Carol, Carols Garden
Sowing Success - The Basics
All seeds are designed to grow. They want to grow. You just need to provide them with the conditions that they need in order to grow.
They need water, warmth and (to a greater or lesser degree) light - either to germinate or very soon after they have germinated. The vast majority of seeds are very easy and will germinate readily. Annuals are often the easiest - their survival strategy depends on their ability to create lots of viable seed and for it to germinate quickly and freely.
Some perennials or more tropical varieties might be a bit harder or take longer. They may need more specific requirements for heat or light/dark, amount of moisture etc.
Some seeds have in-built protection mechanisms to ensure they don't germinate at the wrong time for them to grow. This is called dormancy. This might mean that they are programmed not to grow at the time and in the conditions you want. Some seeds have a physical protection eg a hard outer shell which needs to be soaked or chipped to allow water in, and some have a chemical one which may need a period of cold to break down the chemicals and allow the seed to germinate.
These are generally designed to ensure the seed does not germinate until spring, when there is sufficient warmth, moisture and light to allow the seedling to thrive. There are some seeds which need to pass through the gut of a bird (to ensure they germinate away from the parent - often a feature of trees) or need to be exposed to smoke (plants which germinate in the space created after forest fires).
The most common though, are those needing a spell of cold similar to a period of winter. This is called Vernalisation. These are often the seedlings that pop up in spring or summer, all on their own eg astrantia, delphiniums. If in doubt, try to replicate the natural way that a seed will fall and germinate. Seed packets often give you precise germination requirements for dormant seeds, but they can be tricky. One way to avoid this can be to collect fresh seed, before it has entered dormancy. If you collect Astrantia seed as it is just starting to turn brown and sow it straight away, you will, most likely, get very good germination.
Happily though, the vast majority of seeds don't need such careful treatment. They need:
Moisture - Seeds take in a lot of water when they are first sown, and this is what can trigger them to germinate. They will need a good quality growing medium which retains moisture without being too wet (which might cause the seed to rot before it grows). Ideally this will be weed- free to allow the seed to get established without competition. If you're sowing inside into trays or modules, this is easily achieved with a good quality sterile seed compost.
Warmth - precise requirements vary, but hardy annuals will generally germinate at anything above 6C. But they will be slow and may rot or be eaten before they get going. A good benchmark for quicker results is 15-20C for most seeds. A few will need higher than this especially if they are tropical. A few will not germinate if temperatures go too high.
Light - some seeds need light to germinate, but some germinate more easily in dark conditions. When sowing indoors, a light covering of fine vermiculite seems to allow a good balance of light to allow most seeds to germinate. Most seeds will, however, germinate without good light, so you can start them in enclosed dark spaces, such as stacked in a propagator, but you do need to check them at least once a day and be ready for the next step.
As soon as seeds germinate…
Once germinated, seedlings need continued light, moisture and warmth. They need less warmth and more light at this stage. You need to balance warmth and light. Leggy seedlings result from too much warmth for the light available. Cold seedlings just don't grow (although sometimes their roots are still growing)
(Leggy seedlings of Gypsophila below, these were sown on a heated bench too early in the season, so although it was lovely and warm on the bench, the light levels weren’t high enough for the rate of growth, so the seedlings have become stretched or etiolated)
Timing is all!
Don't sow until you know what you're going to do with the seedlings once they have germinated. Do you have the facilities to keep them growing? Do you have space to pot them on? Or to plant them out? Work out when you want them and work back to when you need to sow.
These are Gypsophila seedlings sown at the same time that weren't grown on heat, the corner modules are disturbed as these are the perfect size for pricking out.
Viability, Storage and Pre-chitting.
To retain best viability, store seeds in a steady cool temperature. A fridge is an ideal place (and it usually keeps out vermin). The worst conditions are being too hot (so the seeds dry out completely) or repeated warm and cold conditions which may cause condensation and allow the seeds to rot or to try to grow. You can test viability by putting seeds in water. Viable seeds are more likely to sink. (but then you'll have to sow them straight away). If you want to be sure of viability, you can pre-chit seeds on wet kitchen towel. This allows you to test what germination rate you can expect, but also means that you can just sow the ones which have germinated, saving compost, and space.
Sowing Direct outside
The simplest way to sow seeds is to just scatter them on the ground. This might well work, so long as the seeds get enough light, moisture and the right temperature. This is what seeds do naturally. But a lot of seed can be wasted and the plants have to fight it out for themselves. When we sow in our plots, we are using valuable seed and we want as much of it to germinate in the place we want as possible - and for it to be able to thrive and grow on quickly. Light, sandy soils are best for direct sowing (ie good weed-growing soils!) as you can easily get a soft friable tilth and they don't often stay wet and cold for long. But, they do germinate weed seedlings just as easily. Heavier or stony soils may need more work to get them to a good condition to sow.
Top tips for when and how to direct sow
When the soil is warm and moist - spring and autumn sowings germinate bes. Minimum soil temperatures apply as mentioned above - over 6C, or ideally around 15C
Sow when the weather is dry, water in the drill only (give it a good soak) and keep the surface of the soil dry. Resist watering again until you're sure it needs it. Keeping the surface dry will reduce the number of weeds that germinate.
