Ensure that tall plants and especially large flowered dahlias, are well staked, as late summer gales are common in August. Even without winds, the weight of the flowers can snap the stems, especially when wet with rain.
Earwigs can prove to be a nuisance in August, especially amongst the dahlias, as they eat the young shoots and leaves at night and may even attack other plants such as delphinium and asters. A traditional method of trapping them is to place a flower pot, filled with straw or grass, upside down on top of a stake near the plants at risk. The earwigs will collect inside the pot, as they hide from the light. Simply remove the pot each morning and dispose of the contents. Then refill with straw or grass and set the trap again for the next evening.
Sow butterfly flower (Schizanthus) and stocks now to give a green house display next spring.
Madonna lilies (Lilium candidum) can be planted this month. It seems an odd time of year to do so, but these lilies begin growing new roots and leaves from late August. Choose a sunny spot and well drained soil. Plant them shallowly under 5cm (2 in) of soil, also add a little lime to the surrounding soil.
If you haven't started your tender cyclamen into growth, do so now.
The rhizomes of arum lily (Zantedeschia aethiopica), can be started off this month, either from newly bought plants, or existing plants that you have been resting through the summer. They need large pots of about 25 cm (10 in) using a soil-based compost. Keep the compost on the dry side until signs of growth appear, then increase watering.
Early flowering tuberous rooted begonias and hippeastrum (Amaryllis) bulbs should now be gradually dried off ready for storage.
Pelargonium cuttings can be taken now, so they can be well rooted by the time the cold weather comes. Follow the same method as for cuttings taken in spring. If your pelargoniums are good sized, you should be able to take plenty of cuttings without disfiguring the plants. The plants will respond to this pruning by sending out fresh side-shoots. For details see our section on Propagation by Cuttings.
Keep cutting sweet peas, to fill your house with scent and to keep the flowers coming on the plants.
Start cutting everlasting flowers for drying now. Besides the ever popular honesty (Lunaria annua) and straw flower (Helichrysum), try drying the lovely green bell-like calyces of Ireland (Molucella laevis). If you haven't grown special flowers for drying, try experimenting with what you do have. Hydrangeas dry very well, for example, and you can try drying ferns, flowers belonging to the daisy family, and ornamental grasses.
The flowers or foliage you intend to preserve must be bone dry and in peak condition to start with. Hang them upside down, either singly or in bunches, in a dark, airy place. Do not make the bunches too big, or the air won't be able to circulate freely.
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Herbaceous perennials in flower this month:
Achillea (Yarrow or Molfoil)
Alstroemeria (Peruvian Lily)
Aster (Michaelmas daisy)
Campanula (bell flowers)
Hemerocallis (day lily)
Hosta (plantain lily)
Kniphofia (red hot poker)
Tradescantia virginiana (spiderwort)