Number 45, Sandford Terrace, Ranelagh. For so many people, that Dublin address represents a sort of horticultural rite of passage, a place of pilgrimage where a generation of the country's gardeners have been enlightened and informed; their tastes honed, and their eyes opened to the myriad of exciting, intriguing possibilities that come with the act of making a garden. That generation includes me. There are so very many valuable lessons that the Dillon garden, and its makers, horticultural luminary Helen Dillon and her husband, Val, have taught me since I first visited it in my early 20s.

One of the very first is generosity. As a young, enthusiastic, not terribly knowledgeable gardener, I'll always remember the day I first stood in this half-acre Dublin garden (not long after it had first opened to the public some 25 years ago), covetously admiring a particular plant for its large, heart-shaped leaves edged with silver freckles, which looked as if someone had used a fine paintbrush to daintily embellish them. Its name (I didn't know it then) was Brunnera macrophylla 'Langtrees', a shade-loving, spring flowering herbaceous plant that you can now track down on the internet with a few simple clicks of the mouse. But cast yourself back to a time when there was no internet. When there were no Irish specialist nurseries or plant fairs as we now know them. When good Irish gardens that were open to the public were like hens' teeth and most Irish garden centres carried a pretty limited range of plants. In other words, when the chances of buying a plant like Brunnera 'Langtrees' in this country were close to zero.

Back to a time when I was a young gardener staring at a plant, wondering at its delicate beauty and how it came to grow so happily in this amazing Dublin garden. Which is when Helen appeared and inquired in the friendly way she did – and still does with everyone – whether I was enjoying myself, and whether I had any questions. Somewhat awestruck, I asked her the name of “that plant” and whether she might possibly have one I could buy? She told me what it was called, adding kindly that she didn’t have any potted specimens for sale. I must have looked slightly crestfallen, for a little while later she reappeared, this time holding a small pot containing what was clearly a division dug up from the parent plant just moments earlier. I was so overcome with embarrassment and gratitude that I don’t remember what I said. But I’ll always remember that generous act.

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Since then, and like so many Irish gardeners, I’ve learned so much from the Dillon garden. Big philosophical lessons that stay with you for the rest of your gardening life, such as the importance of bravery and a certain devil-may-care attitude when it comes to good garden making. And how important it is to create a garden that gives you joy, and how constant editing is at the heart of all great gardens, whether it’s discarding the plants that bore you or excising those garden features that are somehow dissatisfying or disappointing. And why all of us, as gardeners, should be so very wary of the potential tyranny imposed by our own perceptions of what constitutes “good taste”. Which includes the silliness of being a plant snob. And why all good gardeners should hone their eyes to recognise a good garden-worthy plant when they see it, whether that means rescuing it from someone else’s compost heap, or from the side of the road (great plants have come to the Dillon garden in exactly these ways). And of course, the importance of colour in a garden in terms of its ability to alter our mood and create atmosphere.

But it has also taught me a host of other practical, mud-under-the-fingernails garden lessons. Such as how crucial it is to choose garden-worthy varieties that have proven themselves to be floriferous, long-flowering, robust and vigorous. Or why we should value certain self-seeding plants in a garden in terms of their ability to create rhythm and repetition. Or why we shouldn’t be afraid of growing tall plants. Or how simplicity within a planting scheme – such as the repeated use of Betula ‘Fascination’ in the Dillon front garden – is so satisfying and restful to the eye. Even something like how a relatively humdrum plant, such as the old apple tree that grows in the Dillon back garden, can be utterly transformed through ingenious pruning techniques so that it becomes a piece of living sculpture. I could go on. And on. But I won’t. Suffice it to say that I will miss this bold and brilliant Irish garden, which opens its doors to the public for one last time tomorrow. Do go and see it while you still can.

See dillongarden.com

This week in the garden 

Put on a fleece As night-time temperatures begin to fall, the use of garden fleece can help to prolong flowering displays of tender annuals as well as other autumn flowering plants such as dahlias. But if you already have some fleece, don't leave it to the last minute to start rummaging around in the shed for it. Find it now, while there's still plenty of time, and if it's grubby, pop it in the washing machine on a short cycle before putting it aside safely to use in the coming weeks when frost is forecast. Fresh supplies are also available from most good garden centres.

Beware evil weevils If your garden suffers badly from vine weevil damage, it's worth considering the use of a biological nematode control such as Nemasys Vine Weevil. Applied now while soil temperatures are still high, it attacks the white maggot-like larvae of the weevil, which cause terrible damage to the root systems of infested plants. A live product, it must be ordered in advance before being dissolved in water and applied as a drench to the soil. Available from most good garden centres including mrmiddleton.com

Sow grass seed If you're planning a new lawn or want to repair bald or damaged patches in an existing one, any grass seed sown now will germinate quickly and evenly. But always make sure to prepare the soil well in advance so that it's clear of stones and debris, even and raked to a fine tilth. Different grades of lawn seed are available with some more hard-wearing/ drought- tolerant/slow growing than others. Ask your local garden centre for advice on which mix is best suited to your need