How to Sow

Nothing to it? Well, yes and no! We are after all just putting seeds into compost and adding water – so what’s the fuss? Well, we make life difficult because we want to grow a wide range of vegetables and most of them would not grow in our cool, damp climate without our assistance. First we have to get the seeds to germinate and then we want them to grow vigorously.

What’s Germination?

The first thing a seed needs to do is absorb water, then if the temperature is within a given range (this varies with the vegetable variety) and it’s the right time of year, it will start to grow. The seed will swell up as it absorbs water and assuming the conditions are right then the seed case will split and the radicle or primary root will emerge. This attempts to anchor the plant in the soil/compost. The radicle is followed by the embryonic shoot, this grows upwards towards the light.

Swede seedlings waiting for planting out

Lettuce seeds just germinated

Now the structure of the soil/compost is really important at this stage. The root network developing from the radicle needs to make contact with the soil particles to get anchored, continue absorbing water and get ready to absorb nutrients. The shoot needs to penetrate the soil structure vertically and reach the light so that the leaves can open and start producing food.

Until the roots have made good contact with the soil particles and the leaves are open, the plant has to rely on the food that was stored within the seed. If the food in the seed runs out before the seedling starts making its own, then the seedling’s growth will be stunted and it will possibly die.

On the left are some Lettuce (Marvel of 4 Seasons) seeds that have just germinated - they have taken about 6 days to reach this stage. I started off with 4 seeds per 4ins (10cm) pot of peat free multi-purpose compost. I will thin out to the strongest in a week or two (or if there happen to be two good ones separate enough I will re-pot them both).

Humus for the Perfect Soil/Compost

What we missed from the above description is the seedling’s roots must also have access to air. So the soil structure must be open enough to allow air to circulate (and excess water to drain away), whilst the particles need to be small enough for root hairs to get up close to them to absorb necessary water and nutrients from them. The access to water needs to be pretty constant too, so the soil particles need to hold water. Humus is the key here. This is the coating of organic material that envelops each soil particle (usually particles of rock). Humus is made from rotted down plant material and as well as providing a great environment for micro-organisms and other tiny creatures it acts as a reservoir of plant nutrients and water. Maintaining high levels of humus is a gardener’s top priority if vegetables are going to be successfully grown over many consecutive seasons.

Are you Chitting me?

Ok, so why don’t we just drop the seeds into a glass of water and then stick them in the compost?

Firstly, it’s not a bad idea to soak seeds for an hour or two in tepid water. It means that the compost does not have to be so moist and this lessens the risk of damping off (see later). Ok for Broad Beans and Peas but some seeds e.g. Celeriac are like dust and getting them out of the water would be tricky. I have found that some seeds germinate much better is they are "chitted" first. Sweet corn is a good example of this. I put the seeds between damp kitchen roll on a plate above the water heater. Within 48 hours you can see which seeds have germinated and then sow them. You could do this with beans and peas too.

Size Really Does Matter

Basically the bigger the seed, the deeper you plant it. Broad beans can go 2 ins. (5cm) into the compost whereas smaller seeds (such as Celeriac) should be simply sown on the surface and gently watered in. A rule of thumb would be to bury 2 times the seed size.

Optimum Conditions

Right, we now know that we need to provide a compost that has the right structure and we know what depth to sow the seeds. What about temperature, light, watering and feeding? These four factors need to be kept in balance to maintain steady, healthy growth. Generally speaking, whatever the light is doing, the others should follow.

Temperature

Most seeds will germinate successfully over a range of temperatures. The majority will be perfectly happy around 10 -14C. Vegetables from warmer climates will typically want to start off at 20-25C (Tomatoes, Peppers and Aubergines for example). The further the temperature is away from a plants optimum germination temperature, the slower and more erratic germination occurs. Ideally we want all the plants to come up together so we can deal with them as a batch. So, read the directions on the back of the packet for the correct germination temperature. Electric propagators are a really useful investment as they last years and if they have a thermostat, can give you a decent amount of control. Just remember that all propagators can only provide heat. A propagator with a thermostat cannot keep a plant cool on a sunny day and may do a nice job of prematurely cooking your crop! For this reason, if you think a day is going to be sunny, provide some shade from direct sunlight.

As we traditionally do most of our sowing in spring, we are usually blessed with lots of cool, grey days and if we leave our seedlings with too much heat they will often start to grow tall and spindly. Once the seeds have germinated its best to lower the temperature a little – the aim for just about all vegetables is to grow compact, dark green plants.

Light

Unless you invest in artificial lighting, this is the factor least under your control. There is no doubt (other things being equal), that crops grow best in a sunny year. Generally in summer light is not a problem in the UK, but in early spring and late autumn the short (often cloudy) days slow down growth considerably. In the spring we will have lots of seedlings growing and if we don’t adjust the temperature and watering to match the available light, problems will quickly occur. So on sunny days, you should water more, less when it’s cloudy.

Water

Too much water is just as damaging as too little. Any seedling stood in cold, wet compost is going to struggle. Such conditions also encourage the growth of moulds that can rot plants off at ground level – so the top can look good but the seedling will keel over and quickly shrivel (this is known as damping off). Wet compost looks darker than a dry one. A quick glance will tell you if the compost is dry as it will look lighter. If you are not sure push your finger tip into the seed tray or plant pot.

When applying water be careful not to wash the seeds and/or the compost away! Small seeds are light and an over-vigorous watering will wash them down the sides of the plant pot. Use a fine spray on a watering can where possible. Also it’s a good idea to fill the watering can up first and let it stand to cool down or warm up to the ambient temperature – this prevents the plants being stressed by a sudden change in temperature.

Food

Seeds come with an included food store that will be enough to get the seedling up and running. Depending on the size of the seed/seedling within a few days the plant has to get its basic food requirements from the compost. Most compost has enough nutrients to last 4-6 weeks. After this, if the plant has not been planted out or re-potted it will be necessary to add extra feed – often this is easy to give in liquid form.

Healthy plants

The whole point of taking all this trouble is to get the maximum germination rate (from the increasingly expensive seeds) and grow the sturdiest plants. Fast growing plants invariably produce the earliest and most prolific crops.

Its important to thin most sowings to give enough space for each plant to flourish. Not many plants grow well clustered together. If you thin early enough by splitting the compost with a plant in each section you can re-pot and get two or three healthy plants from the original sowing.

When planting out try to avoid disturbing the roots - plant out before roots start growing out of the bottom of the pot.

Lettuce Seedlings - 30 days.