Consider creating a ‘stale seed bed’ - prepare the bed a week before you need it. Let the weeds germinate and hoe or burn with a flame weeder in dry weather, just before you sow. This will eliminate some of the surface weed seeds.
Prepare the soil well so you can cover the seeds with just a fine layer of soil, not big lumps of soil.
If you need to water, keep it to just the rows of seedlings, leaving the gaps dry.
Keep weed seedlings down by regular hoeing until your plants are established.
Thin out/transplant as required.
Station sowing can also save on seed - this is sowing just a few seed at
each ‘station’ where you want a plant to grow eg at 9” intervals along
the row. You can also do this by sowing direct into holes in sheets of weed membrane, although beware or increased slug and vole risk.
What plants to direct sow:
Things which germinate easily and quickly
Where you've got plenty of saved seed
Things which resent root disturbance
Plants which can be closely spaced and are fiddly to transplant
Big, reliable seed which you can place where you want them
Paula sows - Sunflowers and Sweet peas - in heavy clay soil in Scotland direct sowing isn't usually viable
Claire sows - Phacelia, Nigella, Corncockle, Poppies for seed heads - in chalky soil in Surrey direct sowing should be good, but slugs take some of the crops
Carol sows - Cornflowers, Nigella, Larkspur, Opium poppies, Agrostemma, Grasses, Annual Gypsophila- in sandy Cheshire soil direct sowing works well, but need good maintenance and weed control.
Sowing Inside into trays or Modules
Most of us sow seeds inside - in propagators, on heated benches, in greenhouse/polytunnel and cold frames. Almost always, we are sowing seeds into trays, modules, soil blocks etc in compost of some kind.
The advantages of starting seeds this way are:
Better control of the growing environment - providing the heat and light that some seeds need.
Getting a head start on the growing season - to sow much earlier than you could outside. This allows us to get plants ready to plant out when the weather is warmer - so we get earlier crops, and we can grow crops which might need a longer season than we naturally have in the UK
Often much better germination rates than direct sowing - especially important if we are growing bought seed. We don't want to waste expensive seed on feeding the slugs!
Best use of bed space - we can be growing seedlings on to the right size to plant out whilst the bed space is still being used by an earlier crop. We can make better use of growing space this way and can get two or more crops per season, which wouldn't always be possible if we sowed direct.
Means we can start early in the year and feed our need to get sowing, when it''s way too cold for direct sowing!
Sowing in pots, trays and blocks - the options
You can sow into pots, trays, module trays, soil blocks. When you're deciding which to use for what, think about:
Small pots or trays - take up less space on a propagator, so they're good for early sowings, or anything you think will be difficult or to germinate, or will germinate unevenly, or you’re only sowing a few eg perennials. The disadvantage is that you will need to prick them out. But you don’t use much compost.
Sow direct into modules or plugs - good for when you’re sowing in spring and expect quick and easy germination. The size of module is a trade-off between getting the plants big enough to plant out, but not using any more compost and space than necessary. I use 60-cell deep module trays for most annuals, 84 cell for some small and quick growers eg grasses, poppies, annual gyp, bigger pots for big growers eg cosmos, sunflowers. I will sow two or three seeds per module and just thin them out as necessary. This is quick, means we don't have to prick out or handle the seedlings again until they're ready to plant and is economical in seeds and compost. The disadvantage is that you need lots of bench space to lay the trays out.
Sow into soil blocks - these are a way to avoid use of plastic trays and can be a great way to save compost and make best use of space. I only use the micro blocks and use them for:
1. Quick and easy germinators in peak season - and plant out into beds straight from the micro blocks eg Nigella, poppies. Very efficient, but you do need good growing conditions for them to grow away, and at just the right time - you can't keep them long in the blocks.
2. For seeds which need heat and time, so it's a space-efficient way to get lots of them on the propagator eg lisianthus, Icelandic poppies in winter.
Micro soil blocking video - apologies for me having a cold and it was very cold in the shed!
What next?
So, your babies have hatched?! What to do now?
Once they have germinated, seeds will need good conditions to keep growing. They will grow best if they have the right amount of warmth, light, water and nutrient. If they are short of any of these, their growth will be checked, and they may then take some time to recover, if at all. Judging this takes observation, vigilance and experience. You will learn to spot signs of problems quite quickly - becoming pale, or leggy, or dark/dull, or in the worst case, keeling over or shrivelling up! Just remember that they do want to grow (sometimes despite all evidence!), you just need to learn what they need. The next stages are.
If they are direct sown, in the ground - keep them watered if they need, keep them weeded/hoed. Thin them out so they have space to grow (maybe in two stages to be confident), transplant a few if you've got gaps. Stand back and watch!
If they are in pots or trays, you will need to prick them out into module trays or individual pots. Most seedlings need to be able to grow into their own space and develop a self-contained network of roots before they will cope with being planted out into the ground.
If they have been direct sown into modules, just keep them watered, moderately warm and in good light as above. You may need to thin the seedlings to one per cell, or even transplant a couple to fill any gaps. Once the roots have just filled the cell so the compost retains its shape, they are ready to plant out into their final place, so long as weather conditions allow.