Growing and Planting Seedlings

When growing seedlings, it's important to manage light intake and be careful to not overwater. If grown indoors, they should be gradually acclimatized to conditions outdoors before planting.
Plug Plants in Plastic Containers

Plug Plants in Plastic Containers

Plug plants are plants ready for actual planting. They are designed to be introduced to a garden or landscape with substantial growth already established. They can begin to produce flowers, fruit or vegetables much sooner than traditional seed planting.

Photo by: DK - The Complete Gardener's Guide © 2011 Dorling Kindersley Limited

DK - The Complete Gardener's Guide , 2011 Dorling Kindersley Limited

Plug plants are plants ready for actual planting. They are designed to be introduced to a garden or landscape with substantial growth already established. They can begin to produce flowers, fruit or vegetables much sooner than traditional seed planting.

The time it takes for seeds to germinate and produce a visible shoot above the soil varies greatly, ranging from a day for plants like cress and radishes, to a year or more for some shrubs and trees. Note that the first pair of leaves to develop may look different from those that follow. They are called the “seed leaves.” 

If you are germinating seeds in darkness, check them regularly and move into good light once the seedlings emerge to encourage sturdy and healthy growth. They will grow tall, thin, and pale if left in the dark, but keep them out of bright, direct sunlight, which can scorch tender leaves. Keep seedlings warm, although they usually tolerate lower temperatures than those for germination. 

Do not let the seedlings dry out at any stage, but avoid overwatering, which can drown the roots. Use a copper fungicide to reduce the risk of damping-off disease. Water small seedlings from below as for seeds, but more robust kinds, such as lupines and peonies, can be watered gently from above. Use a watering can with a very fine spray, and start and finish with the can to one side of the container to avoid letting heavy drips fall on the plants. Allow containers to drain thoroughly after watering, and never keep them permanently in trays or saucers of water. 


  • Use plug plants if you don’t have time to raise plants from seed. Water them when they arrive, and use the blunt end of a pencil to push the plug plants out of their modules.
  • Grow plug plants on in module trays filled with potting mix, making holes in the soil using a dibber or pencil; keep the plants in a light, airy place. Water from below by placing the module in a tray of water.

Getting Ready for the Garden 

When you have pricked out your seedlings, grow them at the temperature recommended on the seed packet. Check them daily and water whenever they look dry. Plants in trays can usually remain there until they are planted out, but some vigorous seedlings in pots may need to be moved again into containers 1–2 inches wider than their root systems. If planting out is delayed and the foliage starts to turn yellow, fertilize with a balanced liquid fertilizer. 

Plants that have been raised indoors make soft growth that is vulnerable to wind and cold. They must gradually be acclimatized to conditions outdoors—this is known as “hardening off.” Several weeks before planting out, place plants in a cool spot indoors. A week or so later, stand them outside for a few hours each day somewhere that is both sheltered and shady, covered with a double layer of horticultural fleece. It is important to bring them in at night. Leave them out for a little longer each day and then remove one layer of fleece. About a week before you plant them out, remove the fleece during the day, but leave them out at night still covered by the fleece. 

If you have an unheated cold frame, place the containers of plants in this instead of using fleece, keeping the lid shut for a few days. Gradually increase the ventilation, opening the lid just a crack to start with but eventually leaving it fully open, at first during the day and then at night too. 

Planting Out 

Plant out as soon as the young plants are hardened off and the weather is suitable: mild, damp conditions are best. Wait until all threat of frost is past before risking half-hardy plants outdoors. Prepare the site thoroughly in advance, and water the plants well and leave to drain before planting. 

Tap each side of a tray sharply on the ground to loosen the soil, then slide it out in one block and separate the plants carefully with your fingers or a trowel. Release plants from modules by pushing on the base of the cells; some modules are torn apart. Check the seed packet for planting distances. Make a small hole for each plant, carefully place it in position, draw the soil over the roots, gently firm it down by hand, and water it in.

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