Disbudding Cuttings Improves Growth

You will often hear it said that it pays to remove buds from cuttings because they take up energy which could otherwise be used for growth. Whilst this is undoubtedly true, it is not my main reason for dis-budding.

Once a cutting starts to form flowers (and most of them do, surprisingly early) it stops producing new stem and leaves. This is a problem for me, since the growing season is already too short (apart from insurance, this is why I take cuttings for next year's plants - to give them a longer season). I like the plants to get some growth over the winter months, albeit apparently somewhat stunted; this will give them a really good start next season.

Take care when removing the buds, not to disturb any delicate new roots which might have formed.

Should We Keep Pots Wet or Dry in Winter?

This is the $64k question. It's a situation where growing suddenly becomes an art: where something which sounds easy to work out on paper suddenly becomes incredibly complex.

Just in case you don't want to follow the story (and who can blame you?), here's my advice: KEEP THEM AS DRY AS YOU CAN (i.e. don't water them unless you really have to). If you are unsure, stick in a thermometer and check things out.

CONDUCTION, CONVECTION AND RADIATION
We are back to conduction, convection and radiation again - with something called HEAT CAPACITY thrown in for good measure.

Heat Capacity
This is the amount of heat required to raise the temperature of an object by a given amount. Both water and bricks have high heat capacities. This means they are slow to warm up (think of coming home to find the heating has been off for a few days and how much heat it takes to get back to normal). Whilst this isn't good when planting in spring, it is fantastic in winter, since it means pots of wet soil/compost kept close to the house are much slower to freeze than they would otherwise be (think of standing next to a storage heater). So we just water pots and keep them close to the house? If only it were that simple.

WET COMPOST PRODUCES TURGID CELLS
Much depends upon whether the frost is severe enough - either through a large drop in temperature, or through the length of exposure during a prolonged cold spell - to cause the compost to freeze solid. Should this be the case, we can be in trouble. We saw recently that plant cells are damaged by the formation of ice crystals within turgid (full of fluid) cells, since the sudden expansion can rupture the cell walls. This is the problem with watering the compost; there is no way to prevent this water entering the plant and producing these turgid cells.

DRY COMPOST PRODUCES FLACCID CELLS
However, the flaccid cells produced in drier compost not only have more concentrated sap (which freezes at a lower temperature), but can also accommodate any ice crystals which do manage to form. This seems like a better situation. But things are complicated by the fact that plants, even in damp compost, can produce this situation by hardening themselves, as we saw elsewhere.

CONDUCTION AND CONVECTION
Sandy soils can be a problem for two reasons:
They are good heat conductors, so easily bring heat to the surface from down below.
They have large pores through which air currents can easily pass and remove heat by convection.

These soils tend to be too hot in summer and too cold in winter. The problem is made worse by the fact they cannot hold much water.

RADIATION
Lighter soils tend to be cooler, since they reflect the sun's heat back in summer and are reluctant to reflect valuable soil heat in winter. These effects are lessened if the soil is wetted, since it inevitably becomes darker and therefore a better radiator.

EFFECT OF MULCHING
Mulching can provide a solution. I like to apply dry peat or potting compost to pots and delicate plants just before a severe frost. This provides an insulating layer and helps considerably. Garden compost has a similar effect. If applied at this time, the lighter frosts will have had a chance to kill off some of the pests which might be in the surface layers. If using potting compost, take care not to use it around lime-hating plants (calcifuges).

How Plants Lose Heat

The best way to protect plants against frost is to understand how they can lose heat (note that they lose heat, not gain cold), then take appropriate action. There are three main ways:

Convection
Conduction
Radiation
Evaporation


CONVECTION
Associated with air currents moving around the plant and soil (think of putting on a jacket to keep out the wind). Most plants (and objects) have a layer of still air close to their surface, which acts as insulation. Air currents remove this. Some plants have leaf hairs, which help matters since they help trap this layer of air. Although the main function of this is to cut down water loss, it also helps insulate the plant. (and if the hairs are light in colour, they also aid cooling by reflecting back the sun's rays).

