Gardens: cut and thrust

We inherited a very pleasing white hydrangea when we moved to our new garden. It was growing on a steep, south-facing slope in the shade of a large willow. I thought the position might be rather too thin and dry for a shrub that likes plenty to eat and drink, but it continues to grow lustily and is now 6ft wide and 5ft high. The flowers are the lacecap type, with big sterile florets ranged round a centre of small knobbles, all greeny- white at first, but developing into pure white heads that gleam in the shade.

This patch, being very steep, is not an easy place to garden. It's close to the boundary and is regularly re-infested with ground elder, Japanese knotweed, marestail and other nasties that crawl in from beyond. But we look down on it from the lawn above. It needs to provide a view worth having. I'm hoping that if we jam-pack the slope with shrubs that can live with an underlay of ground elder, we'll have something decent to look at without creating too much extra labour.

The hydrangea had evidently been coping very well with the competition and I thought we'd have more. But what was it? Looking at Hydrangeas by Toni Lawson-Hall and Brian Rothera, 'White Wave' seemed the closest match, but there the centre of the flowerhead is described as pale pink, opening to blue. Ours is all white. The only way to be sure of getting more of what we wanted was to take cuttings.

We did that last winter, taking hardwood cuttings, about 20-30cm long, from ripened stems of that year's growth. By November this had become quite firm and strong. Hardwood cuttings can be stuck into any spare bit of sheltered ground with two-thirds of the stem buried, but they must go in the right way up. If you make a straight cut at the bottom of the cutting and a sloping one at the top, you'll be reminded of what you have to do. Then all you need is time, because this is the slowest method of propagating plants – a year before you can hope to dig them up and shift them to their permanent homes.

Unfortunately, our hardwood cuttings show no sign of life at all and I'm not convinced that deep underground, anything is happening. So, as a back-up, we've taken some semi-ripe cuttings this month (you can do it any time between July and September) and hope for more immediate signs of success. A semi-ripe cutting is just what it says – halfway between the soft, leafy growth you use for a softwood cutting and the mature growth you take for a hardwood cutting.

On a hydrangea, you are likely to find the kind of non-flowering wood you need around the edges of the bush. Look for growth that is still soft and leafy at the top, but faintly woody at the base. The cutting should be somewhere between 10-15cm long. You are often told to take semi-ripe cuttings with a "heel", the name for the bit of old wood that comes away with the side shoot when you give it a sharp downward tug. Semi-ripe hydrangea cuttings tend not to have heels. They break off cleanly where they join the older stem. Trim the cuttings to a point just below a pair of leaves, strip off those leaves entirely and cut the rest of the leaves in half (you only need to do this with big leaves such as the hydrangea's).

Take out the growing tip of each cutting and stick them round the edge of a pot of compost lightened with sand or Perlite (you can get four cuttings into an 11cm pot). Water the compost and then cover the cuttings with a polythene bag, puffed up over their heads and held in place with a rubber band. Keep the pot on a windowsill that is well lit, but not in direct sun. A propagator is not essential but will speed things up by providing heat under the bottom of the pot.

Watch for new growth springing from the cuttings. That's a reasonably hopeful sign that they've rooted. Then you can gently tease them apart to continue their lives in individual pots. Buddleia, evergreen ceanothus, chaenomeles, choisya, many conifers, escallonia and hibiscus can all be propagated now from semi-ripe cuttings. So can actinidia (kiwi fruit), albizia, arbutus, berberidopsis (coral plant), callistemon (bottle brush), carpenteria, corokia (wire netting bush) and plenty of other shrubs that don't have the advantage of being at the beginning of our alphabet.

Now is also a good time to sow seed of hardy annuals such as ammi, the quaking grass (Briza maxima), English marigolds, cornflowers, cerinthe, Californian poppy, orlaya (the prettiest annual in our garden this year), love-in-a-mist, Shirley poppy and opium poppy. On the light ground that we've now got, I've become very casual about seed of Californian poppy, opium poppy and love-in-a-mist, and simply sprinkle it straight on the ground that I want to cover. These annuals are particularly useful for following on from early crocus and species tulips. The bulbs are all top-dressed with 6mm grit and the seeds seem to cope with that very well.

Without doubt, the best of the three different love-in-a-mists in the garden this year has been Nigella hispanica which has bigger, darker flowers than Nigella damascena. The centre is much more extravagant, a big dark column with eight or 10 strong horns that become even more pronounced on the vase-shaped seedhead. It is a great beauty. Autumn-sown annuals come into flower earlier than spring-sown ones; for the longest possible season, make a further sowing in April next year.

Because I'm not so familiar with their ways, I treat ammi and orlaya differently, and will sow seed in a 12cm pot at the end of this month. It germinates fast and later, and you can prick out the seedlings into individual pots which gives superb plants to put out next spring.

This year, the orlaya flowered first followed by the ammi which was still going strong at the end of July. Another sowing in late spring would give plants the chance to continue through August. So although late August may seem like the beginning of the end of the gardening year, it can actually become the start of an entirely new one.