fruiting vines do. Gentle shaking of tomato strings each day or a pass with an electric toothbrush at flowers moves pollen. Keep humidity moderate during flowering so blossom parts shed pollen cleanly.

Watering And Heat: What To Aim For

Every house and climate is different, so treat the numbers below as starting points. Watch your leaves and adjust. On blazing days, vent early and run fans.

Second-Half Reference Table: Comfort Targets

Stage	Day/Night Aim	Water Guide
Seedlings	60–70 °F days, 50–60 °F nights	Short, frequent pulses; avoid soggy flats.
Leaf Crops	60–75 °F days, cool nights ok	Keep root zone evenly damp.
Fruiting Vines	70–85 °F days, 60–70 °F nights	Deep water; reduce leaf wetness.
Cold Snaps	Protect from frost; close early	Water early in day; avoid night-wet foliage.
Heat Waves	Vent to near outdoor temps	Water mornings; use shade cloth.

Pests, Hygiene, And Crop Rotation Indoors

Cleanliness is your best tool under cover. Sweep paths, empty old pots, and keep plant waste out of the house. Rotate beds even inside a small footprint: move tomatoes and peppers each cycle, then backfill with greens or roots. This breaks pest and disease cycles and balances nutrient draw.

Simple Integrated Practices

• Quarantine new starts for a week before adding to main beds.
• Vent early to lower humidity swings.
• Water at the base, not over the canopy.

Calendar You Can Follow

Late Winter

Sow cool greens, brassicas, and scallions in trays. Start tomatoes and peppers on heat mats if you grow long-season types. Fix any leaky fittings and test thermostats.

Spring

Transplant into beds as day length rises. Add strings and clips for vines. Start cucumbers when nights feel steady and soil reads warm at depth.

Summer

Run shade cloth in the hottest stretch. Keep vents propped and fans on. Sow basil every few weeks for fresh leaves. Watch for spider mites during dry spells.

Fall

Pull warm crops as productivity wanes. Refill beds with leafy mixes and quick roots. Patch tears in plastic before storms. Close up earlier in the evening to bank heat.

Winter

Harvest salads and baby roots as growth slows. Keep irrigation light but steady. Scrub algae, oil latches, and plan the next rotation.

Gear That Pays Off

You don’t need a gadget wall. A short list covers the essentials: a max-min thermometer, a simple timer, two clip-on fans, shade cloth, sturdy trellis twine, and a hose-end filter if your water is hard. Add a compact heater only if frosts are regular and you plan to carry warm crops through shoulder seasons. Label valves and timers so any helper can keep irrigation on schedule every day.

When To Vent And How Much

Open early on bright days. Roof vents dump heat fast; side vents feed cooler air at plant level. If your house runs hot, add an extraction fan sized to your floor area and a louver opposite to pull air across the canopy.

Common Mistakes To Dodge

Packing Beds Too Tightly

Overcrowded plants sit wet and invite mildew. Give each variety the spacing on its tag, and prune vines weekly.

Letting Humidity Swing

Big swings stress leaves and trigger botrytis on dense canopies. Vent in the morning, water earlier in the day, and keep air moving at dusk.

Planting Warm Crops Into Cold Soil

Tomatoes and peppers stall when roots are chilly. Wait for steady warmth at root depth, then transplant.

Skipping Sanitation

Dirty tools and algae-slick floors spread problems. Rinse paths, wash hands or gloves between beds, and dump diseased foliage outside the house.

Wrap-Up: A Simple, Repeatable System

Plan by season, prep deep beds, set ventilation and drip before planting, trellis early, and scout weekly. With steady routines, you’ll harvest greens most months and carry vines through the sunny stretch with less effort.