Seedling Success - My top tips
I have been growing from seed for 20+years now and have made many mistakes along the way. When do you start to sow seeds, what conditions do they need and what are the pitfalls?
Let's start by saying that nothing is for sure, but given the right conditions seeds will grow. It’s very easy to get it wrong with watering, temperature and pests but it’s the cheapest way to fill a garden and will give you many blooms which are not commercially available in the garden centres. You can also ready my Beginners Guide to Growing from Seed - The Dark art of Propagation to start off with.
I start most of my seeds indoors or in my greenhouse at home as they need to be checked on daily and watered regularly. If for some reason I can not get down to my plot one day they will dry out in the heat and die. Some can be sowed direct into the ground but I do find that by planting out sizeable plants that they are much more able to withstand pests and diseases and of course the weather. There are some seedlings which do not like being disturbed though so it is best to sow those direct such as poppies.
So with seed sowing season upon us I have compiled my top tips for successful seed sowing:
1. Do not start sowing seeds too early. It’s very easy to get carried away and sow lots of seeds too early, especially if you have a greenhouse but even if they do grow well at first you will have nowhere to transplant them as it will be too cold outside. Follow the instructions on the seed packet which will often say to sow 10-12 weeks or 6 weeks etc. before the first frosts. Seeds sown later will fair better with increased light levels and will often grow stronger and faster than those sowed too early and often catch them up. I often find that many of my seedlings sowed just 2 weeks apart flower at the same time and also when I sow seed too early it fails to germinate.
2. Moisten your compost first to allow greater absorbtion of watering later on. If you water onto a dry mix you will find that your seeds can easily get washed to the sides of the pot. Just a small sprinkling of water is enough, mix the compost thoroughly and then fill your pots.
3. Tamp down the soil inside your pots a little so that it is compact. Roots don't like large air pockets and will not grow well through them, also It will be much easier to push out the seedling for potting on.
4. Don’t sow seedling too thickly as this will just lead to disease and the seeds will have too much competition to grow strongly. Better to sow as thinly as you can so the roots have plenty of room to grow. This will also make pricking our easier as the roots will not be so much of a tangled mess
5. Check your seed packets. There are vital tips on there for each type of seed. Some seeds need light to germinate and others must not be covered at all. Use vermiculite to cover seeds rather than soil. Soil can form a hard crust on the top of the soil, especially if the seeds are taking a long time to germinate – some can take as long as 3-6 moths ! In general the smaller the seed the less cover they need with seeds such as poppies which are tiny needing no cover and sweetpeas - quite large needing to be buried quite deep.
6. If you can use a heated mat and cloche covers to keep in the moisture. It’s amazing how much quicker they will germinate. Remove each pot as it germinates and grow on in slightly cooler conditions.
7. Always label your seed trays with the variety and date sowed. It can sometimes feel like a long time while waiting for germination but in reality only 2 weeks has passed – which is perfectly normal. It’s also good to test your marker pen to ensure that it is permanent, I have used one in previous years and later found that it was not quite to permanent as the label said it was! If in any doubt then a pencil will work well and will not wash off.
9. Water seedlings from the bottom as much as you can. This will prevent any problems with disease and fungus growing on the surface of the soil and killing your seedlings. You can also use a cinnamon wash to prevent algae. Simply boil a pan of water with a few cinnamon sticks, wait to cool and use this mix to water your seedlings.
10. Take care with watering and feel the soil by popping your finger into the soil to check if they need water. Don’t let them dry out and don’t over water them. Easier said than done I know. Don’t assume that they will all need the same amount of water either. You many need to water some every day and others only every few days.
11. Ensure that you harden off plants well before moving them outside. It is very tempting to just move then from the cosy warmth indoors to get your space back and sow more seedlings but the shock of the wind & rain may kill them. If you can make a cold frame this is the best way to introduce them to the outside world as you can just prop the lid open little by little each day and get them slowly used to outside conditions. Then once you have done this over the course of about 1 week you could take them out of the cold frame during warm days and pop them back in at night before finally leaving them outside after around 2 weeks.
12. Ensure that you prick out seedlings at the right time. Do not prick them out too early, wait until they have developed their first set of true leaves and ensure that you handle them by their leaves not the stalk. Also do not leave them to get pot bound as they will end up a messy tangle as you will not be able to separate them easily, damaging the roots in the process.
13. Remember that the seed sowing compost you used when sowing will only hold enough nutrients for the first few weeks if the seedlings life –up to around 6 weeks so it is important to prick them out and pot them on after a few weeks into a John Innes number 2 or general mix potting compost. If they are still quite small then you can also give them a feed of seaweed fertilizer to keep them going until they are big enough to be moved in to the next size pot.
14. You don't need to sow the whole seed packet! Most seeds will keep for a number of years in a cool dark place so only sow the amount you need! A whole packed may contain 20 cucumber seeds but realistically for the average family you will only need about 5 plants to keep you going all summer long. Courgettes are by far the worst offender, 2 plants are plenty enough for most families and at a push 3 but any more that that and you won't know what to do with them.
15. If you are starting seeds indoors in warm conditiones they can become very leggy. Once seeds have germinated it best to grow then on in cooler conditions if you can - maybe a coolwe windowsill or look at moving then out to a greenhouse on sunny days and bringing then inside overnight.
16. Choose the right container for your seeds. If you are new to seed sowing then you may have to learn as you go through trial and error to see what works for you. There are so many pots and trays out there it can be hard to choose. As a rough guide, the bigger the seed the bigger the pot you need. However I also think about how I want to transplant my seedings and how quickly they grow and the germination rate. So for sweetpeas I grow these in 15cm pots - quite large and deep. I sow about 20 seeds into the pot and they grow quite quickly, they need pinching out once they get to about 12cm tall and staking. The deep pot allows for a cane to be inserted and to stand upright without falling over all the time. Some people sow into deep root trainers or individual smaller cells I find this a bit of a faff when I know that I wil be planting them out with about 5 around each cane support - the roots are pretty tough and can withstand being pulled appart. For smaller seedings such as Ammi or snapdragons I sow these into cell trays with the smallest pinch of seeds I can pick up into each one. They are very fiddly to prick out so this way saves a lot of time. For larkspur and most of my other seeds I use plastic fruit punnets and then prick out into cell trays afterwards as this saves a lot of space early on.
17. Some seeds require a period of cold stratification before they will germinate - The seed packet will tell you this. These are the most tricky seeds and there are a few ways you can do it. These seeds are very hardy and really are best sowed in autumn - this mimmicks their natural conditions. So you can sow them in autumn and just let nature do its job, leaving the seeds outside or in the greehouse over winter. The cold weather naturally kick starts the seeds and once the weather warms in spring they will germinate. The other way is to use your fridge to cool the seeds in spring. I just pop my seed packets into the fridge in Jan/Feb time for a few weeks. Some seeds like to be moist and cold so you can sow them first and then place the pots of the fridge!
19. Some seedlings are a bit tricky to germinate, for me its Astrantia and Bells of Ireand. So what I do with these is sow them onto a paper towel. Spray with water an fold the paper towel a couple of times. I then pop this into a zip lock bag and wait. Sometimes I just place the bag next to my other seed trays or onto a heat mat and if they require cold stratification I pop then into the fridge. I check on them every few days and when they have germinated I remove then from the paper and place into a pot with compost for them to carry on growing!
18. Fresh seeds. Some seeds like to be sowed fresh such as Hellebore and Bluebells. I collect these and sow straight away into plastic fruit punnets and just leave them ouside all summer long, through the winter and then when the weather warms in spring they germinate.