I LOVE blue flowers. Each year, I make a trip to a bluebell wood near the village of Horndean, in Hampshire. This year, the flowers were past their best when I got there, but, since then, there has been blue everywhere. A ceanothus bush planted in hope in the garden has bloomed mightily; there are forget-me-nots, grape hyacinths, and now the agapanthus is just coming into flower. Soon, there will be blue hydrangeas.

There are various shades of blue in the world of flowers, but I am particularly drawn to those that remind me of sapphire. There is something unearthly about the shade, which points to a perception of heaven.

Years ago, when I climbed Mount Sinai for my television series Lives of Jesus, I was struck by the intense blue of the sky above the Sinai desert and its contrast with the red dustiness of the region. No wonder the ancient Israelites, on their journey to the Promised Land, assumed that God’s permanent dwelling was in the sky over Sinai. No wonder Moses and Aaron, Nadab and Abihu, and 70 of the elders of Israel approached God on the mountain top, and saw him with the sapphire pavement beneath his feet, “like the very heaven for clearness”.

Sapphire mirrors the sky, as do our spring and summer blooms. Some traditional medicine attributes to sapphire a capacity to calm the mind and heal mental distress, and, in Jewish tradition, sapphire stands both for wisdom and protection.

In the teaching of the fourth-century hermit Evagrius, the human mind has the capacity to “see its own state in the time of prayer resembling sapphire or the colour of heaven; that state scripture calls the place of God which was seen by the elders on Mt Sinai”. On a recent visit to Newcastle Cathedral, I noticed that the new altar and ambo are built round a deep and shining blue interior, like the stricken, streaming rock.

It occurs to me that, although we eat fruit and vegetables of many colours, we don’t consume much that is truly blue — blueberries are too dark to count. Blue is beyond the flesh; it is where grief and heaven meet.

Penelope Fitzgerald’s novel The Blue Flower is about an aristocrat obsessed with the notion of a perfect blue bloom. It is based on Novalis, a key figure of German Romanticism. The blue flower stands for a mystical fulfilment at odds with the frustrations of real life. Novalis was tormented by a romantic attachment to a young girl far less well-educated than himself, an attachment that came to an end with her early death.

So, perhaps the blue flower contains a warning as well. Do not try to anticipate heaven in this life, but keep attending to the beauty that is here, with all its promise and its limitations.