The tell-tale signs of autumn are beginning to appear in the woody perennials. Being larger, the trees have the biggest impact when fully coloured up, but many shrubs will also contributing a stunning show both with leaf colour and various fruits. Some herbaceous also get in on the act.
What causes leaves to change colour at this time of year? Both the internal clock of plants and the weather have a role to play. Some plants always turn colour around the same time each year. Horse chestnut and birches are some of the first, normally in early to mid-September. Others such as maples follow according to their internal timing or the weather.
New England in the northeast USA is famed for its autumn display. The ‘fall’ weather there is reliably warm in the daytime and quite cold at nights, affected by the adjoining landmass of Canada. Ours is a more maritime climate. The sea tempers some of these extremes, but on years when we see the whole canopy aglow with oranges, reds, and yellows you are also likely to experience that same weather experienced in New England.
Those colours haven’t just developed recently. They’ve been there all along but are masked by the green pigment found in the leaves’ chlorophyll. It plays a big part in photosynthesis, the process whereby leaves turn the sun’s energy into plant food/sugars.
The leaves are responding to the signals of temperature and day length. The message is that cold weather is coming, too cold for all those enzymes in the plants to work in promoting growth. The plants’ strategy is to now lay-up stores for the cold weather and ditch their leaves, which will soon become a liability.
Plants are the ultimate recyclers, and if resources have been used to make chlorophyll which is no longer needed, those chemicals will be transported and used somewhere else in the plant. The sugars made by photosynthesis will be converted to starch and stored in both stems and underground storage organs.
This process is called ‘translocation’ (‘trans’ meaning ‘across’, and ‘location’ meaning ‘to a different place’). You will have seen this process already, and it is gearing up rapidly as the temperatures start to fall.
Translocation is also the way plants store food to keep them alive in hard times. We often see shrubs’ lower leaves go yellow before they drop, especially when dry (pictured). The nutrients and the chemicals within chlorophyll have all been moved out to the growing tip of the stem. Well-watered plants don’t often show this yellowing.
When tattie haulms go yellow, the chlorophyll has broken down and all those nutrients have been passed down the stem to the tubers (the tatties) under the ground. Those sugars that were made in the leaves are now stored as starch.
Why does the plant do this? All those leaves and stems containing the food from the sun as sugars are going to be frosted soon. So like a squirrel storing acorns in order to have a food supply in hard times, the plants do the same and move those sugars to a place of safe storage. The resources used in making sugars are not wasted now the plant has its food store safely underground. Starch stores well, better than sugar which dissolves easily.
If you collected seed earlier on, it will need cleaning. This is a job which can take place anytime in the next few months as long as the seeds are kept as dry as possible. But if you can, do it sooner. Some larger seeds, like nasturtiums (‘Tom Thumbs’) may need no attention.
The idea is to remove anything that isn’t a seed from the contents of your envelope, whether that is the protective capsules/pods the seeds developed in, leaves, stems, or general vegetable rubbish. Any of these things can carry fungal spores which can infect the seeds.
The process takes time but the end product is very satisfying. Seeds are so different from species to species so how you clean them is up to you—see what works best.
For many, tip them out onto a slightly rough sheet of paper, hold it at a slight angle and tap gently so that seeds roll off onto a tray below. Some of the dross will stick to the paper so you can wipe this away with your finger. You may need to repeat this several times but eventually you will have just seeds left. Seal them into a paper envelope and label them.
Blowing gently across the seeds and dross may remove lots of extra material. Be careful that the seeds don’t also disappear. In some varieties there may be some that are very light and small compared to the rest of the seeds, and these light seeds may not have enough stores within the seed coat to make the seed viable. Let them go and save the more substantial ones.
Others may be within a hard capsule which needs cracking to release the seeds. Use pliers or a hammer, doing it within a paper bag will stop the seeds flying everywhere when the capsule cracks. Then clean away the covering material.
Fruits and berries are colouring up now. In a year like this one, where night temperatures are still warm, the leaves may fall without providing much of a show, but at least the berries provide a real splash of colour.
Choosing the best plants, harvest some fruits and bring them in to protect them from birds and mice. They don’t need frost protection. Lay them out so they don’t go mouldy. Label.
You can process them on a wet day, which involves picking the fruit apart, removing the healthy-looking seed, and then washing off any goo from the berries. A sieve is good for this job. The goo contains germination inhibitors, which may slow the seeds down from germinating for a year or more. Dry off the seed and store it in a cool place.
I like to harvest rowan and elderberry heads, put them into a carrier bag and stick it into the freezer. When I open the bag, at the lightest of touches the berries fall off their stalks. The birds really appreciate them during snowy periods.
There is still time to take semi-ripe cuttings from shrubs. The base should be slightly woody and the growing tip will be slowing down as far as growth—still green but not soft. Cut them off above a bud on the shrub, a longer length than you need for the finished cutting. Trim the cutting below a node and remove all but the top one or two twirls of leaves, a length of 10 – 15cm is average.
Insert them into a mix which holds moisture, drains well, but gives a little nutrient. We’re using fine leaf mould and vermiculite. You could use bagged compost instead of leaf mould, 50:50 with vermiculite. Cover with clean polythene.
This year I have been trying shorter cuttings within a fruit punnet, a plastic box with holes for drainage and air. Keep it out of the sun. So far, most have rooted.
Other jobs include bulb planting and removing the massive weeds that escaped your notice at the last weeding. By removing all the other weeds at the last weeding, you have removed their competition, so they grow big and produce double-huge numbers of seeds. Zap them to save work next year(s). I don’t compost them as our heaps may or may not get hot enough to kill the seeds. Feed them to the voles.
We’ve removed our bird feeders temporarily, but I confess to providing a few seeds to the vole that once made a living below where they hung. We call him/her ‘Moose’, owing to misidentification at the start but it hasn’t complained.