Just because warmer April days have arrived, be warned.
Overnight temperatures in April have been exceptionally cold, more than often dropping below freezing, giving morning frosts &, it’s been exceptionally dry too - there’s been virtually no useful rain.
The forecast for the remaining few weeks of April 2021 is to remain unusually dry & for the return of artic winds on Wednesday 21st April
These two charts show the actual rainfall & overnight temperatures this month from a private garden which backs onto the allotments.
WHAT DOES THIS MEAN FOR PLOT HOLDERS ?
Below is a guide to help you to keep your plants & seedlings alive, improve their vigour during this year’s unusual April weather &, ultimately help maximise your harvest this summer
GREENHOUSE TEMPERATURES
Without intervention temperatures in April will be fluctuating between approx -1/-4°C overnight to + 40/45 °C during the day.
For young plants / seedlings this will feel like summer in the day & winter overnight & they will either suffer or just give up the ghost completely.
Left - Greenhouse thermometer readings show a temperature of -2.5 °C overnight on Sunday 11th & already by 9.29am on Monday 12th April it was 43.3 °C .
Right - Tomato plant suffering from temperature extremes - too hot by day, too cold by night
Ideally greenhouse temperatures should be kept as steady as possible but try to keep above 12 °C over night & below 30 °C in the day.
OVERNIGHT - above 12 °C
In unheated greenhouse you can protect tender plants such as Tomatoes, Melons, Courgettes, Flowers etc by either wrapping them in fleece &/or raise the temperature up by burning a candle or tea light under a crockery pot. As a rule of thumb just make sure it doesn’t drop below 5 °C
Left - Raising overnight greenhouse temperatures using a lite candle under a crockery pot. Obviously, don’t use a plastic pot - it will melt.
Right - Wrap tender plants overnight with fleece
DAYTIME - below 30 °C
Open the greenhouse door / window during the warm sunny days or use shade. Hardy plants & seedlings such as brassicas and peas should survive the colder nights without any additional protection but will not thrive in excessively high daytime temperatures created when greenhouse doors / windows are kept shut.
Seed germination requirements vary too much to give general advice. Follow the recommended instructions on the packet.
OUTSIDE
The cold nights will be keeping soil temperatures down & combined with the lower rainfall levels the following intervention is advised.
1. SEED GERMINATION - parsnip, beetroot, carrot etc
Early sowings of seeds will be struggling to germinate in the current cold & dry conditions. Keep sown seeds lightly watered & consider covering with fleece or cloches if you want to improve germination rates.
Don’t be surprised if early sowings need to be repeated because of seed germination failure.
2. OVERWINTERED ANNUALS - onion, garlic, broad bean etc
Although hardy enough to withstand the colder nights, without enough rainfall our overwintered crops such as onions, garlic & broad beans etc will not be able to put on the growth spurt we expect now warmer April days have arrived.
A throughly soaking once a week will encourage deeper rooting & is always much better than a daily sprinkle of surface water, which will only encourages shallow rooting.
3. EARLY SPRING ANNUALS - broad bean & pea & potato etc
Again, although hardy enough to survive the outside cold nights & morning frosts, early spring planting outside of broad beans & peas etc, grown on in the greenhouse, should be hardened off in a cold frame before planting out. Again, keep watering as this dry spell continues.
Seed potatoes will benefit from being planted in a pre - watered trench before being covered with soil.
4. LATE SPRING ANNUALS - runner bean, sweet corn, courgette etc
Heed the May frost warning below. Keep emerging potato plants covered with soil & hold back on planting out all greenhouse grown tender plants until after the last May frost & always harden off first.
5. NEWLY PLANTED PERMANENTS
For newly planted fruit, asparagus etc, again encourage deep rooting by thoroughly soaking once a week.
6. ESTABLISHED PERMANENTS - EG:- rhubarb, asparagus & fruit etc
Most will have enough deep root structure to find the available water deeper down in the soil & will not need assistance during this dry April.
Hopefully the blossom on early flowering fruit will have successfully set despite the cold nights & frosty mornings - time will tell.
STRAWBERRY - Evolved from an alpine species, strawberry leaves are relatively hardy & able to withstand low temperatures, but their spring flowers will suffer from frost, turning the centre back.
Fleecing, although not full proof, will help prevent the flower damage. With relatively shallow roots & trying to flower right now, strawberries are probably the only fruit to consider watering now during this April’s drought. Again, a once a week thoroughly soak is better than a light daily sprinkle.
WARNING - EXPECT FROST IN MAY
Plot holders diaries show it’s almost certain we will have at least one frost event in May.
However, last year nearly everyone was caught off guard by a late hard frost for three consecutive mornings during the second week of May !!
This three day killer in 2020 finished of many tender plants in the greenhouses as temperatures suddenly plummeted. It severely damaged emerging potato plants & the runner beans. It also totally destroyed most of the ‘set’ soft fruit & late flowering tree blossom on the site. Most plot holders either lost their fruit harvest altogether or had a very much reduced yield
Always keep an ear open for frost warnings during May and take appropriate action -
Heap soil to cover emerging potato plants, although frost damaged potato plants will recover.
Fleece tender plants both in the greenhouse & outside.
Whilst fleecing to protect tree blossom is an enormous task , if possible, fleece fruit bushes with ‘ just set fruit’ or that are still in bloom.
A Gardeners Diary - Published in 1938
The Days of the Three Icemen
12th, 13th, 14th May
Below is a Facebook post from Plot Holder Wendy Necar following last years disastrous May frost event
