Dear Sibe,

Is it possible to start growing sunflowers indoors before putting them in the garden? Will this help them grow bigger?

Freya

Our Gardening Expert replies:

Hello Freya,

Sunflowers, (Helianthus annuus) are annual plants that could certainly be started indoors in say a 4in (10.2cm) plant pot before planting them out into the garden. This would be useful if you had a very cold soil or were prone to late frosts. As to whether this would help them grow bigger really depends on how skilfully you can manage the transition between growing in a pot and planting out into the open garden.

Normally, seeds are sown directly into the ground where they are to flower in April. When exactly in April depends on weather conditions at the time but the earlier the better. If planting directly outside you can always cover the seeds with a cloche or jam jar, or even a large transparent plastic lemonade bottle with the bottom cut off so it can be pushed into the soil, protecting the plant from slugs and increasing the soil temperature.

If you do sow them indoors you will find that they soon become drawn by the low light conditions and could grow quite rapidly. If they get too big the plant will never grow as well in the ground as it would have done by sowing directly outside. If you are entering a competition and want to go to a lot of trouble to get the biggest sunflower in your area then you could try the following method but as a safeguard I would always sow a few seeds outside as you'd be surprised how well these can do without the shock of being transplanted.

Sow the seeds one per pot into 4in (10.2cm) plant pots and make sure you have sown more than you actually need in case of accidents. Use a loam-free compost and ensure this is thoroughly moistened before placing the pot into a plastic bag and putting into a warm place such as an airing cupboard for three or four days. Examine carefully twice a day to see if the seed is showing signs of germinating - you'll see it starting to push the compost upwards if this is the case and then immediately take out and place in the brightest position you have available indoors. As soon as seedlings actually emerge make small holes in the plastic bag to allow more ventilation then gradually make these bigger as the plant develops, eventually taking the bag off completely. Keep the plant well watered and turn daily to ensure it grows vertically.

Then if you can plant outside do this as soon as possible. You need a fertile soil cultivated so that it is friable for at least a foot around and below where the plants will go. Pre-warm the soil by covering with a sheet of plastic for at least a week. Make a hole using another pot of similar size, water the plant thoroughly then gently tip upside down with your fingers around the plant but not touching the stem. Remove the pot and try to turn the plant over and place it into the hole in the ground without losing any compost. Gently firm the surrounding soil so that there are no air gaps between the compost and the soil layer then water thoroughly with warm water before covering with a cloche cover or whatever you are using. Take precautions against slugs and as soon as possible when the plant has hardened up a little, after ten days or so, take the cover off and liquid feed on a weekly basis.

Happy gardening!

Sibe

To keep unwanted visitors away from your Sunflower (Helianthus Annuus) see Pest Control and Snail Trail. And if you like the idea of growing plants indoors see Houseplant Heaven, Houseplant Humidifiers and Indoor Garden.