Growing Healthy Vegetable Seedlings

Vegetable seed propagation supplies

Seedling plug plantGrowing your own can be tricky business for someone new to vegetable gardening but there are a number of ways you can stack the odds of a successful harvest in your favour. My number one would be to start your seedlings off indoors in modular trays where they have a better chance of survival and of producing a strong and healthy vegetable plant. The magical transition from seed to seedling is a rocky road for baby vegetable plants so, just like us, it makes sense to protect them in their early stages of life.

Most vegetables, with the exception of root crops like carrots and parsnips, will do much better if started off indoors and planted out at about 4-6 weeks old. It makes sense to┬ástart seedlings off in a protected environment so they don’t have to face the elements in their early stages and can be planted out when conditions are more pleasant. There are things you need to look out for when growing vegetable seedling plants indoors but they do bring you a little bit closer to the elusive dream of hassle free vegetable growing!

If you’re relatively new to growing you can start off with some easily grown vegetable plants like lettuce, rocket, kale, spinach and chard which are perfect to start off in modular trays.

Here’s my top 4 reasons for growing healthy vegetable seedlings indoors:

Protection
Most seeds are started off in Spring when the weather can be erratic with swings from warm spring sunshine to wind, rain and damaging night time frosts. It’s a hostile world out there in Springtime so the warmth and protection of indoor sowing will definitely get you off to a good start.
Protecting your precious plants from slugs and snails is another big bonus as a single slug can easily wipe out rows of tender emerging seedlings in one night leaving you wondering if the seeds germinated in the first place.
Also, don’t forget a greenhouse or tunnel is a nicer place for your plants to be in early spring but it’s also a much nicer place for you to be too! Get you growing year off to a far more pleasant and comfortable start.

Young vegetable seedlings in a seedling plant trayHeat
The ideal temperature for germinating most vegetable seeds is between 18-20 degrees celsius. Warm climate crops like tomato plants will prefer a warmer 24 degrees which you’re highly unlikely to get outside in an Irish spring!
Early seedling plants are started off in a propagator, on a heat mat or on a south facing indoors windowsill and can be planted out when the weather warms up in late April or early May. Later sowings in April can be germinated and brought on without extra heat as daytime temperatures in the greenhouse or poly tunnel will be much higher than outside. It’s worth remembering frosts of -3 or -4 degrees will penetrate plastic or glass so a roll of horticultural fleece will be handy to cover tender plants when frost is forecast.

More crops over the year
As soon as one crops has finished a new vegetable can be planted which has already been a month underway indoors. You are saving 4 weeks of valuable growing space in the garden meaning you get more from the growing season.

Get ahead of the season
It’s never a good idea to get stuck into the vegetable garden too early and as we’ve already covered it can be impossible to sow many plants outdoors until the soil warms up. If you sow outdoors in late April or early May you still have 4 weeks to go before your plant reaches a healthy seedling stage. If you plant 4 week old vegetable plants at the same time of year then obviously you are a month ahead which is important with our short, wet Summers.

Plastic modular seedling traySowing in Modular trays
For me modular trays are the best way to go to produce high quality vegetable seedlings for the garden. Modular trays are plant trays with individual cells for each plant which vary in size depending on what you want to grow. Modular seedling trays have a number advantages over the traditional method of growing in seed trays.

The modular tray produces individual vegetable plug plants in a little ‘plug’ of compost. There will be very little root disturbance when the seedling is planted out as unlike a standard seed tray the roots won’t be tangled with the neighbouring plant. You will also find modular trays, particularly the 84 cell, very handy for moving your seedling plants when hardening off. It’s much easier to pick up one tray of 5 or 6 different varieties than gathering up separate seedling pots.

Here’s a quick guide for sowing in trays below, if you want to give it a go I also include a list of items you’ll need for best results:

84 Cell Plant Tray 3 Pack.
Gro Char Seed Compost 8 Litre.
Bottle Top Waterer 4 Pack.
Your Choice of Vegetable Seeds
Seedling Labels – Pack of 50
Garland 2 in 1 Soil Sieve
Small Vitopod Heated Electric Propagator
Large Vitopod Heated Electric Propagator

84 cell modular seedling trayWe use 84 cell seedling trays which give a seedling plug of about 2 inches in depth, we find these the most versatile trays in our seedling nursery. Clearly you won’t need 84 of each plant so sow 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.

Using a fine seed compost for growing seedlings in modular traysUse 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 can hinder germination and damage new seedling roots.
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.

Make planti g holes in seedling trayWith 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. As a rule of thumb the sowing depth should be 4 times the diameter of the seed.

 

 

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.

Scrape excess compost frok seedling trayCover 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.

