Page 17 - Simply Vegetables Spring 2023

Sowing and planting times for the UK
In the survey carried out by Raymond Higgins in 2020 one of the requests
was for an article on the different sowing times between the North and South of the U.K. I suspect the request was from one of our Northern or Scottish branch members as it must be frustrating that most books, articles, and T.V programmes tend to focus on the southern U.K with the exception of Beech Grove in Scotland. I wish it were as simple as saying sow / plant two weeks later but it’s not and I will explain why but hopefully give you some advice.
There are several factors that affect when it is right to sow or plant these include the crop as some are hardier than others, the microclimate in your garden / allotment, the latitude and altitude of the plot, is the area prone to cold winds or a frost pocket and how close to the sea is the garden.
The main limiting factor of when to start sowing / planting is the soil temperature, although air temperature is a big factor if planting as cold and frosts can damage the foliage. Most hardy vegetables will
not germinate well until the soil is 5°C or higher and some will require 7°C to get reasonable germination. A
simple soil thermometer
is all that is required to
make the decision on
when to sow, these are
not expensive and is
better than any advice
in books, magazines,
internet, or TV / radio.
You just need to know
the required germination
temperature for the crop
being sown, then check
the soil temperature for
three to five days and see
if it has settled at the required
temperature, if so, start sowing. Do
not use the air temperature as the soil temperature lags behind this by a good way, it is the soil temperature that is critical, and it does not fluctuate as much as the air temperature only moving slowly both up and down. As the air temperature increases the soil temperature slowly rises but very slowly and it is this temperature that is the critical one for seed germination and root growth. There is no point in sowing seed into a cold soil it will not germinate until it has warmed up and is likely to rot.
What tends to dictate when to start planting is when the last frost or at least severe frost has gone, although frosts tend to lower the soil temperature it is the damage caused to some plants that tends to be the problem. If planting hardy vegetables like Brassicas, modules of beetroot, onions, chard, lettuce, etc. these
will withstand light frosts if hardened off properly whereas runner or French beans would be damaged by the frost.
Looking at some of the other factors that affect the sowing /planting dates starting with latitude, i.e., how far north is the garden, the further north the later the spring and usually the colder the winter so the later the soil temperature in warming up. This also affects how early the autumn comes and growth slows down or stops.
The date of the last frosts and when spring starts tends to move up the country from the southwest up to the northeast (see diagram) and is also affected by the altitude so looking at Yorkshire (Gods own county as any Yorkshireman will tell you!) spring arrives earlier in east Yorkshire
produce better crops. South or southwest aspects are good, north and northeast not so good. In the northern parts of the U.K a south facing slope can make a big difference allowing early sowing and even the ability to grow crops not considered hardy in that area.
Moving on to the area, this can be a major factor especially if you live within five to ten miles of the sea, many early crops are grown in Cornwall and South Wales along the coastline as they have very few frosts and have the full effects of the gulf stream. The west coast of Scotland is famous for the range of less hardy plants that can be grown there even overwinter compared to much further south. A southwest facing slope on the west coast will produce crops way earlier than the east side of Scotland.
There are other areas of the country that have “local climates” which will affect how early you can sow; the north end of Norfolk is known for the cold easterly winds it tends to suffer in the spring that will delay sowing. Check the local climate where you live as this will give a guide to how soil temperature will vary and move as well as dates for the last frosts.
Living in a frost pocket will make a big difference as the frosts are likely to last longer and be more severe which will delay the soil warming up and affect plant growth if the plant is not fully hardy. Think back to Adrian Baggaley’s article in the October
2022 Simply Vegetables on protecting the flowers on his fruit trees!
Soil temperature is also affected by the type of soil, a heavy clay soil is a lot slower to warm up than a free draining sand for the simple reason clay holds more water which needs to be warmed up before the
soil will warm up. If on a clay soil try to improve the drainage or consider raised beds, add
as much organic matter as possible and any coarse sand or grit if available.
If you just want a guide as to when to sow / plant the diagram will give rough although vague idea, if you want more accurate detail buy a soil thermometer, they are not very expensive and are useful for both soil temperature and compost heap temperature. If you are too mean to buy
the thermometer, I am told in the good old day’s farmers would prepare their ground for sowing, get out of the tractor, take their trousers and underpants down and sit on the soil, if it felt cold it was too cold to sow! Be careful doing this on the allotment!
Kelvin Mason
compared to living on the Pennines which is at a higher altitude. This is also true of the higher altitude areas in Scotland.
The predominant direction of the wind in the U.K. is from the southwest and this tends to be mainly warm air from the gulf stream which is why the spring arrives first in the southwest and along the western side of the country, although it is often wetter!
The next factor to consider is the aspect of the garden / plot (the direction it
faces) a southerly facing slope will be far earlier than a northerly one and is likely to
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