This week, this little unassuming fella helped me pass through a milestone.

It is Pellitory-of-the-Wall, a native plant that normally grows at the foot of walls where there seems to be not a crumb of soil to support it. But it popped up out of nowhere in my Bee Border, and became my 500th type of plant in my garden this year.

Other newbies for my list this year include Wild Parsnip, which has now flowered in the wildflower meadow for the first time...

...and this gorgeous thing which came up in the vegetable patch, which I originally thought was Common Fumitory, but has larger flowers and is more sprawling and turns out to be Common Ramping Fumitory.

In 2014, when I took on the garden, I recorded 222 species of plant, which gives you an idea of how things have developed (and perhaps hints at my plant obsession!).

The two things that have really made a difference are the cornfield annual beds (the poppies and the like) which this year had perhaps 40 or more different plant species in it, and the wildflower meadow which has a similar number, including the Common Knapweeds which are blooming for the first time this year, here this morning with Meadow Brown supping away at the nectar.

Plant diversity is the bedrock of biodiversity, and at last gardens are being recognised for the value that can come from the fact that they contain so many different different types of plant. As Jennifer Owen says in her book, Wildlife of a garden - a 30 year study, "A gardener crowds together in one place a far greater diversity of plants than is ever found in one place in the wild. Even in tropical rainforest, an area equivalent to that of a typical garden would not contain so many species."

Much of this diversity we bring in by choice. My Hemp-agrimony may be a native plant, and it is doing wonders for my Gatekeeper butterflies, but I introduced it into my garden from seed I collected in a local wood:

But many plants come of their own accord, and because gardens have such a mix of little microhabitats - turned soil, permanent 'grasslands', shady areas, sunny spots - this great bouquet of life can flourish.

There is one thing I need to be mindful of as I push for 600, and that is that wildlife needs mass as well as diversity. What I mean by that is that one Hemp-agrimony plant or one Wild Parsnip doesn't really cut the mustard for wildlife, just as one reed plant is no use to a Bittern or Reed Warbler. So lots of plants, and lots of each type, is the best mantra tofollow.

Keeping a record and totting up what plants you have has one other big benefit. It lures you into every corner of the garden, stimulates curiosity, and gets you even closer and more intimate with your garden and its incredible wildlife. You'll probably find things you never knew you had. So give it a go - get out there with a little note pad, and see if you have the diversity of a tropical rainforest.