Of all the tools I use in wildlife-friendly gardening, one of the most indispensible is a pack of little brown envelopes.

I always have some in the right-hand back pocket of my jeans, some in my camera bag, and some in the glove drawer in my car (how quaint, the idea that I should keep my gloves in there! Emergency chocolate bars and brown envelopes is all you'll find there, I'm afraid).

It is by means of the humble brown envelope that I have filled much of my garden with life, for in them I stash wildflower seeds when I chance upon them in the countryside.

The seed collecting season is a long one - some can be ready by late spring, and perhaps the key time is at the end of summer. But if you've yet to start, there are still plenty to be found right now in autumn.

So, this week I've been taking a break up in Norfolk, a chance to get some air in my lungs and miles in my legs with some long autumnal walks. All the while, there is a part of my brain that is ever on the look-out for some of these tiny brown nuggets that turn into pure gold.

At this time of year, spotting them can be almost an art in itself, as gone are the colour-filled attention grabbing flowers and instead the plants are often dried and wizened and, to be frank, on the ugly side.

So, for example, in one place I found extensive patches Broad-leaved Everlasting Pea.

Now this is a plant I want in my garden because it is the foodplant of the Long-tailed Blue butterfly, a real rarity but one which seems to be reaching our southern shores with ever increasing regularity.

So just one pod from the thousand or so that were on the plants will give me all I need:

Which leads us into the rules (and indeed laws) of collecting wildflower seed.

The legal situation is basically that, if a plant is genuinely growing in the wild, you are not allowed to uproot it but you are allowed to collect seed for personal use (not for commercial). However, there is an important caveat in that it can be illegal to collect seed from a SSSI (Site of Special Scientific Interest) or National or Local Nature Reserve. And of course you mustn't trespass to get it!

So that leaves a lot of what I'll call 'general countryside' where it is perfectly legal to pick seed, but where there is also some good practice to follow. The Wild Flower Society has a Code of Conduct, which also covers picking of the flowers themselves, but when your aim is seed collecting for home growing, the following are general rules to follow:

a) Only collect seeds where there is a large number of the species growing

b) Only take a few seeds. These four seeds I'm collecting from this Carline Thistle are plenty:

c) Don't trample other vegetation to get to your seeds

d) If in doubt, don't pick

e) And remember that a few seeds are toxic, so wash your hands afterwards.

Seed is best collected on a dry, still day, and then it is just a matter of looking for those plants where the seeds are ready.

So this week I was able to collect seeds of things such as this Hemp Agrimony (such a fine flower for nectaring butterflies):

In they go, into the magic brown envelope. Date, species and location written on the packet, and into my left-hand back pocket (ah, you see there was some method at work in having my empty envelopes in my right-hand back pocket).

And on to the next, which in this case is Meadowsweet, perfect for my new wetland area:

Once home, I tend to sow some of the seed immediately into pots outside, and keep some in the salad drawer in my fridge for sowing next spring.

All in all, there is so much pleasure in the searching, with the prospect of so much ultimate pleasure should they germinate and grow and attract wildlife aplenty to your garden. And all for the cost of a little pack of envelopes!