Raising Plants from Seed

This is a follow on article to “Basis methods of seed sowing”

There are many ways of sowing seeds, from sowing directly, to sowing in trays or pots or in modular or cell trays. In recent times raising plants indoors and transplanting them later has become the favourite method for many reasons as outlined below.

Direct Sowing

In theory all vegetables can be sown directly into the ground where they are to grow, and thinned out to their final spacing. Generally speaking root crops such as carrots, beetroot, parsnips, swedes and radish don’t transplant well and are usually sown directly into the ground. Transplanting those crops may cause forking of their roots (especially carrots). Also vegetables with large seeds (peas and beans) are generally sown directly.

Direct sowing requires a very fine soil (remember some seeds are tiny!) and a well prepared an weed-free bed. The soil needs to be warm enough for the seeds to germinate in the best possible time. In reality this means that often seeds can’t be sown before the middle of April.

Sowing in trays or modules

Most gardeners therefor prefer to sow in trays and modules. The seedlings or transplants are potted on or planted out 4 - 8 weeks after sowing. Most vegetables benefit from transplanting and there are many advantages of this method:

· good crop establishment

· uniform plant development

· faster transplanting, thus reducing labour

· easier weed control

· shortens the growing period in the garden

· used for seeds which are difficult to germinate in the garden (e.g.celery)

· less wastage of seeds - no thinning is required.

Having the seedlings in trays or modules on a work top or heated bench in the polytunnel or glasshouse means you can look after them much easier and can protect them better.

Stages in raising plants

Sowing
Pricking out- if seeds are sown in open seed trays (ward trays) they are pricked out (moved) into a larger container so the seedlings have more room to develop.
Potting on- moved into an individual pot - to get high quality plants for planting out.
Hardening off- so that plants can gradually adapt to lower temperatures and windy conditions. Obviously hardening off is unnecessary when growing in a polytunnel.
Planting- when the plants are fully hardened off they are planted out into their final position. During hot spells it is advisable to plant out in the evening or choose a dull day.

(Some of these stages can be by-passed)

The need of a propagator or a heating mat

Seed germination generally benefits from a permanent temperature with a good average of 16-22 C. Heating mats offer a very even heat distribution and can be used to heat propagation benches/shelves or propagators. Soil warming cables put in sand can in our experience at best deliver 18 C. Therefore the best option in our view is a heating mat as you can buy the size that fits your purpose from 40x120cm (85W), 60x120cm (140W), 60x200cm (263W) & 100x200cm (300W). We have a heating mat in our polytunnel of 80X300cm. Another advantage is that they can be easily rolled up and stored if the shelves/benches are needed for other purposes. These mats include a temperature sensor and a thermostat for precise heat control. They are not cheap but are for life! We have ours for over twenty years! With this devise you can sow seeds all year round at the ideal germination temperature.

Seed composts and nutrient requirements

You will need seed compost and potting compost and the advise is to buy good quality organic and peat-free compost. As the name says, seed compost for sowing seed into and potting compost for transplanting.

Germination will take place without any nutrients - indeed better than with nutrients. However, seedlings require a balance of the main nutrients (Nitrogen, Phosphorous, Potassium.) as well as trace elements to sustain plant growth for a short period. High levels of Nitrogen will inhibit germination or produce leggy seedlings. As the plants develop they require more nutrients for their growth. When potting on the seedling a richer compost should be chosen or alternatively liquid feeding will be necessary.

A good seed compost should be: