Sowing temperatures

[Colin Miles]

First early potatoes generally don't store as well others and one of the reasons for this is presumably that they start growth at lower temperatures. Which set me thinking as to what is the 'best minimum' soil temperature in order to get them growing at a reasonable rate? Several years ago the ground was so wet that I wasn't able to plant them until May 7th but 7 weeks later they were cropping.

Similarly with Carrots, Parsnips, Peas, etc., there must be a 'minimum' temperature below which it is pointless to sow.

And can anyone recommend a good soil thermometer, or is it just a question of sticking anyone in the soil?

[Lyn]

I find it best to wait until the weeds start to grow in abundance - that gives me a very good indication that my soil is ready for seeds to germinate without them rotting off. Of course, if you use cloches or have warmed up the soil beforehand with polythene, you could sow a bit earlier - no doubt other people can give plenty of advice on this.
Regards, Lyn

[Chantal]

I'm sure someone on here said if you can sit on the soil with a bare bum then it's warm enough to plant.

However, I have NEVER tried this!

[andys]

Hi Colin,

I try to get my Maris Bard early potatoes planted at the beginning of Feb and cover them with a sheet of clear polythene as long as the ground is not frozen or waterlogged and is not shaded. The polysheet should stay over the foliage until the last frosts have passed or the plants growth will be checked if frost damage occurs.
I was eating good quality new potatoes by late May last year even though we had a cold Feb & March.

I wouldnt sow peas or carrots in soil with a temperature below 7 degrees Celcius as a large percentage of the seeds will rot - however parsnips will germinate in temperatures below 5 degrees C although very slowly.

Lynns idea of watching for weed germination is good benchmark for sowing peas outside - I find that stinging nettle seedlings seem to start to germinate at 7-10 degrees C which is OK for germinating Peas & Carrots whilst chickweed tends to germinate at around 4 degrees C so could be used as a marker for early sowings of parsnips

You could always start some peas off indoors in Feb sown in compost in seed trays or root trainers and transplant outside in March but keep them in good light and keep the temperature down to around 10 C
or the peas will become etoliated (spindly) and the stems may snap

Good luck,

Andy S

[John]

There might be a bit of confusion here between true seeds and 'seed' potatoes. There are wide differences between vegetables in temperatures at which their seeds will germinate well. Carrots, parsnips and beetroot germinate well at high temperatures but poorly below about 7°C. At low temperatures germination is slow, taking several weeks during which the seed is vulnerable. Peas will germinate successfully from temperatures as low as 5°C up to 32°C.
'Seed' potatoes of course are not seeds at all but small tubers, underground stems that have the ability to develop into new plants. If you put them into the soil they will start into growth whatever the temperature, providing it's not freezing. Some varieties have a resting period or dormancy before growth will restart- this is weak in earlies. The higher the temperature the faster the growth - in fact as a general rule for each 10°C increase in temperature the growth rate will double. The problem with potatoes, as far as early planting goes, is that their foliage requires frost protection. I was clearing some ground today and found some of last year's crop with well established roots and shoots.

John

[andys]

Colin,

Try this factsheet on the net

cesonoma.ucdavis.edu/gardener/pdf/soil_temp_vegetable_seed.pdf

It has max/min and optimum germination soil temperatures

Andy