Page 31 - Simply Vegetables Spring 2021

corn or runner bean which originates from the warmer climes of South America. This is why lettuce can be sown outdoors in March and runner beans not until May when the soil has warmed up.
Seeds will germinate within a temperature range, for example lettuce the range is 5 to 23°C, but other vegetables have a smaller range. The lower part of the range is likely to result in slower and lower germination with the mid to upper range giving the best germination. The highest level of the range is likely to be slightly lower germination. Too high a temperature will inhibit germination as it can result in the enzymes in the seed closing down.
If sowing indoors set your propagator to the temperature recommended on the seed packets which is likely to be in the range of 15 to 23°C for most vegetables and 23 to 27°C for cucumbers and pumpkins etc. if you do not have an electric propagator (they are well worth having) then ensure that the air temperature is within the range required. Airing cupboards are useful to start seeds but check them at least daily or they may dry out or germinate and be drawn up and yellow!
Outdoors we do not have the ability to control the temperatures (let me know if you can!) so we are in the hands of the weather. Before doing any sowing you need to know the temperature of the soil, this is easily done using a soil thermometer (which are a reasonable price from garden centres and horticultural suppliers) and they are useful to check the temperature of the compost heap. Push the thermometer approx... 50mm (2”) into the soil, not any deeper as the soil will be colder the deeper you go. In the spring soils warm from the top down and the seed will be sown in the top 10mm for many seeds, 20mm for larger seeds and 50mm for beans and peas. Check the soil temperature (not the air temperature as this will be higher) over a period of a few days to ensure it is reasonable consistent; it needs to be in
the correct range for 5 to 6 days to ensure
it will stay within the range while the seed germinates.
There are methods of speeding up outdoor seed germination and these
include covering the soil with black or
clear polythene, cloches (glass, plastic or polythene), fleece, weed mulch or Mypex (or similar material). Put this in place 10 to15 days before you wish to sow.
Soaking seeds will also give a quicker germination, many people have soaked their peas and beans overnight before sowing over the years, but many other seeds can be soaked before sowing. Once soaked they must be sown or kept damp, if they dry out the seed is likely to die. Soaking in a very dilute seaweed feed solution is reputed to improve germination.
Fluid drilling is a technique that became popular in the 1970’s following work at the National Vegetable Research Station but it has never really taken off either with amateur or commercial growers; possible as it involves a bit of extra work. It is very useful for parsnips that can be difficult to germinate. The method is simple line a
sandwich box with a layer of 5 or 6 paper towels and wet these, drain off any surplus water. Sow the seeds on the towels and cover with some more wet paper towels. Put the lid on the sandwich box and place it in a warm area (propagator or airing cupboard). Check the seeds daily and as soon as the radicle (root) start to come out of the seed coat move to a slightly cooler environment. They can held in a fridge for a few days but not too long, don’t let the radicle get more than 2 to 3mm long otherwise it will be damaged when sowing them. When ready to sow prepare the ground and drill as for normal sowing, then carefully wash / brush the germinated seeds into a jug or similar container containing ready mixed wallpaper paste. Mix the seed into the paste carefully and then pour it into a polythene freezer bag and cut one of the bottom corners off. The seed can now be sown using a method like icing a cake by squeezing the mixture along the drill and then covering it with soil.
Other techniques for improving germination include the using of primed seed which can be brought from some
seed suppliers. Primed seed is soaked in
a solution (usually of polyethylene glycol) and then dried, doing this speeds up and improves the germination percentage. In
the future it may be possible to buy seed that has been treated with Gibberellic acid which is a growth regulator that can improve germination. Also there is a fungus called
Seed Germination Temperatures
Trichoderma harzianum that is thought to help in germination.
A couple of other techniques that are worth a try is to cover rows of parsnip seed with a plank after sowing, this keeps the seed moist and improves the germination level; it works! With indoor sowing keep the growing media consistently moist but not too wet and use tap water not water butt water which can carry water borne diseases. Avoid using water that has been treated by a water softener as it may contain salts which can inhibit germination. Clean all seed trays and pots in hot water which is 10% bleach, so 9 parts water to 1 part bleach. A slightly more unusual method is to use vermicompost (worm castings) to cover your seed whether sowing indoors or outdoors. When covering the seed mix in 5 to 10% worm castings
by volume into the soil or growing media, apparently worm casting contain some Gibberellic acid that helps with germination. As an alternative a worm casting tea can be made and used to water the media.
Finally if you sow some seeds and the germination is poor or non-existent ask
a few questions and think things through before blaming the seed companies. It is rare for “faulty” seed these days (although not unknown) and more likely the poor germination is owing to old seed, poorly stored seed, too cold, sowing too deep, pests or diseases; in the summer it could be too hot or dry. Happy Sowing!
Vegetable Crop
Minimum temperature °C
Best Range °C
Aubergine
French & Runner Beans 8 Cabbage & other Brassicas 5 Cauliflower / Calabrese 5 Celery 5 Leek 5 Onion 2 Parsnip 2
16
- 10
24 - 30 16 - 25 7 – 25 7 – 25 15 – 21 18 - 25 10 - 25 10 – 21 18 – 30 7 – 25 21 – 30 16 - 30
15 - 23
Broad Bean
7
15 - 20
Beetroot, chard
5
10 – 25
Carrot
5
7 - 25
Celeriac
10
20 - 25
Cucumber
16
18 – 30
Lettuce
2
5 – 23
Parsley
5
10 – 25
Pea
5
5 – 23
Pepper Radish Squash Sweet corn Turnip
16 5 16 10 6
Pumpkin
16
21 - 30
Spinach
2
7 – 23
Swede
6
15 - 23
Tomato
10
16 - -30
Simply Vegetables 31