Outdoor Classroom: Sowing seed in trays

Photo 11) Sowing seed should save you money, especially with vegetables and annuals and it is also the way of getting plants which may not be available otherwise – such as dwarf daffodils, English snowdrops or rhododendron species. We use polystyrene mushroom trays which we have been continuing to use for up to 20 years. Wooden or plastic trays can also be used but you need around 10cm in depth and plenty of drainage holes. Egg cartons can be used for quick turn around crops such as lettuce or peas. You can also reuse the punnets that come from garden centres. Mark likes small individual pots for vegetables.
Photo 22) It is preferable to use proper seed raising mix which has less fertiliser in it than potting mix because fertiliser can burn young plants. These mixes are sterile, so you know when you see shoots that it is your seeds germinating. You can use garden soil if you want to but coarsely sieve it first to get rid of larger lumps and you need some fine sand or similar to sprinkle over the seeds on top. A home made sieve is fine. You can’t use unwashed beach sand because plants don’t like salt. A bag of seed raising mix is easier and goes a long way so is not expensive.
Photo 33) When filling with mix, tamp it down to get rid of air bubbles by pressing on top of the tray. If you are using egg cartons or individual cells, sharply rap the container on a hard surface to get the mix settling further. However, if you are using garden soil, don’t compact it.
Photo 44) Large seed can be hand placed but fine seed is traditionally tapped out of the hand as shown in the photograph or dispersed in small quantities from a piece of folded paper. It can also be dispersed by pinching it between fingers like salt.
Photo 55) Spread a thin layer of mix on top of the seeds. The smaller the seed, the lighter the covering but almost all seeds need a complete cover (primulas and rhododendrons are an exception. These are surface sown – ie not covered). Water carefully. A misting bottle (a well-washed window or shower cleaner bottle with a pump spray) is ideal for fine seed. A watering can with a fine rose to disperse the water is also good. Don’t flood the seeds.
Photo 66) Label the tray. We favour a soft pencil and hard plastic labels which we scrub and reuse for years. Pencil lasts longer than marker pen and is easier to clean for reuse. Precious, fine seed can then be covered with a protective sheet of glass. Stretched plastic can also be used. Until seeds germinate, place the seed trays out of direct sunlight and in good light. It is usually wise to elevate the seed trays away from slugs and snails or cats who think it is a litter box. Check your seed tray daily for moisture levels but do not scratch around looking to see what is happening. When the seeds have germinated, move the tray to sunny conditions and increase the watering as required.