CONDUCTION
Associated with heat loss through making contact with a surface with a different temperature (think of touching cold metal with a warm hand). Since the ground is invariably warmer than the air on a frosty night, this usually warms the plant.

RADIATION
Even bodies in a vacuum can gain and lose heat by radiation, provided the sides of the vessel are clear; no air or contact is necessary. Dark objects are the best (or worst) radiators; light ones vice verse. As recently mentioned, fleece (because it is white) cuts down radiant heat loss (by reflecting back any heat trying to escape this way). We also saw in the summer that black pots could cause compost temperature to rise so much that roots could literally boil. Covering the pot with shiny aluminium foil helped prevent this and reduced temperatures considerably in the tomato pots. Foil will work the other way in winter.

EVAPORATION
Plants cool themselves in summer by 'perspiring' water through the pores (stomata) in their leaves. The act of turning water at 100 deg C to vapour at 100 deg C uses up much energy and takes this as heat from the plant, thus cooling it. The heat needed to do this is called 'latent heat of vaporisation'. The process of plant water loss is called 'transpiration'.

Water acts in the opposite way at freezing point, when it turns from liquid to ice - it GIVES UP HEAT to the plant surface and thus lowers the freezing point slightly, often just enough to prevent damage. Market gardeners spray their crops before nightfall when spring frosts are forecast.

The Worst of All Frosts

In the UK, a bitter east wind (forecast for later in the week) provides the worst of all frosts - a penetrating one. It might take more than horticultural fleece to protect sensitive plants.

Fleece insulates plants by preventing radiant heat loss and to some extent restricting air movement around them. But I don't think it will be strong enough to protect against strong air movements; these will brush aside the still air (because it's porous) and allow freezing temperatures to reach the plant surface.

Much protection can therefore be obtained by blocking up cracks in doors and windows through which this wind can pass. I am also going to cover plants with newspaper overnight to help reduce air movement around them. Fortunately, daytime temperatures should remain above freezing.

Don't Paint It Green

If you're thinking of giving your growing area a bit of a face lift some time soon, can I give you some advice: Don't paint it green. As you can see from this approximation of the absorption spectrum of chlorophyll 'a' (it shows how much of each colour the plant can use), plants use hardly any green light, tending to use light from the blue and red ends of the spectrum for photosynthesis.

I remember thinking it such a good idea to paint my rear porch green, only to discover much later this was why the plants weren't prospering - not the poor season which subsequently followed. It never occurred to me that plants are not really green: they only appear green because the chlorophyll (and other pigments) has absorbed all the other colours from the visible spectrum, leaving just the green light (or whatever an object appears to be) to be reflected to our eyes.

I find white the best colour for a growing room, especially this time of year when plants benefit from as much reflected light as possible. You can even use tin foil in the winter, though it tends to be too much when the sun gets stronger. Like we humans, plants can also suffer sunburn.

Coming or Going? Short of Phytoalexins?

With the shortening days and weakening light of late autumn, plants want to shut shut down and have a good long sleep till spring. Then they can awake refreshed about early February when things are picking up. Just like us, as tiredness sets in and they become weaker they are extremely susceptible to disease, since they have no vigour with which to resist it. Resist it? How do they do that?

Whereas humans produce antibodies with which to attack disease, plants have other methods:

• Firstly, they can restrict entry by quickly forming calluses (the plants' equivalent of scabs) over wounds.
• Secondly, they can produce toxins; woody plants, for example, often produce resins, which act as poisons. However, they can also react more actively.
  

ACTIVE DEFENCE
In the 1940s, scientists discovered that infected plants could react actively in response to fungal attack by producing substances which they called 'Phytoalexins'. Since that time about twenty phytoalexins have been discovered, of which each plant species uses one or two. Unlike antibodies, they are not species specific, so just like a contact fungicide they can be used against a wide range of fungal infections.

