How to sow seeds in pots and trays indoors
As Spring approaches your thoughts may well be turning to the upcoming growing season and how to prepare. One way you can get a head start is by getting some seeds growing in a warm environment whilst you wait for the outside conditions to become more stable. I have written this hub to explain how to successfully start seeds indoors and maximise your chances of producing plenty of healthy young plants that you can ultimately transplant into your garden once the soil is warm enough and the risk of frost is past.
Sowing and growing plants from seed is far easier than you might imagine so please don't be scared of trying this at home. You don't need a greenhouse, just a sunny windowsill to move the germinated seedlings to so they can grow on until they are old enough to be planted outside. Growing your own plants from seed can save you a huge amount of money, with each resulting plant only costing you a tiny fraction of the prices a plant nursery or garden centre would charge you for an older plant. What's more you can always swap your surplus plants with friends and neighbours, or you could even organise a 'Plant Swapping' event so the whole community can take part.
The first thing I will point out is that a packet of seeds goes a very long way, especially if the seeds are very small, so you might not want to plant the entire packet (unless you are considering swapping or selling your surplus plants.) The other thing you need to remember is that if you are growing certain vegetables you might not want to have a glut of these ready to eat all at once, e.g. lettuces, so only sow small amounts of these seeds at any one time.
Don't forget that many seeds can be planted directly into the ground once the weather warms up, so by starting off some seeds indoors you are simply giving yourself an earlier crop. It won't necessarily mean those types of seeds need to be started off indoors throughout the entire growing season.
Read your seed packet
When you buy a packet of seeds the first thing you will need to do is read the packet. This will clearly state if the contents are suitable for starting off in pots or seed trays, or whether they should be sown direct into the ground where they are to mature. Certain seeds like carrots, radishes and beetroot will only be suitable for sowing direct into the soil, (mostly because they are root crops and do not cope well with transplanting). One slight exception to this rule is actually parsnips, but only because you can improve the germination rates by germinating them indoors on damp kitchen towel contained within a plastic sandwich bag. When they germinate carefully sow the germinated seeds into pre-watered drills on your vegetable allotment. Other seeds are ideal for starting off indoors, (and in some cases it is virtually essential) for example tomatoes, lettuces, runner beans, courgettes and cucumbers.
After you have established the seeds in your packet are suitable for starting off indoors you need to check that if you plant them inside now the recommended 'planting out' date will not be too far away. The last thing you want is an outsized plant on your windowsill when the recommended 'planting out' date is still three weeks away. If you plant it out too soon the young plant may well die, and if you keep it in the pot or tray too long there is a risk the plant will exhaust all the nutrients in the compost or will become sickly and stunted due to overcrowding with the surrounding seedlings.
Next check the seed packet to see if these are seeds that should be covered over with compost after planting or if they should be sown on the surface. Quite often you find very small seeds are better off on the surface of the compost because the shoots don't have to push through any barrier to reach the light. Each seed only carries enough nutrients to allow a shoot to grow approximately two and a half times the height of the seed before the food supply runs out. Very tiny dust-like seeds have no chance of making it to the surface if you sprinkle even a fraction too much compost over them so they are ideal candidates for surface sowing.
Prepare your plant pots or seed trays
Depending on the nature of the seeds you are sowing you will either need some 3" plant pots or some small seed trays. If you are really ambitious you could buy some modular trays (trays divided up into small modules / cells allowing for one or two seeds in each module / cell).
- Open a bag of good quality seed compost, and (because it is usually quite compacted within the bags) use your hands to crumble it up to a breadcrumb type consistency.
- Fill your plant pots or trays to the top, and then give them a sharp tap on a firm surface to settle the compost. Using a ruler or a flat piece of wood skim any surplus compost from the top of the pots or trays.
- Gently firm the surface of the compost using a flat object such as a small section of a wooden plank.
- Take your prepared pots or trays outside, then use a watering can to thoroughly water them and leave for twenty minutes to drain.
Time to sow your seeds
Now comes the fun part, the actual sowing of the seeds themselves. Depending on the size of the seeds the method will be slightly different. You might enjoy this article on 'How to Sow/Plant Seeds Large and Small' for more in depth instructions. Let's start with large seeds like courgettes or runner beans. These will normally be grown in three inch pots of compost.
- Firstly use your index finger to poke two holes in the compost about two and a half times the height of the seed.
- Carefully place a seed in each hole ensuring it is the correct way up.
- Sprinkle some fresh compost into the holes until they are full to the top.
- Use a trigger spray to dampen the extra compost you have added to the holes.
