Full Lifecycle

Overview of the Growing Cycle

Growing vegetables from seed in plastic bags involves several distinct stages. Understanding each stage helps you anticipate what the plant needs at any given point and respond to changes effectively.

Small seeds beginning to germinate in a plastic bag with moist soil
Early germination: the seedling emerges from the soil within 5–14 days depending on variety
A person carefully transplanting a seedling from a small pot into a larger plastic grow bag
Transplanting seedlings into prepared grow bags at the correct stage

Stage 1: Sowing Seeds

Seeds can be sown directly into prepared grow bags, or started indoors in small seed trays and later transplanted. Direct sowing is simpler but requires managing multiple seedlings per bag initially. Starting in trays allows you to select the strongest seedling before committing it to a bag.

Direct Sowing

  1. Fill the bag with prepared soil mix and moisten thoroughly
  2. Create a small indentation in the soil (depth specified on seed packet)
  3. Place 2–3 seeds per planting point to account for non-germination
  4. Cover lightly with soil and press gently
  5. Label the bag with variety and sowing date
  6. Keep soil consistently moist (not saturated) until germination

Starting in Seed Trays

  1. Fill small seed cells or trays with seed-starting mix
  2. Sow one seed per cell at the specified depth
  3. Keep in a warm location (18–24°C is suitable for most vegetables)
  4. Cover with a clear lid or plastic wrap to retain moisture during germination
  5. Remove cover once seedlings emerge
  6. Grow seedlings under adequate light until they have 2–3 true leaves before transplanting
Vegetable Germination Temperature Days to Germination Sowing Method
Tomato 20–25°C 7–14 days Start in trays
Pepper 22–28°C 10–21 days Start in trays
Lettuce 15–20°C 4–7 days Direct or trays
Radish 10–20°C 3–5 days Direct sowing
Cucumber 20–25°C 5–10 days Start in trays
Spinach 10–18°C 7–14 days Direct sowing
Tip — Thinning

If multiple seeds germinate at the same location, remove the weaker seedlings by snipping them at soil level with scissors. Do not pull them out, as this disturbs the roots of the remaining plant.

Tomato seeds being pressed carefully into prepared soil in a plastic grow bag
Pressing tomato seeds into moist soil at the correct depth before covering

Stage 2: Seedling Care

Once seeds have germinated and produced their first true leaves, they enter an active growth phase. During this stage:

  • Ensure consistent light — at least 6 hours of direct sun per day outdoors, or supplemental grow lights if indoors
  • Water whenever the top 2 cm of soil feels dry
  • Begin light liquid fertilisation once the plant has 3–4 true leaves
  • Protect from extreme temperature fluctuations

Stage 3: Transplanting Seedlings

Seedlings started in trays should be transplanted into their final grow bags once they are large enough to handle and the risk of frost has passed (for outdoor growing). Transplanting too early results in shock; transplanting too late can cause root-bound stress.

  1. 1

    Water Before Transplanting

    Water the seedling tray and the grow bag thoroughly one hour before transplanting. Moist soil reduces transplant shock and helps roots settle quickly.

  2. 2

    Make a Planting Hole

    Use a trowel to create a hole in the centre of the bag slightly larger than the seedling's root ball.

  3. 3

    Remove Seedling Carefully

    Gently tip the seedling from its cell, keeping as much soil around the roots as possible. Avoid pulling by the stem.

  4. 4

    Place and Backfill

    Set the seedling at the same depth it was growing in the tray (or slightly deeper for tomatoes, which root along buried stems). Backfill with surrounding soil and press gently.

  5. 5

    Water and Shade

    Water gently immediately after transplanting. If possible, place the bag in light shade for 2–3 days to help the plant adjust before returning it to full sun.

Stage 4: Active Growth and Pest Management

During active growth, plants require consistent watering, regular fertilisation, and monitoring for pests and diseases. For detailed watering guidance, see the Watering & Care page.

A fine mesh net placed over plastic bag plants to protect from insects
Fine mesh netting provides physical protection against insects without chemicals

Common Pest Management Methods

Pest Signs Method
Aphids Clusters of small insects on new growth; sticky honeydew Remove by hand or rinse with a stream of water; apply insecticidal soap if needed
Caterpillars Irregular holes in leaves; frass (droppings) on leaves Remove by hand; use fine mesh netting as a physical barrier
Slugs / Snails Silvery trails; irregular leaf damage Place bags on raised surfaces; use slug traps if necessary
Spider mites Fine webbing on undersides of leaves; pale stippled leaves Increase humidity; apply neem oil or insecticidal soap
Powdery mildew White powdery coating on leaf surfaces Improve airflow between bags; remove affected leaves; reduce overhead watering

Stage 5: Harvesting

Harvesting at the correct time preserves the flavour and encourages continued production in repeat-fruiting plants such as tomatoes, peppers, and cucumbers.

  • Leafy greens: Harvest outer leaves as needed; allow the plant to continue growing from the centre
  • Tomatoes: Harvest when fully coloured and slightly soft to the touch
  • Cucumbers: Harvest before they turn yellow; regular harvesting encourages more fruit
  • Peppers: Harvest green or allow to ripen to red/yellow/orange — both are edible at different stages
  • Radishes: Harvest promptly once mature; leaving them too long causes them to split or become woody
End of Season

After the final harvest, remove plant material from the bag and allow the soil to dry slightly. Store bags in a dry location or refresh the soil and replant with a suitable winter or spring crop. See the Soil & Nutrients page for guidance on refreshing soil between seasons.