Now it is March it is time to think about sowing seeds. Whether you want to grow some bedding plants, a few perennials for the border or some vegetables, March is the time to make a start.
But before you do, it is important to get to grips with the basics to make sure you are successful. Seeds are good value but they are not ‘cheap’ so it is vital that they get the best start. Despite what you may sometimes be told, there are sometimes problems. So, with apologies to those of you who are ‘old hands’ at raising plants from seed, I want to describe the main principles. This is all about sowing seeds in warmth, in the greenhouse or on the windowsill.
I will deal with seeds you can sow direct where they are to grow (such as root crops and hardy annuals) in coming weeks.
Seeds vary in their needs but most of those you are likely to grow all need similar conditions.
The main reasons for failure are seeds drying out, seeds being waterlogged, the temperature being too cold, fungal disease killing seedlings, poor light killing seedlings, slugs and woodlice, and rough handling. If this seams a long list, do not despair.
What you need
Seed trays – for seed sowing you do not need deep containers. Small seed trays or ‘cell trays’ are best. These must be new or clean. If you use dirty pots or trays they will be infected with disease (or have slugs on them) and that results in failure.
You can use recycled plastic containers such as meat trays, yoghurt pots etc. but you must make holes in the base before you use them. Toilet-roll tubes are OK for sweet peas and other large seeds like beans and sweetcorn but I find them awkward to use and to fill and hold upright. And you can just add them to the compost heap anyway. They may be useful for transplanting and growing on plants as are ‘peat’ pots (now made with coir and alternatives).
Compost – the compost must be fresh and free from disease. Buy a new bag and do not use ‘leftover’ compost from last year. Seeds do not need high nutrient levels to germinate so do not use ‘mature plant’ composts. In theory John Innes Seed sowing compost is fine but the quality is rarely as good as it should be so I would avoid it for most seeds (cabbages being an exception).
Vermiculite – this expanded rock (along with perlite) is added to compost to ‘aerate’ the compost, improving drainage. I would add between 10% and 20% by volume to the compost, especially for ‘delicate’ seedlings. You do not need to add it if sowing large seeds like courgettes or beans but it is useful for antirrhinums or rudbeckia which hate waterlogged compost. It is also useful to cover seeds – it allows light to reach the seeds, which is often beneficial, and keeps humidity around the seeds as they grow.
Water – always use tap water when sowing. Water from a water butt can be contaminated with fungi and bacteria
Sieve – a sieve is useful to prepare a fine surface for sowing. But you can often use a flower pot – put some compost in the pot and shake over the sowing area. Or you could use an old colander.
Propagator – seeds need warmth to germinate. A temperature of about 20c (from 15-25) is ideal to germinate most seeds. Any lower and seeds may just rot in the cold, wet compost. Any higher and seedlings may become ‘stretched’ and difficult to handle. You can buy an electric ‘heated’ propagator and those with a thermostat are best to avoid excessively high temperatures on a sunny day. But you can cover the seed pots or trays with a clear plastic cover of any kind. In the greenhouse you can simply cover with a sheet of plastic or fleece – to retain some heat and moisture. You will need to remove and shake the plastic covering every day to remove excess moisture. Propagator lids will have ‘vents’ so you can gradually acclimatise seedlings to outside conditions. Never let plastic sheets lay on the actual seedlings or they will be prone to rotting.
Watering
it is often suggested that you water your seeds or seedlings with a ‘mister’. This is usually a bad idea because keeping the seedlings constantly moist will lead to ‘damping off’.
Damping off is a fungal disease that ‘creeps’ through the compost and will kill the seedlings at soil level, causing them to ‘topple over’. It can kill all your seedlings in a few days.
Regular misting will make matters worse. It is best to water the trays before sowing. You may then not need to water again for at least a week and usually not until the seedlings appear – then water by placing the seed trays in a tray of water so you water them from below and do not get the seedlings wet.
Constant misting and watering soaks the compost, the tiny roots will die in the airless conditions and the seedlings will die. It also encourages fungus gnats, the tiny ‘flies’ that are common around overwatered houseplants.
Not all seedlings are especially prone to damping off but small and delicate seedlings are very prone and they tend to be the expensive seeds such as petunias and antirrhinums!
So, on to practicalities
When to sow
As soon as the seedlings appear they will need to be transplanted into pots or cell trays to grow on. They will then need good light and some warmth to grow. If you are sowing on a windowsill you need to prepare yourself for this – one pot of seeds may become a hundred pots of plants! Most bedding plants are frost-tender. They cannot be placed outside until mid-April and not planted till Mid-May. If you sow too early you will struggle to keep your seedlings healthy and ‘sturdy’.
This is a common problem with sunflowers. Sown in March in yoghurt pots they will soon be seedlings and by mid May, when it is safe to plant them out, they will be poor, straggly, weak plants, starved and tied to canes and will never make good plants. Delay sowing till mid April.
Seed packets will give a range of sowing times but late sowings always catch up (within reason) and are best if you are sowing on the windowsill. If you have a greenhouse, where light levels are higher, you can sow a bit earlier. Even with a greenhouse I do not sow most bedding plants till early- to mid- March. I sow tomatoes around the 20th of March (for growing in a greenhouse) and I sow cosmos (which grow quickly) and my cucumbers (which hate cold, wet conditions) in early April. I sow courgettes and sweetcorn in Mid April and zinnias and hardy annuals about the same time.
It is also important to ‘harden off’ seedlings before you plant them. I am getting a bit ahead of myself here but it is important that your seedlings are acclimatised to outside conditions before planting them out, especially if they have been grown in the home. Without wind and direct sunlight they will be ‘soft’ and will scorch when suddenly planted outside. So move them outside on cloudy, mild days in late April and bring them back in on cold nights. Think about how your body reacts when you go on holiday – after being covered up for 50 weeks what happens when you lay in the sun all day when you finally get to Malaga?
So, to recap
Fill your trays. Fluff up the compost, mixing in some perlite if you like. Fill the trays loosely and tap them to settle the compost. NEVER press it down. Watering will do all the firming necessary. Brush off excess with your hands and pick off large lumps. If your compost is wet and has been outside for ages avoid using it. Always buy fresh compost for seed sowing.
Then water the trays before you sow. You can put them into a tray of water to soak them if you have time. Let them drain for a hour if possible. Always use clean tap water.
If you want to or if sowing very small seeds you can sieve over some compost but this is not usually necessary for most seeds – it will depend on the compost. You can do this before or after watering.
Sow the seeds thinly. This will make them easier to transplant later and will make damping off less likely. I tend to sow a packet over several cells in a tray so that if damping off attacks some seedlings it cannot spread to them all. You do not always have to sow the whole packet – if stored cool and dry the seeds will last till next year. And if there is a disaster you will have some more to sow.
You can then cover with sieved compost or a thin layer of perlite or vermiculite. You do not need to water again so you will not be washing tiny seeds into the compost.
Seeds vary hugely in how long they take to germinate and it will vary with temperature too. Cosmos and marigolds will be up in a week, others will take several weeks. Your aim is to produce sturdy seedlings. As soon as they are ‘up’, start to ventilate them so they are not in stuffy, humid conditions.