I recently attended another excellent talk by Ray Broughton, hosted by my local Horticultural Society. Ray shared his tips on how to sow seed which I will attempt to explain in detail in this post. I’ve been pretty successful sowing seed in the last couple of years but found myself learning a lot from Ray’s advice.
Firstly you need to make sure your compost has the right moisture content. Take some compost and squeeze tight in your hand. If, when you open your hand it crumbles away and falls on the bench it is too dry. Conversely if it drips water when you squeeze it’s too wet. If it stays together in the palm of your hand then you’ve got it about right. Just keep mixing until you’ve got the moisture right and you won’t need to water after sowing and risk disturbing the seed you’ve just sown.
Secondly seed compost is relatively expensive so don’t fill your tray up with it. Use cheaper potting compost for the majority and the more expensive seed compost for say the top 1/4″. For germination the relatively sterile, nutrient poor, seed compost is ideal but to support early growth seeds require the nutrients they will get when the radical pushes into the main body of the standard potting compost.
You will need a collection of sterilised convection trays. Convection trays have the holes on both the raised and depressed surfaces on the bottom of the tray. This allows the tray to draw up water through the holes flush with the bottom of the tray whilst allowing water to drain from the holes in the depressions on the bottom of the tray so preventing the seedlings from ‘drowning’.
There are different methods for sowing fine seeds (e.g. marigolds) as opposed to medium sized seeds (e.g. lettuce). Firstly fine seeds. Fill your tray 3/4’s full with standard potting compost. Then generously mound your seed compost over the top well over the top of the tray. I made a simple tool out of plywood to match the inner dimensions of my trays for the next stage (not sure of the proper term for these).
Using this tool held vertically carefully scrape the excess compost off the tray. Now with the tool held hoizontally press down firmly with your weight evenly distributed. This firms up the compost ready for sowing.
Now for the seeds. With fine seeds never handle them. Put enough seeds into a plastic cup to cover an area of a 1 pence coin. Now add silver or sharp sand to an area roughly the size of a 2 pence coin and mix together by shaking the cup gently. The sand makes it easier to see the distribution when you sow onto the darker compost. Sow directly from the cup as evenly as you can across the tray. If you oversow and get a large blop of sand in one area there is a nifty trick to pick up the seed. Here’s the science bit, not sure if I can get this right. Seed has a negative charge (or is it positive?). Rub an ordinary bic biro pen a few times on your clothing giving it a positive charge. Put this over the area of sand that has been sown too heavily and the seeds will leap up onto the pen. As soon as you re-adjust your feet you’ll earth the charge allowing you to brush the seed off the lid of the biro onto the area of compost you want them. Genius really! The picture didn’t come out to well but you get the idea.
Now once you are happy with your distribution of seed that’s it, no need to cover fine seeds. If you’ve got your mositure content of the compost right there should be no need to water in. Keep an eye on the moisture level say at day 3 and use a fine rose or mist spray if needed, by this time the radical should be on it’s way (the radical grows before the shoot) and the seed is therefore ‘rooted’ in the compost and shouldn’t be disturbed by your watering as long as the rose is fine enough. A couple of tips here as watering can roses are expensive. Why not use some cheap flour seive material cut out and fixed around your rose to get a finer spray. Or cover your tray with fleece and tuck underneath the tray, then water with as fine a rose as you’ve got. The fleece will make the spray finer as it goes through to the compost.
For medium sized seed there’s no need for sand and you can handle them as they are more robust than the finer seeds. You can add flour if you want to lighten the seed so you can see it better on the dark compost. Put the seed in the palm of your hand and tap lightly as you move your hand around the tray. Place paper around the tray so you can catch any seed that misses the tray. Remember seed is relatively expensive so it’s worth taking time over this part of the process. And if you have oversown an area use the biro trick to pick up the excess seed and re-distribute.
Unlike the fine seed the medium sized seed needs covering with compost – as a rule of thumb only enough compost to cover the thickness of the seed is needed. I have been using far too much in the past and burying seed. Place some compost in a 2mm sieve, as I’ve said you don’t need much. Hold the sieve level with your mouth and move the seive over the tray. Start and finish outside the edge of the tray, you can sweep up the compost off the bench afterwards, it just means you get an even covering right to the edges of the tray. The reason you hold the seive so high is so you can see what’s happening on the surface of the compost. Hold the seive to low and you haven’t got a clue how deep you are burying those seeds. Once the last seeds disappears stop, that’s all you need. Again no need to water in if you’ve got that moisture level right.
You can use vermiculite or perlite as a medium for sowing onto. Advantage here is that both take on, and retain, water and are sterile mediums. Vermiculite is more expensive than perlite but you can get a lot of dust with perlite which you need to be wary of unless you sow in a well ventilated space. Vermiculite will expand with water up to 10x its’ size and will bond to the surface of the compost. I have used vermiculite before sucessfully, it is derived from organic source but is not strictly organic I suppose as it has been processed. For fine seed you can sow directly onto vermiculite on top of potting compost. As with the compost method press the vermiculite down creating a flat area to sow onto. You will struggle to see the light seed against the vermiculite, if this is a problem dye the seed in beetroot dye, it will stay red once dry so you can easily see where you’ve sown.
One last thing that I didn’t really think about until now is hygiene when sowing seeds. How many times have I been messing about with the compost or manure and then gone straight in the greenhouse and sown some seeds transferring I don’t know what disease across. Always wash your hands thoroughly before sowing to prevent this from happening, latex gloves aren’t a bad idea either.
Well that’s it, hope you’ve found this useful and best of luck!