Your Garden in September
We all have parts of the garden that have passed their peak and need rejuvenation. This does not mean ripping everything out and starting again but perhaps replacing plants which have become tired and past their best or are in the wrong place and need moving. This can be done at any time but autumn is the very best time to start. It is an ideal time to replant while the soil is still warm and roots will get established. Perennials that flower early in the season can be divided up if they become overgrown and congested. Those that flower later in the year need to be divided in the spring. If any herbaceous plant has given up the ghost or its centre has become woody it is probably time to say goodbye as dividing up may not save it. Any plant that may have turned out to be a thug and has taken over may need removing altogether and replanting with something that is better behaved.
If you do need to move a shrub that is perhaps in the wrong place, it is worth preparing it now for the move. It may need pruning back to give a well balanced shape and open centre. With mature shrubs it is also an idea to prune the roots by slicing through with a sharp spade making a trench around the plant. This will encourage the plant to make new feeding roots and make the move less traumatic. Prepare the new site by adding plenty of organic matter and making the hole wider than the rootball.
Autumn is a good time to divide plants that flower early in the year, late flowering perennials such as asters and rudbeckias should be tackled in the spring. Some plants can be pulled apart by hand or dense roots and solid crowns like hostas can be chopped into chunks with a spade.
Lawns will need help to recover from the summer stress. Start by mowing, then scarify the surface with a wire rake, removing any dead material and moss. Improve drainage and relieve compaction by
making holes with a fork or hollow tined aeration tool. Finally apply a top dressing, which you can buy ready-made or mix your own using compost, loam and fine grit. Spread the top dressing thinly and evenly over the lawn so that it smooths over any dips and falls into the holes.
We use the term ‘bulbs’ quite loosely to cover true bulbs, corms, tubers and rhizomes. They are all food storage organs, but a true bulb is a condensed shoot with leaves, stem and flower compressed into a neat package. A corm such as crocus is a condensed stem with an embryonic flower sitting on the top and a tuber may be either a fleshy stem with buds all over (as in a potato) or a fleshy root with buds at the top (as in a dahlia or tuberous begonia). Rhizomes (such as irises) are horizontally growing fattened stems (usually just below the soil level) which send out both roots and shoots. Depending on the type of plant they will provide colour throughout the year. Spring flowering bulbs should be planted as soon as possible (apart from tulips which are best planted in November) The rule of thumb with most bulbs is that they should be planted in a hole that is three times the depth of the bulb itself. If planted too close to the surface the bulbs can dry out and fail to flower in later years. It is better to plant deeper than too shallow. When planting bulbs in containers use a mixture of multi-purpose compost, John Innes and horticultural grit planting closer together than you would in the open ground.
Some other jobs to do in September
Stake kale and brussels sprout plants to prevent wind rock damage occurring later in the year.
Now that the light levels are decreasing remove shading from the greenhouse and clean the glass, keep the vents open on warm days.
Prolong the flowering period of perennials such as asters, heleniums, salvias and dahlias by regularly dead heading. Keep cutting sweet peas and dead heading roses.
Give hedges a final trim
Trim lavender, cutting back to just within the leaf growth above the woody stems and never below.