Welcome to my potting shed! This is the column where I’ll share all my gardening hints and tips – and I’ll try to answer any queries you may have.

I grow dwarf lilies in containers. This year they have grown tall and spindly but the flowers are normal except for some which have almost grown to about two feet with tiny buds, which haven’t opened. What’s causing this problem? – Jeanette Leckie, by email.

Too much shade is usually the cause of lanky stems. Lilies need at least six hours of bright daylight to perform. Start again next year with fresh bulbs and compost and grow the lilies in a sunny position, keeping them well watered.

Destroy any rose leaves showing signs of

blackspot. Pick up any that have fallen as the spores overwinter in the soil.

Last year I repotted large phormiums that had become potbound. Since then they have put on little growth and the foliage is a sickly yellow. Why are they not thriving? – Mrs Emma Murison, Bathgate.

If you tip the phormiums out of their pots, you will find they haven’t sent any roots out into the new compost. Tease out the roots before replanting and soak the pots for an hour in a deep container filled with water. Apply a dilute feed weekly.

Sow borage seeds for beautiful blue

flowers that are a magnet for bees.

Some of my tomato plants have flowered but the fruits haven’t developed. Why is this? – Jack Rogers, Beith.

Hot weather can cause problems with fertilisation, especially in greenhouses. Use greenhouse shading and open vents when hot temperatures are forecast.

Prune plum trees now, taking out

diseased and dead wood and cutting back branches.

I have large, bright green bugs on my hydrangeas, almost triangular in shape. Will they cause any damage? – Irene McAllister, Oban.

These are our beautiful native shield bugs and most of them do little harm.

To increase stock or rosemary plants,

take cuttings now, inserting them into compost mixed with sand.

Some of my roses are covered in a white substance and the leaves have begun to fall off. – Calum White, by email.

This is powdery mildew, a fungal disease, that strikes roses with dry roots. Sprays made from baking powder and liquid soap are recommended.

Courgettes growing in containers

should be watered twice a day.