Friday, 24 February 2017

Soil Temperature and Seed Germination

A few days ago we sowed the tomato seeds for this season's market and home garden. It never ceases to amaze me what little indoor space you need to rear thousands of seedlings. We use two 50 cm x 30 cm x 15 cm trays to germinate approx 150 seedlings from 10 cultivars. When they get bigger we move them into two 1.3 x 8 m beds covered with polythene to rear them before they take their permanent positions in the gardens in early - mid April.



Many of the plants we grow I prefer to sow directly outside and one of the most important things to consider when sowing is that the temperature of the soil is high enough for the seed to germinate.

Other important considerations include:
  • whether the seed requires any pre-treatment before it will germinate, i.e stratification and scarification (mainly relevant for perennial plants particularly trees and shrubs).
  • how deep you sow the seed - too shallow is better than too deep. 
  • that the correct moisture levels are kept constant during the germination phase - not too wet, not too dry and with the ideal moisture levels similar to that of a wrung out cloth.

Elaeagnus commutata -  Epigeal germination 

This post we'll focus on soil temperature for germinating seeds. We'll look at why this is important, how to take soil temperature, and I've included a table showing the minimum and preferred soil temperatures for germination of some common plants.

Eruca sativa - Rocket germinating 

Often you will find a monthly guide on a seed pack indicating when to sow seeds and this generally works okay, but can be misleading. If you have a long cold winter and the soil is cold, germination will be delayed and in some cases the seeds may rot in the ground.  On the other hand, if the soil is unusually warm in the spring, it's possible to seed earlier. Being able to tell the soil temperature and being aware of the preferences of each plant will result in more or your seeds germinating.


Tomato seedlings

Measuring Soil Temperature


You want to measure the temperature at seeding depth and this will differ for each seed you sow. The general rule is sow to a depth of no more than twice the diameter of the seed, but like I said above it's better to go too shallow than too deep.

Any thermometer that will measure temperature at a specific depth can be used to measure soil temperature. Insert the thermometer into the area where the seeds will be sown and wait a few minutes before you take a reading.

Bear in mind that each area of your garden will probably have a different temperature. The soil temperature is influenced by the following factors:
  • Bare soil warms much faster than mulched soil and vegetated soil.
  • Dry soil will be warmer than wet soils.
  • South facing soils will be warmer than north facing, and the amount of shade cast on the soil will affect the temperature considerably. 

Gingko biloba seedling 

Warming up the Soil


As the air temperature starts to warm up in early spring you may like to get a head start with your sowing and accelerate the warming of the soil. If you have a mulch on your soil for the winter you can temporarily remove the mulch. The dark coloured soil will absorb all wavelengths of light and convert them into heat, warming the soil much faster. Another alternative is to leave the mulch on and cover the bed with a plastic sheet or glass pane. On a sunny day this will provide considerable heat. Of course you can also remove the mulch and use the sheet or glass on the bare soil and this has the added benefit of germinating any seeds in the patch that can be pulled before you start sowing.


Here's a table providing the minimum and preferred soil temperature for a number of crop seeds and the estimated time it takes the seeds to germinate


 Minimum and Preferred Temperatures for Common Crops







Basil Seedlings


Regenerative Landscape Design - Online Interactive Course 


If you would like to learn how to design, build and manage regenerative landscapes we'll be running our second Regenerative Landscape Design - Online Interactive Course that starts on May 1st, 2021. 

We're super excited about running the course and look forward to providing you with the confidence, inspiration, and opportunity to design, build and manage regenerative landscapes, gardens, and farms that produce food and other resources for humans while enhancing biodiversity.

Regenerative Landscape Design Online Course

You can find out all about the course here and right now we have a 20% discount on the full enrollment fees. Just use the promo code SUB2021 in the section of the registration form to receive your discount. The offer is valid until the 15th of March 2021.

We are looking forward to providing you with this unique online learning experience - as far as we know the very first of its kind, and if you are thinking of reasons why you should do this course and whether this course is suitable for you, take a look here where we lay it all out. Looking forward to it!

--------------------------------------------------------------------------------------------------------------------------

We offer a diversity of plants and seeds for permaculture, forest gardens and regenerative landscapes including a range of fruit and nut cultivars. We Deliver all over Europe from Nov - March. - Give a happy plant a happy home :)


Our Bio-Nursery - Permaculture/Polyculture/ Regenerative Landscape Plants 


--------------------------------------------------------------------------------------------------------------------------

Design and Create Webinars - Forest Gardens, Urban Gardens, Permaculture, Regenerative Farming   


We're hosting a range of online learning sessions including how to create habitat to enhance biodiversity, how to design and build a forest garden, polyculture design software tutorials, regenerative farm, and landscape design, urban gardening and much more. If you would like to be notified when our next sessions are coming up please add your email below and hit subscribe and we'll be in touch.




You can also register for our online training, services, and products directly here.


--------------------------------------------------------------------------------------------------------------------------

Support Our Project 




If you appreciate the work we are doing you can show your support in several ways.

  • Donate directly to our project via PayPal to balkanecologyproject@gmail.com or via Cash App to £Sytoma 
  • Comment, like, and share our content on social media.

--------------------------------------------------------------------------------------------------------------------------

References 

http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex1203
http://www.rodalesorganiclife.com/garden/plant-seeds-right-depth



3 comments:

  1. Good. Any study on growing trees in changing temp, air and soil.

    ReplyDelete
  2. This comment has been removed by a blog administrator.

    ReplyDelete