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Horticulture 1000
HT1091 - Plant propogation 1 - Thinning seedlings
Sowing seeds in open ground Plant breeding

Thinning seedlings

Thinning out is reducing the number of seedlings in a crowded row. Plants grown from seeds sown directly in the ground are often overcrowded. To grow into useful sized plants, each plant needs room to spread its roots and leaves. If it doesn't have room there will be competition for light, water and nutrients. The plant will grow long and spindly and won't develop to its full potential.

When some crops are thinned, such as lettuce or cabbage, the seedlings can be transplanted elsewhere.

With most root crops, for example, radish, carrot, parsnip and beetroot, transplanting doesn't work very well. The thinnings are composted or eaten.

Before  thinning out seedlings, make sure the soil is moist. The seedlings to be  removed are easier to pull out and the remaining seedlings are less likely to  be damaged.

When thinning out seedlings, remove the weakest plants and leave the strongest ones.
    Work out the expected full size of the strongest plants and the space that they will need, and then pull out the seedlings growing in between.

A good time to thin out is when it's raining. If this isn't possible, thin out in the early evening after the heat of the day has passed and water each row immediately after thinning. Water helps to rinse the disturbed soil back round the roots of the remaining plants.

Carrot seedlings to be thinned Carrot seedlings to be thinned.
Radish seedlings to be thinned Radish seedlings to be thinned.

Key points   Key points

  • Thinning out is reducing seedlings in a crowded row.
  • Thinning out creates more space for seedlings to grow.
  • Thinning out reduces competition for light, water and nutrients.
  • When thinning, leave the strongest plants.
  • Watering after thinning helps rinse the disturbed soil back around the roots.

To complete the internally assessed  practical skills standard AS90157 you need to successfully complete three of the following practical tasks:

  • Sowing seeds in open ground HT1021Y1
  • Cuttings HT1022Y1
  • Collecting, cleaning and grading seeds HT1023Y1
  • Pruning HT1024Y1

What's next?

Go to: 7 Plant breeding.

Sowing seeds in open ground Plant breeding