Now back to the fuchsias. It is hard to know whether the suddenly-yellowing leaves are caused by the plants trying to shut down, or whether it is our old friend botrytis gaining the upper hand as the plants lose vigour. Just a couple of weeks ago I noted how the healthy fuchsias grown in soil outside had resisted this disease. Could this be evidence of phytoalexin use by fuchsias?

Checking the Drainage

As you know, I have now lifted and stored some of the dahlias. But I usually leave some in the ground all winter. They seem to survive very well like this, especially if planted deep (at least 10 cm) and get some sun during the day. The sun thaws out any frost and prevents it penetrating deep into the soil during any weeks of continuous 24 hour bouts of freezing temperatures, usually in late December-early February when days are shortest. If storage is a problem, you can do this as well, with one proviso: the soil must not become water-logged.

What causes water logging? - Poor drainage.

How do you know if you have it? Dig a narrow hole about a spade deep and watch it. If it doesn't drain within about 8 to 10 hours after a bout of heavy rain, then drainage is a problem. If it doesn't rain, tip in a bucket of water. (Incidentally, if it drains too quickly, this indicates another problem - too-light soil (remedy by adding clay or compost)).

FACTORS CAUSING POOR DRAINAGE

High Water Table
As winter approaches, the water table gradually rises and can even reach the surface causing bogginess, even permanent puddles of wataer. This problem usually occurs with low-lying land; it does not affect most gardens since it is low enough beneath the surface. However, if you have this problem, you should think about a drainage system. Unless you do this, your plants will never do well (unless, of course, they are bog plants).

Heavy Soil
Heavy soils, such as clay, do not drain fast enough in times of continual rain. Dahlia roots (and also those of many other plants, especially bulbs and corms) do not like this and will quickly rot. Planting in sand will help to keep the cold wet earth away; it will also improve drainage by keeping the soil open. Adding compost, sand, or horticultural grit will help to improve the drainage.

Hard-Pan
If you live in a new property (or an older one), the garden might have been created by dumping topsoil onto what was effectively a building site compacted by heavy traffic. As the surface water seeps down, it is prevented from getting away by this layer and thus creates a false water table.

Hard-Pan can be cured by penetrating the pan, the more places the better. Although double-digging is best, just loosening the soil in spots close to each other will have a large effect. If you do double-dig, try to avoid mixing the subsoil (usually the lighter soil) with the topsoil (the darker soil), since it is invariably infertile. After removing the first spadeful, try to loosen the lower layer without lifting it out; this will allow the water to get through.

Patience Produces Short-Jointed Geraniums

Look how much shorter-jointed (shorter internodes) the geranium on the left is, compared to its partner: the larger cutting (which received normal feeding) we took in late summer. Furthermore, look how many axillary buds are developing into new shoots.

What's that: 'So what, you're not impressed'?

Well, think of it this way: Each new shoot will bear a flower. So the more shoots we have . . ..

Of course, this does't happen overnight; it takes time - too much time for most growers. But you might remember me telling you earlier that patience is a virtue when growing plants. Growing this plant slowly in almost dry soil (you can use compost - preferably seed and cutting compost, since it contains less food) with little or no feed is the proof of the pudding.

It's that hard growing again. And in my experience, this will reward you time and time again. Both plants are good cuttings. They will both make good plants. But I fancy the hard-grown one. Let's wait and see . . ..

I Should Have Node

This winter twig should demonstrate what is meant by nodes and internodes, at least as far as plants are concerned.

Axillary buds (those between the stem and leaf base) become dormant after leaf fall (as demonstrated here). So technically I should have labelled it 'dormant bud'. These are the buds we cut back to when pruning, the problem in older wood being they can be almost impossible to detect. Many's the time I have cut back an old woody stem only to discover buds developing in the most unexpected places.

As far as we growers are concerned, the internodes are important, since long ones develop into straggly plants. Light and temperature are key factors in this.