Glasshouses and Propagation

Before you can start to propagate and grow any plants, it is important to examine your glasshouse and make sure that it is ready to use.

During the previous year, pests and diseases will have lodged themselves into the framework of your glasshouse. To minimise the risk of diseases affecting your plants it is essential to clean and disinfect the glasshouse before you start to grow anything. It’s best to use a cleaning solution of water and a disinfectant such as Jeyes Fluid. Use the manufacturers recommended dilution and always use protective clothing and rubber gloves. Using a brush with a bucket of the solution or a spray bottle, thoroughly clean all areas of your glasshouse, including any benches and be particularly careful when cleaning the glass panels.

Many of the plants that you will be propagating are not frost hardy so you will need to insulate and/or heat your glasshouse to protect them. The best method of insulating your glasshouse is to line it with bubble wrap. You may also need to use a heater and there are various glasshouse heaters available including electric and paraffin fuelled models. Electric heaters will need to be kept dry however the benefit is that they can be thermostatically controlled.

Once you have cleaned and insulated your glasshouse, you are ready to propagate your plants. The two main methods of propagation at the start of year are seeds and cuttings. It is important to use good quality compost especially true when sowing seed. If you can, use a specialist seed and cuttings compost as this will be low in nutrients (this will prevent the new roots of your plants from becoming burnt) and will be made up of finer materials. Remember to always sieve the compost when filling your container and the container you use should be appropriate for the size of seed being sown.

For large seeds such as sweet peas, use a cell tray and sow each seed into its own cell. For finer seeds, use a seed tray and mix the seeds with some horticultural sand. This helps to spread the seed evenly and reduces the need to thin out at a later stage. Once this is complete cover your seeds with a thin layer of sieved compost or use a layer of vermiculite.

It is good to take cuttings of plants such as Fuchias, Penstemons, and Geraniums (Pelargoniums). It is easier to take cuttings January/February as you only have to over winter a few plants rather than over wintering many cuttings. When taking cuttings, always use the new young growth as these will have the greatest chance of success. Remove a shoot from the plant about 2 inches long with a ‘heel’ at the bottom. Remove the bottom leaves but leave the shoot tip. Only remove this once the cutting has rooted. Place these cuttings into filled containers. Again, use seed and cuttings compost if you can, and mix in some perlite to increase the drainage.

Once this process is complete you are ready to place your seeds and cuttings into a propagator. Doing so will dramatically increase the amount of plants that you can propagate, e.g. 500 seedlings or 200 cuttings a fortnight. Put a layer of peat in the bottom of the propagator (this helps to spread the heat evenly) and line the lid with horticultural fleece (this helps to prevent condensation dripping down on to your plants.) Leave seeds in the propagator until they have germinated and cuttings until they have rooted. When ready remove them to prevent them from becoming stretched and weak. This also helps your plants to harden off in readiness for growing on and planting out.

So, to recap the main points:

  • Clean and disinfect to help prevent disease
  • Use a good quality compost
  • Use good quality seed and young healthy cutting material
  • Use a heated propagator set up as stated above
  • Remove your seedlings and rooted cuttings to a cool, but frost free place, to prevent them from becoming stretched and weak

By following this guide, you can create a colourful summer garden to be proud of.