Hardening off – essential for your seedlings

Yesterday I was giving a demo on seed sowing at Springmount garden centre (there is another on Sat April 12) and although it was simple enough to demonstrate sowing seeds and transplanting seedlings – in fact everyone got to have a go – the aftercare is not quite as simple. Everyone has different conditions and sometimes it can be a challenge to grow seedlings on the windowsill. A greenhouse makes it all much easier. But one of the most difficult aspects to get across is ‘hardening off’.

To glibly say that it is getting the plants used to outside conditions is too simple. How do you do this?

In a perfect world you grow the seedlings in a greenhouse and then move them to a coldframe (which, as its name suggests is unheated) for a few weeks before the small plants have to face the outside world alone.

But why do it? I always think the best analogy is if we are covered in clothes for 50 weeks of the year and then go on holiday and lay on the beach all day on the first day – we get sunburn. Your seeldings have been protected from wind and rain and full sun all their lives. If you plant them straight out in the garden they get a total shock and if they don’t die they get scorched and are set back.

To start the hardening off process, bearing in mind that in most places in the UK and Ireland yo cannot plant out frost-tender plants till late May, put the plants outside on a dull, mild day (read ‘a soft day’ if you are Irish) and bring them back in at night. Repeat this for several days so they toughen up a bit. But do not leave them out on frosty nights unless they will tolerate frost – like these brassicas and parsley plants below.

Before you plant out tender seedlings they must be 'hardened off'

Before you plant out tender seedlings they must be ‘hardened off’

Most plants do not need hardening off until late April but unless you have unlimited space in the greenhouse you will have to start moving plants out after a while. I will put the antirrhinums out next to make more room – they will tolerate cool conditions.

To book on the course (10 euro) visit http://www.springmount.ie


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