 

 

Watering an 84 cell seedling plant trayGently water your seeds. A good tip is to use a plastic bottle with small holes punched in the cap or a bottle top waterer. 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.

Seedling Care
If you are germinating seedlings in a greenhouse or tunnel before the beginning of April (sometimes and of April depending on the year) you will need a heat source like an electric propagator or heat bench to germinate the seedlings. As we’ve mentioned most seeds will germinate happily at temperatures between 18 – 20 degrees, anything below this when the weather is cold and the seed is likely to rot in the compost. A soil thermometer will be handy here but the best method is a heat mat, heat cable or propagator with a thermostat.

The thermostat can be set at the desired temperature meaning the heat source will only turn on when the temperature falls below the set heat. Your greenhouse or tunnel is likely to be above 18 degrees on a sunny day even if it’s cold outside so you need not waste electricity having your heat source powered on.

Leggy elongated vegetable plantsLeggy Seedlings
The most common problem beginners have when growing vegetable seedlings is plants becoming long and spindly or ‘leggy’. This happens when the plant gets enough heat to germinate but not enough light for healthy growth. The seedling will try to increase it’s height quickly to find a strong enough light source to survive and this results in weak elongated plant stems. After all there is only so much growth a seedling can manage so what the plant gains in height it sacrifices in the width of the stem.

Leggy seedlings are a problem because the weak stems won’t stand up well to wind and rain and are more prone to pests and disease. If you have very long leggy seedlings you are better off disposing of them and stating again for most crops. If your seedlings are elongated but can stand up on their own it may be possible to plant them a little deeper and cover a large part of the long stem. This can only be done with certain plants as I’ll show in the ‘Planting Vegetable Seedlings’ article.

Preventing Leggy Seedlings
As you have probably guessed by now the way to prevent leggy seedlings is to make sure they get enough light.

If you are starting seeds off on a windowsill a South facing window is best as this will get the most light from the sun. It is also worth placing a reflective foil behind the seedlings to help reflect the sunlight and ensure the plants get more even exposure.

If you are using a heat source like a propagator or heat mat in a poly tunnel you need to get them off the heat source. The heat is only really required to germinate the seedlings and once the first new shoots come up they can be taken off. Growth will slow down and hopefully leggy plants will be avoided.

Watering vegetable seedlings with a watering canWatering Vegetable Seedlings
Treat em mean! Over watering is a much common reason for failure than under watering so be a little stingy with the hose. The compost needs to be more damp than wet as a wet growing medium excludes air needed by the roots which ‘drowns’ them and causes them to rot in the plant trays. Also, a slightly dry compost will make the plants work harder and produce more extensive root systems as they search out moisture. Give your plants a good work out and produce a fitter, stronger plant.

However (there’s always a ‘however’) don’t let compost get too dry which causes it to form a crust on the surface which can be difficult to re-wet. You’ll know of your compost is too dry as you’ll see it pulling away from the edges of the pot or seed tray module.

Protecting Vulnerable Seedling Plants
Vegetable plant trays grown in an unheated greenhouse or poly tunnel can still be affected by cold as temperatures below -3 or -4 degrees will penetrate glass or plastic. We use cheap and effective horticultural fleece which gives excellent protection, use a double layer in a very hard frost. If you live in a particularly cold area you may need an electric or paraffin heater set on a thermostat but we have never found the need to use one.

Wooden cold for for hardening off seedling plantsHardening Off Seedling Plants
Seedling plants intended for outdoor planting need to be slowly introduced to outside temperatures before they can be planted out. How would you like it if you spent your life sitting by a cosy fire in a nice warm living room and someone suddenly decided you had to live outside? Plants who have to face cold and wind that they haven’t experienced before will certainly struggle to survive.

What to do? Use a cloche or cold frame to slowly introduce pampered seedlings to the big, bad world. A cloche is a removable cover which can be placed over your young seedling plants to protect them from the worst of the weather. If the weather is fine leave your plants in the open but make sure to cover them if cold, wet or windy in the first few days. Gradually leave them out for longer until the last day when you can leave the cover off at night.

A cold frame is handier as you can progressively open the lid a little more to gradually expose your plants. Guess what? We have a very nice timber framed version with twin wall glazing for extra insulation.

Wooden cold frame for hardening off vegetable seedlings

 

Wooden raised garden pond shop

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3 Responses to Growing Healthy Vegetable Seedlings

  1. Mary Whelan says:

    This is a great information site. Many thanks. Mary Whelan

  2. J. Bogans says:

    I always thought growing seedlngs was very difficult, you laid it out nicely and make it seem achievable.

    • Andrew says:

      Hi there. I am delighted you found our article easy to understand, I hope you have a great success with your first seedlings. Please feel free to get in touch if you need any more help. Good luck! Andrew

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