, written by Benedict Vanheems 
There are a few tricks you need to know to help your seedlings develop into sturdy plants and safely make the transition to growing outside. Let's get started!
Pricking Out Your Seedlings
‘Pricking out’ means separating out seedlings growing together and transferring them into their own plugs or pots of potting mix. Start pricking out as soon as the seedlings are big enough to handle.
Fill plug trays or pots with good quality all-purpose potting mix. Carefully ease the seedlings out of the tray they were growing in then gently tease them apart. Try to retain as much of the original potting mix around the roots as you can. Work with small batches of seedlings so they don’t dry out while their roots are bare.
Make holes in the potting mix with your finger, a pencil or something similar. Lift each seedling carefully, only ever handling them by their leaves, never the delicate stems. Carefully feed the roots right down into the hole then gently firm the seedling in. You can bury some of the stem if the seedlings are looking a little leggy and drawn. This will help to support them.
Once you’re done, water the seedlings with a watering can or hose fitted with a fine rose. Don’t worry too much if the seedlings get a little flattened, they’ll soon recover.
Choosing Seedling Containers: Plugs vs Pots
Trays with smaller plugs suit most salad crops, especially if they will be transplanted promptly within three or four weeks of sowing. Larger plugs suit bigger, hungrier seedlings such as those of the brassica cabbage family. They’re also great for other vegetables that benefit from growing on a little before planting, such as onions.
Larger seedlings, or those of tender crops like tomato or pepper that won’t be planted out until after the last frost, are best pricked out into individual pots. They grow fast and may need to be potted on once again before they are transplanted into their final growing positions.
Preparing Seedlings for Planting
Water seedlings to keep the potting mix moist, but be careful not to overwater. If you’re growing in a greenhouse, tunnel or cold frame, ventilate it on mild, sunny days. This will help keep the air inside moving, and reduce the risk of disease and moulds.
Cool-season crops like lettuce, onions, beets or peas can go straight outside as soon as the ground is ready, meaning that the soil is no longer cold and wet, and has reached around 50ºF (10ºC). You can help encourage stronger seedlings in preparation for the move by occasionally running your hand gently over the seedlings.
Plant seedlings out while they are still quite young if outdoor conditions allow - sometimes as soon as three to four weeks after sowing. Our Garden Planner can help you work out when is the best time to transplant outdoors. Check out the green bars in your Plant List for a range of recommended dates for your location.
Younger seedlings tend to establish quicker than those that have become root bound in their containers. Getting them outside while they’re young will also free up valuable space under cover. Nevertheless, hold back a few spares under cover if you can – just in case.
Hardening Off Plants
Tender plants need acclimatizing before planting out – a process called ‘hardening off’. Position plants in a sheltered spot outside during the day for a short time. Gradually extend the amount of time that plants are outside over the course of a week or two, until they’re staying out all day.
If you’re not able to be around to bring your seedlings back in during the day, another option is to place your seedlings into a cold frame and gradually increase the amount of ventilation by opening vents progressively wider each day. Make sure to shut them down completely before dark.
How to Transplant Seedlings
Plant seedlings into prepared soil – that’s soil that has been enriched with well-rotted organic matter such as compost. Remove the seedlings from their plug trays or pots then lay them out onto the surface, ready to plant. You can use a tape measure or ruler to get the spacing right, but with practice you’ll be able to space them out by eye.
Use a hand trowel, a dibber – or just your fingers – to make holes in the soil. Drop each seedling into its hole then firm in around the rootball. Lankier seedlings can be planted deeper, so long as you don’t bury the lowest leaves. Water the newly planted area to settle the soil around the roots.
It’s important that the rootballs are moist before planting. If they aren’t, stand plugs in a bucket of water until they’re soaked through.
Protecting New Transplants
At the start of the growing season new transplants can be helped along simply by covering them with row cover or horticultural fleece. This traps a little of the sun’s warmth and helps to shield seedlings from low temperatures and drying winds. It also protects them from birds who love tender shoots. Secure the covers in place so they’re snug against the plants and not flapping about. Weigh down the edges to prevent the wind sneaking under the sides and lifting the cover off. Remove covers once the weather has warmed up a little more. You may need to put down beer traps to avoid problems with slugs and snails munching your seedlings.
Once your seedlings are planted out you really begin to get a sense of the bounty to come. How do you help your seedlings make the transition from indoors to out? You can share all your tips and suggestions in the comments section below.
< All Guides
