When is it safe to plant tender plants in 4-seasons-in-a-day Scotland?

The Herald Scotland

10-05-2025

Based on averages from previous years' data collected by the Met Office, the last light frost date in Aberdeen is April 13, East Lothian April 26, East Renfrewshire May 3, and in the southern Borders, I'm not in the clear till May 24.
It's hard to be patient when you see buds starting to open and you hear the buzz of insects, but even they can get it wrong.
We should remember these are only average frost dates, so the safest approach is to leave outdoor planting for 10-14 days after the average for your area.
But how many of us can be as patient as that? I certainly can't, especially as there are ways of usually getting away with it.
Hardening off young plants in advance certainly helps. This entails spending a week lugging them in and out of a cosseted greenhouse.
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But since overnight temperatures can be pretty low in a cold greenhouse anyway, the transition may not be that much of a shock and won't protect against an unexpectedly late frost.
For tender plants to steadily grow well, night-time temperatures shouldn't fall below 8C with 15C during the day.
And if the mercury falls low enough to seriously damage the likes of tomatoes, leading to scorched leaves or desultory growth, you may need to chuck the plants and buy from a garden centre.
With fast growers such as courgettes or runners, sow again - they'll soon catch up.
Undoubtedly the best protection when a cold night is forecast is to cover plants with fleece.
I even have a little frame for celeriac to lend a helping hand.
If the roots are to swell enough, they must be planted out before the end of May, when reliably warm weather can't yet be guaranteed.
When using fleece this way for a couple of weeks, I raise it above the plants to allow for good air circulation and keep damaging frost away from the leaves.
But you can simply throw the fleece over a crop if it's an emergency one-nighter.
The frost will only last an hour or two when the nights are short.
Finally, be canny with watering.
Small plants don't need much and you don't want the little roots to be damaged when the surface soil is both wet and cold.
Water early in the day at this stage, leaving evening watering till plants become larger.
Plant of the week
Syringa 'Pink Perfume' (Image: Supplied) Syringa 'Pink Perfume' is a small lilac, growing slowly to about two metres, with sweetly scented blooms in a pretty shade of pink.
The main flush of blossom is this month but it continues to flower intermittently throughout the summer.
It can be grown in a large pot but will probably thrive better in reasonably drained soil in a sunny position where the warmth will bring out the scent.