The Flower Garden in Late Summer
What to do in the flower garden in September
September is an important month for bulbs, corms and tubers. It is time to attending to bulbs which have just flowered, plant spring flowering subjects outdoors, plus plant bulbs that are to flower indoors, in bowls, during the winter.
Lifting and Storing Half-hardy Bulbs
Unless you live in a very mild area of the UK, it is better not to leave half-hardy bulbs such as gladioli, freesias and dahlias in the ground during the winter. If they are not killed by the cold weather, then slugs or mice will probably get to them.
Once the foliage has half-yellowed, dig them up carefully, label them by variety and description and cut the tops back to about 1 in (2.5 cm). Don't leave the tops on to die down completely as this invites diseases.
Dry corms under cover, clean them by removing the old roots and any bulbils (which can be grown on) and store them in a frost-free place until the spring.
Planting Spring Flowering Bulbs
Bulbs for flowering outdoors next spring can be planted out at any time from September, up until as late as November. There are many ways and places to position spring flowering bulbs outdoors. Formal bedding is certainly the most spectacular place to grow bulbs, but not all spring bulbs are suitable. For example, daffodils and other narcissi have a great deal of foliage, and finish flowering well before it is time to plant the summer bedding.
Pride of place for a low-growing display must go to the hyacinths. They are perfect for growing in tubs or window boxes. Many of the early flowering tulips are also excellent, but it is the May flowering tulips that really make an impact in the borders and mix well other spring flowering bedding plants, such as wallflowers.
Even if you don't have a large garden, bulbs can be grown in tubs, troughs, window boxes, hanging baskets or virtually anywhere there is space.
Daffodils and narcissi are ideal candidates for naturalizing along with aconites, snowdrops and snowflakes (leucojum), including crocuses if the position is sunny. It is best to grow naturalized bulbs in bold groups so that they really make an impact.
To naturalize bulbs in the lawn use a special bulb planter or trowel to lift a core of turf and soil. The bulb is then dropped in the hole and the core replaced (after removing a portion from the bottom of the core to allow enough space for the bulb).
Rock gardens are another ideal area where small bulbs can be naturalized. Some of the more popular bulbs for the rock garden are: aconites, anemone, chionodoxa, crocus, cyclamen, miniature irises, miniature narcissi and grape hyacinths.
Soil preparation is minimal, except that the drainage must be good, which can always be improved by putting some coarse sand or horticultural grit in the holes before planting . After planting bulbs in a mixed border, always mark their position with sticks or markers so that you don't dig them later by mistake.
In order to force bulbs in bowls for flowering indoors during the winter, you don't need a greenhouse, but you do have to do the right thing at the right time. The earliest to flower are the 'prepared' bulbs, the most popular of which are hyacinths, which have been specially treated by the grower so that they will flower much earlier than normal. These can be planted by the middle of the month in bowls of good quality bulb fibre. However, because the bowls need to be plunged outdoors for a couple of months, it is often better and safer to start them off in deep trays or biodegradable pots so they can be planted directly into the bowls when ready.
After planting, keep the bulbs as cool as possible for eight to nine weeks. This is best done by plunging them in a bed of moist compost or ground bark in the coolest part of the garden. This treatment is essential if the flower buds are to form properly. If the flowers come out small and highly coloured, it means they weren't kept cool enough, for long enough. When the tops have grown about 1 in (2.5 cm) usually towards the end of November, bring them into gentle heat indoors. Unprepared bulbs of hyacinths, daffodils, narcissi, and first early tulips can be grown in just the same way, except they need a fortnight or so longer outside and will, in consequence, flower a little later.
Deadheading and Weeding
Carry on deadheading where necessary. Any hardy annuals that have finished flowering and which are dying should be pulled up and composted. Keep hoeing so that no late-season weeds run to seed.
The need for pest and disease control should be much reduced by now but you should still keep your eyes open for any late burst of fungus diseases.
What Flower Seeds to Sow in September
Any hardy annuals that were not sown last month should go in now, or they will be unlikely to make large enough plants to withstand a hard winter.
You can still get good results from taking semi-ripe cuttings of hardy shrubs. As with seedlings, you should not take them too late or they will be difficult to over winter, unless they can be kept under cover. For details see Propagating Plants from Cutting.
Flag irises can be lifted and divided straight after flowering, early in the summer as long as they are kept well watered to enable them to send out new roots. However, in the drier eastern parts of the UK, it is usually wiser to wait until September as rooting and subsequent growth will be more certain. Lift the clumps, split them up so that only the most recently grown section of rhizome is retained and replanted. It is normal to cut the leaves back into a fan shape some 15 cm (6 in) long to reduce water loss. Plant firmly, with the top of the rhizome just showing above the soil.
Iris stylosa can also be planted or divided now.
Looking after Plants in Containers
Containers will still need close attention to keep them in good condition at this time of year. Deadhead plants in hanging baskets, tubs and other containers regularly and often to keep them flowering and check regularly to see if they need watering. Feeding can usually be reduced to once a fortnight by the end of the month because growth is slowing down.
Plants for September
Herbaceous perennials in flower this month:
Acanthus (bear breeches)
Alstroemeria (Peruvian Lily)
Aster (Michaelmas daisy)
Hemerocallis (day lily)
Kniphofia (red hot poker)
Solidago (golden rod)
For bulbs see