Reaching the crucial part of the whole exercise, Ian Hodgson looks at seed sowing techniques.
A forest of strong, healthy green seedlings is every seed sowers dream and a measure of the skills required to coax dormant seed into life. It need not be an elusive dream, the fancy, coloured picture adorning many seed packets can become a reality by just mastering a few basic techniques.
The right materials and attention to hygiene are the keys to the seed-raisers science.
Pots and containers should be cleaned thoroughly before use. Compost caked to the side of the pot can harbour diseases. Washing with disinfectant and a few drops of washing-up liquid or a proprietary brand of garden cleanser should do the trick. Rinse over all containers with clean water before use.
Seed sowing compost is a matter of choice. It should be free draining, yet capable of holding sufficient moisture to allow the seeds to germinate. Never use potting composts for seed sowing. They contain high levels of fertiliser which can burn sensitive young roots or will cause seedlings to grow abnormally quickly.
As a general rule, peat based composts offer far more flexibility. They are light, easy to handle and less variable in composition. Other types of compost may contain a variety of substances mixed with peat, such as the minerals, vermiculite and perlite, or even shredded bark.
A simple but effective compost can be produced by mixing equal parts of sphagnum peat and fine horticultural grit or sharp river sand. Never use builders sand as this may be contaminated with lime. A preference for a particular type of compost will become evident after a few seasons' experience.
There are a bewildering array of pots and containers suitable for use. If you are unsure which size to go for it is better to sow in too large a pot than be tempted to sow too thickly. Overcrowded seedlings will be thin and weak and make bad plants. Large seeds can be sown individually or spaced equally in trays.
When preparing the compost in the pot or tray, the idea is to produce conditions as uniform as possible to ensure that the maximum amount of seed germinates.
Fill the containers loosely with compost until it is slightly proud of the rim. Strike off the excess with a piece of wood to leave a level surface. The compost should now be compressed to form the seed bed. For this operation a flat-bottomed wooden press is required. The compost should be compressed so that a gap of about 1 inch (25mm) is left round the container, enough to allow for top-dressing and watering. Homemade presses can be made from oddments of timber shaped so that they will just fit into the container at this depth. A piece of wood nailed to the back of the press will allow better handling. Too small a press will cause uneven pressure and thus variable conditions for the seed.
Often the most critical stage of the whole process is the act of transferring seed from the packet onto the compost. For many, enthusiasm can turn to horror as the precious seed is spilled onto the floor and to oblivion. Many of the pit-falls can be side-stepped by planning your operation. Have all your containers filled and prepared and other equipment ready and waiting before opening the seed packet. Always read the instructions on the packet first. They will usually tell you how and when to sow as well as highlighting temperatures required for germination. Certain types of seed may need special preparation before sowing, such as soaking in hot water for a period of time, so only open the packet when you are good and ready. Enthusiasm should not get the better of you.
Unless you are sowing in-situ, always sow seeds in sheltered conditions in the greenhouse or indoors. The kitchen table of many keen seed-raiser has become an impromptu potting bench at certain times of the year. Before opening the packet, make sure that the seed is opposite the end being opened. The packet itself is now used as a dispenser. Cutting off the corner, tip the packet forward slightly tapping it so the seeds fall out of the opening. Whilst you are doing this, move the packet slowly over the compost, so the seeds are broadcast evenly. The tip of the packet should not be more than 2in. (50mm) from the compost surface otherwise seed may be lost. Alternatively, one side of the packet can be pinched to form a beak along which the seeds can be targeted onto the compost.
Unless very large, avoid handling seed with your fingers. Sweat from your fingers contains a variety of acids and chemicals which can damage thin walled seeds, even preventing them from germinating.
Uneven sowing can be rectified by gently teasing seed into gaps using a blunt knife or blade.
Many plants, such as calceolaria and lobelia have exceptionally fine seed. Seed companies frequently wrap up fine seed in small inner packets. These must be opened very carefully and the seed sown as normal.
Failure to firm the compost in the corners of the seed tray is a common fault and leads to shrinkage after watering.
Many people have problems sowing fine seed and there is no doubt that it is difficult to sow evenly. To help bulk up the seed, simply mix it with a small amount of fine and above all, dry silver sand. This mixture can then be sown in the normal way.
Fine seed need not be covered but larger seeds should receive a thin covering of sieved compost or Fine grade vermiculite. Again the seed should be firmed in using the hand press.
When the seeds have been sown they should be watered in. Pots containing larger seeds can be watered in from the top using a watering can with a fine rose. Fine seed watered in this way may get washed into deep crevices in the compost only to be lost. These containers should preferably be soaked in a bath of water. Ensure that the water level does not come over the sides of the pot flooding the surface of the compost. Leave them to soak until the surface is evenly wet, then lift them out and allow to drain. Alternatively, water the compost in the pots or trays with a fine rose first and leave to drain before sowing your seeds.
As a precaution against damping off diseases, seeds can be watered with a fungicide, such as ‘Cheshunt Compound'.
Algae, liverworts and mosses will tend to cover the surface if the pots are left for any length of time. Plants whose seeds germinate erratically or seedlings which are of exceptionally slow growth will quickly be engulfed by these primitive invaders. To prevent this from happening the surface of the compost should be covered with a thin layer of fine gravel or grit. Never use builders sand as the lime content may damage seedlings and it also forms a crust, acting as a physical barrier to the young plants or starving them of oxygen.
The seed should now be placed in a position where they can germinate. Information regarding ideal temperatures is usually written on the back of the packet or can be found in a variety of textbooks. If growing in a greenhouse, pots should be placed where they receive sufficient heat and light. A thermometer inserted into the compost will give an indication of temperature. If you're sowing early in the year you may need the services of a propagator where conditions can be more carefully controlled. Covering the seeds with newspaper or a sheet of glass will help maintain higher temperatures and conserve moisture. Seeds which require exposure to cool temperatures can be placed outdoors under the protection of a cold frame.
Slugs love to graze on young, succulent seedlings and a night of their attentions can be catastrophic. Take the precaution of protecting your seedlings by using a suitable slug bait or control in and around the pots.
Ian Hodgson trained at Kew and is now Technical Editor of Practical Gardening magazine.
Source of article
Growing From Seed - Summer 1988 Vol. 2 Number 3
© The Seed Raising Journal from Thompson & Morgan