- Using elastic bands or string tie a piece of cling film over the surface of each pot. Alternatively place all the pots on a tray and use a piece of glass to cover all of them at once. A third method is to place all the pots in a plastic propagator which will keep the moisture in.
- Label the group of pots with the date they were planted and the seeds they contain.
- Place the pots on a hole free tray (to avoid water getting everywhere) in a pleasantly warm location such as your kitchen. At this stage for most seeds sunlight will not be necessary (although double check your seed packet as a few seeds need sunlight to germinate.) I prefer to keep them out of direct sunlight until they have germinated because this helps to prevent the compost drying out.
- Every day or so you will need to remove the glass or the plastic propagator lid and wipe the condensation from the inside of them to avoid problems with diseases later on. This is also a good time to make sure the surface of the compost is still damp, (which it should be). If for any reason it is drying out, then use your trigger spray to lightly mist it with water before covering the pots again.
- As soon as the seedlings break through the surface of the compost take off the cling film or plastic/glass covers and move them to a well lit windowsill.
- For the next week or so try to avoid watering the pots from above. Far better to stand them in a shallow tray of water for a while and allow osmosis to draw the water up through the compost. Once you see the surface of the compost has moistened remove the pots from the water and replace them on their original hole free tray.
- By now you should be able to see the two seedlings very clearly, and you can determine which is the stronger of the two. Remove the weaker seedling in order to allow the stronger one to grow on unhindered.
- Once your seedlings have developed their first full sized 'true' leaves and the plant is established, you will want to start the 'hardening off' process. Hardening off reduces the risk of shock to your plant when it is planted out into its permanent position. For at least ten days move your pots into the garden in a sunny spot, but bring them indoors again each night. Alternatively move the pots to a cold frame or unheated greenhouse and ventilate during the daylight hours. All going well you can then safely transplant your young plants into the garden with a minimal risk of them either dying or suffering from any setback in growth due to shock.
How to sow very small seeds
Smaller seeds can be a little bit more complicated to plant but there are some easy ways to get around these difficulties such as mixing small seeds with tea leaves or fine sand before sowing them. The general rules are not dissimilar to those applied to large seeds with a few obvious exceptions.
- Start with a seed tray of compost prepared as instructed earlier.
- For seeds like lettuces, cabbages, cauliflowers or tomatoes space them out over the surface of the damp compost.
- Gently cover the seeds with a few millimetres of sieved compost, or a thin layer of either vermiculite or perlite (latter both available from your local garden centre or plant nursery).
- Cover with cling film, glass or place in a propagator in the same way as described for the larger seeds, (again wiping away any condensation that forms on the inside surface every day or so.)
- Follow the exact same instructions as for the large seeds until your seedlings are about two weeks old. At this point you can thin them out by removing any overcrowded or weakling seedlings. If you are careful healthy but overcrowded seedlings can simply be transplanted to an area of the tray that has more space (or to a new tray).
- Once your plants have established their first true leaves transplant them into individuals pots or modular trays and grow on in a greenhouse or cold frame.
- Harden off as described earlier before transplanting outside.
With the very small dust-like seeds, e.g. lobelia and aloe vera you will almost certainly need to find a good way to sow the seeds thinly. These really tiny seeds are usually sold in small pieces of folded up waterproof waxed paper because the seeds are too small for foil lined seed packets. I have my own method of sowing such small seeds and it works very well.
- Quarter fill a trigger spray with water and tip the dust-like seeds into it, (you might need to blow on the greaseproof paper to dislodge any left behind).
- Agitate the water in the trigger spray to mix the seeds throughout the water.
- Simply use this water to spray the surface of one or two seed trays (making sure the setting on the trigger spray produces a mist, not a jet.) As the water is distributed so are the seeds.
- Do not cover with anything other than the cling film, glass or plastic propagator lid, i.e. no compost.
- Follow the same directions as for other seeds from here onwards, (although it will take quite a lot longer before the seedlings will be large enough to thin out or transplant.)
Sowing into modules (an alternative method to mine)
A slightly different method
So there you have it. Hopefully reading this will have left you feeling far more confident that you too can successfully start your own seeds indoors. Just remember when you plant out your young plants to keep the soil moist for a week or so until they establish a healthy root system that can reach deep down into the soil and find its own moisture. Once the plants are growing well do not water too often or you will encourage a very shallow root system. What you actually want are healthy roots that are reaching down deeply to find their own moisture (where it is most likely to avoid evaporation.) Use mulches around your plants such as spent compost, straw or seaweed to help conserve moisture in the soil.