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Growing Tutorials

Sowing seed in modular trays

My vegetable growing career took a serious shot in the arm when Niall and myself started Quickcrop. This was mainly due to our association with two of the best growers in the country, Dermot Carey and Klaus Laitenberger. I moved very quickly from pottering about the garden to having some serious firepower looking over my shoulder.

Like most professional growers Dermot and Klaus start a lot of their plants off in modular trays. There are many good reasons to do this, I’ve listed the main ones below.

 

  • You can start plants out earlier by sowing indoors.
  • The plants suffer very little root disturbance unlike more traditional methods of pricking out seedlings from seed trays.
  • Quick transplanting. The seedling comes easily out of the tray in a small compost plug which is very handy to plant.
  • Uniform plant development as each seed grows in its own compost plug.

Convinced? O.K. here’s how its done:

We use 84 cell seedling trays which give a seedling plug of about 2 inches in depth. Clearly you won’t need 84 of each plant so plant rows of as many as you need. Make sure to mark the rows with the seed variety and the date you sowed them. They look great when you have a full tray containing rows of different plants, this is how our customers get them when we send out our seedling plant trays.

Use a fine seed compost for sowing. Seed compost is a finer grade and also lower in nutrients than multi purpose compost. This is important as too high nutrient levels will literally fry the tiny roots of the new seedlings.
Fill the seed tray with compost and brush off any excess. When filling the tray rub the compost through your hands to break up any lumps. Give the tray a sharp bang on your table to settle.

With your fingers make small depressions in each cell about a fingernail or 1.5cm deep. This is an average and some seeds may require a deeper or more shallow hole.

 

 

Sowing seeds in modular traySowing the required amount of seeds per cell can be tricky so here’s a good tip Klaus showed me. Fold a piece of paper to create a tight gutter which makes the seeds line up in a nice neat row. Use a pencil to push each one over the edge as you go along, it really makes it so much easier.
A pencil is much better than a biro as the seeds sometimes stick to the ink on the end of the pen.

Cover the seeds with another layer of compost then scrape across the top of the tray with a stick to remove excess. Don’t compact the compost with your hand, leave it nice and loose making it easy for the seedling to push through.

 

 

Gently water your seeds. A good tip is to use a plastic bottle with small holes punched in the cap. This is less likely to wash the seed around than the heavy spray from a watering can. Be careful with watering as you can do much more damage with too much water than too little in the earlier stages. The compost needs to be moist for germination but not soaking. Don’t forget we have no roots yet to soak up water so the seed can rot in the compost if left too wet.

You can watch the process at the start of each of our videos, here’s our beetroot one:

Place your trays in your greenhouse, polytunnel, cold frame or windowsill to germinate. Most seeds will germinate in a couple of days and be ready to plant out in about 4 weeks.

If you’re starting off seedlings early in the year on a heat bench or a windowsill you need to be careful they don’t get long and spindly or ‘leggy’. It’s quite simple really:

  • Most seeds need heat and moisture to germinate. They don’t need any light, this is why you can germinate seeds in an airing cupboard. (Lettuce and celery are exceptions here, they do need light)
  • Once the plant has broken the surface of the soil they need heat, moisture and light. If you have heat but no enough light the seedling will grow tall and thin searching out more sunlight. This creates a weak plant that is unlikely to thrive.
  • If you have plenty of light but not enough heat the plants may fail to germinate or grow very slowly.

As a rule of thumb the germination temperature (Soil temperature, not air temperature) is about 18°C for most plants at this time of year.

Be aware that most plants need between 14 – 16 hours of sunlight to produce strong healthy stems. If you are germinating on a window sill you can make a simple reflector by covering the inside of a box with tin foil as in photo.
If your seedlings have got leggy you can plant them a deeper when planting out, up to the first leaves on many plants but you’ll have to wait till the next issue for more detailed information.

8 comments
    1. Andrew

      Hi James. Yes, you can start sowing some things but bear in mind most crops need to come out of the plug in approx 4 weeks. This will bring you to the end of March which is still too early to plant out. You can start to sow leeks, early cabbage, spring onion and celery. Don’t forget if you’re sowing celery it needs light to germinate so don’t cover the seeds but keep the compost moist.
      All the best
      Andrew

  1. kevin

    hi i have some lovley plants coming up in plug trays their going good up but not down i have heat and light up to 14 hours day i am watering from the top may be better from the bottem to get a good root or plug any idears
    thanks kevin ryan

    1. Andrew

      Hi Kevin
      Ease off on the watering to make the roots work a bit. Unless are greenhouse plants like tomatoes, cucumbers etc… get them off that heat. I suspect you’ve too much heat and not enough light.
      Hope this helps
      Andrew

  2. Anne

    Hi Andrew,

    We have a fabulous new school garden with raised beds so I really want to make an effort to use them this year. What should/could I sow in seedling trays that I can transplant out and harvest by the end if June.

    I have lots of space in the raised bed so can sow plenty.

    Many thanks,

    Anne

  3. Bongani Nonkanyezi

    Thanks for good article
    Can you please tell me the procedure for making compost for seed tray. I want to make my own seedlings to plant on spring.

    1. Andrew

      Hi Bongani. You can make a good seed compost by working ordinary multipurpose compost through a soil sieve to make a fine consistency. Using bags of old compost is actually better because they have a lower nutrient level which is what you want in a seed compost. I hope this helps. Andrew

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