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Blog and News

It's prime time for seed sowing

Parham’s Head Gardener Erika Packard explains why now is prime time for seed sowing and reveals her methods for ensuring successful propagation. 

30th April 2020

Propagation at Parham

It’s prime time for seed sowing, if you haven’t already begun. I start propagation at Parham in January, simply because of the thousands of plants I grow and because we have heated glasshouses to keep plants happy in late winter. However, most home gardeners should wait until March, April, and even May to get started.

Sowing too early, without enough light and heat, is a common mistake many home gardeners make and can result in weak, etiolated plants. Plants grown from later sowings will outperform any you try to start too early under poor conditions.

I recommend following package instructions on depth of sowing and whether seeds need light or darkness to germinate, and to determine their ideal germination temperature. Alternatively there is a lot of information online for starting specific species. Every gardener will have their own techniques for raising plants from seed, and although this is the system that works for me based upon the number of plants I need to grow and the facilities at Parham, don’t be afraid to adapt to your own conditions.

I thinly sow most seeds into mini seed trays full of seed-starting compost after first, and importantly, labelling each tray with the sowing date and plant name. Staying organised is half the battle of raising a large number of plants from seed, and I keep detailed records on each plant I grow, noting everything from its sowing date on until it is planted in the garden. This helps me better plan with each successive year, and starts to build a picture of which plants are most suitable to our conditions at Parham.

Good hygiene and ventilation are also an important factor in your success as they cut the chances of bacterial or fungal infections attacking your seedlings: I disinfect all my seed trays and modules between uses and keep the glasshouses clean and well-aired.

I find a heated propagation mat indispensable, especially as many of our most popular annuals come from warm climates and appreciate some consistent bottom heat to germinate. Don’t obsess too much about ‘perfect’ conditions: seeds are biologically designed to grow, and most common ornamental garden plants are easy to get going.

As soon as the seedlings germinate I move them off heat and prick them out into individual modules in cell trays full of all-purpose compost. Take care to transfer your labels as it is easy to mix things up at this stage, and many young plants look similar. Pricking out is simply teasing the individual plants out of their propagation compost and tucking their roots into their new homes. Many people use dibbers or pencils to help separate the seedlings, but my favourite pricking-out tool is a thin bamboo cane usually sold as a plant support. These canes are strong but lightweight, which is helpful when working through thousands of seedlings, and fine enough to really get in between tiny plants.

Pricking out can be a fiddly job depending on the size of the seedling, which can range from just millimetres to several centimetres according to the species.  I like to prick out the majority of my seedlings at the cotyledon (two-leaf) stage as they suffer less root damage and carry on growing almost as if they hadn’t been transplanted. When pricking out take care to handle seedlings only by the leaves. A plant will replace a wounded leaf but if its fragile stem is damaged at this point, it is game over. Bury the seedling’s stem right up to the cotyledons, which will give you sturdier young plants without ‘weak necks.’ Once you have pricked out your seedlings, gently water them in.

If pricking out doesn’t appeal, you can always sow seed directly into modules or small pots and your plants should germinate and grow on just fine.

At this stage, the most crucial element is enough light. I am fortunate to have several dedicated propagation glasshouses at Parham, but if you are growing at home move your seedlings to the lightest spot you can find.

This time of year it can still be cool, so make sure your plants are warm and protected. With the increasingly long days and growing spring temperatures, they should quickly fill their modules with healthy young roots and put on significant top growth. At this stage they are known as ‘plugs.’ I fertilise my plugs with a seaweed-based liquid fertiliser with most waterings. On warm days glasshouses can reach 30+ degrees and without much compost around their roots plugs grown in modules are vulnerable to rapidly drying out and dying. I check on and water the plugs several times a day, especially in warm, sunny, and breezy weather.

I monitor my plugs as they bulk up and once their roots are developed enough to hold together as a solid mass, but before they become root bound, I pop them out and pot them up into nine-centimetre pots of all-purpose compost and continue to fertilise them with most waterings.

Once the roots have filled these larger pots it should be warm enough to harden them off for at least a week by gradually exposing them to the outdoors and wider temperature and light conditions. Then your young plants should be ready to plant out and enjoy in the garden.

Words and photos by Erika Packard