Frost Damage

To keep with the Halloween theme, here’s Arlena’s image of her succulent stuffed pumpkin.

There are a couple of pointers to remind me of the oncoming cooler weather. Two being the shorter days and the ever decreasing times that I can take my dogs for a walk in the daylight around the park. Then there’s the butter dish on the kitchen table. Gone are the days when I can scrape out big dollops of lovely creamy butter onto my knife. It’s now a case of placing lumps on the toast and letting it soften. We are slowly being acclimatised to the colder weather so when the first frost comes it’s not too much of a shock to the system. Plants also acclimatise themselves, not by putting the butter in the microwave, but by changing their metabolism, anatomy and physiology to prevent frost or chill damage.

How do plants cope?

One response plants have to dropping temperatures is the thickening of liquid within plant cell membranes, from a liquid to a gel-like state with amino acids. This slows everything down, conserves energy and lowers the freezing point, a bit like antifreeze. At the same time, the cell membranes themselves become more permeable, allowing water to leak between the cells as a kind of buffer. This is the process of cold acclimation.

Acclimatisation is also known as ‘superfreeze’ where the cell contents remain liquid even though below freezing point. To do this plants have to experience several days of cold weather before the freeze and this explains why even hardy plants can be damaged by a sudden autumn frost.

2 Types of Frost

The two main types of frost are advective or radiative, depending on the atmospheric conditions. An advective frost occurs when cold air sweeps in, usually with strong winds. A radiative frost occurs on clear nights where there is little or no wind.

  

Frost can Benefit Plants

Frost can actually benefit some plants. Deciduous fruit trees benefit from winter chilling, and cold snaps turn starches to sugar in crops such as parsnips, improving their flavour.

Frosts can also disrupt pest and disease cycles, and improve soil structure – when moisture within soil freezes, it expands, and splits open soil particles.

Prevention of damage

There are a number of ways to keep your plants safe during cold weather;

Choose plants that are reliably hardy and suited to your growing conditions. 

Select planting positions carefully to avoid ‘frost pockets’ this usually happens at the low point of the garden.

Slightly tender plants should be grown in a warm sunny spot, against a south-facing wall for example, which will provide some extra warmth and winter protection.

Cover plants with a double layer of horticultural fleece or other suitable protection when frost is forecast. This cover is thin enough to let sunlight in, warming the soil and to keep in the warmth at night as the temperature drops.

Mulch the root area of evergreens now, conifers, tender shrubs and tender perennials with a thick layer of organic matter to prevent the ground becoming frozen. This is better done in warmer weather as adding mulch later on could trap the cold air in the ground.

Move container-grown plants to a sheltered part of the garden in cold weather and provide some extra protection by wrapping the pot in bubble wrap.

Leave the previous seasons growth on more tender plants until spring, for example penstemon, as this provides valuable frost protection during the winter.

Tender plants can be lifted or moved to a more sheltered position or greenhouse. If this is not practical then protect them by wrapping them in sacking. 

Lift tender perennials such as dahlias, cannas, pelargoniums and fuchsias before the first frosts.

Hardiness can be improved by feeding plants high concentrations of soluble nutrients including potassium and sugars in the growing season. Some plants also have physical protection such as thick bark, furry leaves or a canopy that protects the inner shoots. Avoid applying nitrogen-rich fertilisers late in the season though as they stimulate soft, sappy growth which is especially vulnerable to frost damage.

Plants exposed to early morning sun may thaw too rapidly after a frost, causing damage to flowers and young growth. Camellia and magnolia flowers in particular can be ruined by a single frost.

Ensure tender plants are overwintered safely in the greenhouse by providing adequate heating or insulation

It's the late frosts that we should be the most wary of. Plants emerge gradually from dormancy in spring, but they can still respond quickly to sudden spikes in temperature which triggers new fresh growth which is very vulnerable to cold snaps. It’ll be a while before we need to give that any thought though!

Why Did My Plant Die?

Pumpkin Pictures

I can tell by the empty crates in the shops that a lot of us have bought pumpkins this year. I might be wrong but I’ll bet that most of us don’t take them into the kitchen and make good old pumpkin pies. I think most of them will be used to make a spooky faced doorway Halloween candle holder to scare the trick or treaters knocking at the door.

There are some really inventive carving ideas out there and you can even get special pumpkin carving tools if you are taking things very seriously.  Have you been creative this year? If so could you send me your images of the scary work of art, I can post the best ones on the Gardening Matters blog and maybe even put a really scary one here next week. Either send the images to me at info@gardening.ie  or directly to the Inishowen Indo via email, Tweets or Facebook. We look forward to being spooked!!

Back in the 1980’s, Geoffrey Charlesworth wrote a book called “The Opinionated Gardener,” In the book is a poem in answer to why a plant has died. I read it and had a bit of a chuckle to myself initially but then realized that intervening in the course of nature can be a tricky business. A self-set plant in the garden will grow quite happily, but when we get involved the list of things that could go wrong are long. I think Geoffrey has covered most of the answers as to why a plant dies when we try to grow it in his poem. Hopefully it won’t crush your self-confidence; I for one can tick off every one of the reasons as I have done them myself at one time, and still like to garden!

Why Did My Plant Die?

    Geoffrey B. Charlesworth

    You walked too close. You trod on it.

    You dropped a piece of sod on it.

    You hoed it down. You weeded it.

    You planted it the wrong way up.

    You grew it in a yogurt cup

    But you forgot to make a hole;

    The soggy compost took its toll.

    September storm. November drought.

    It heaved in March, the roots popped out.

    You watered it with herbicide.

    You scattered bonemeal far and wide.

    Attracting local omnivores,

    Who ate your plant and stayed for more.

    You left it baking in the sun

    While you departed at a run

    To find a spade, perhaps a trowel,

    Meanwhile the plant threw in the towel.

    You planted it with crown too high;

    The soil washed off, that explains why.

    Too high pH. It hated lime.

    Alas it needs a gentler clime.

    You left the root ball wrapped in plastic.

    You broke the roots. They’re not elastic.

    You walked too close. You trod on it.

    You dropped a piece of sod on it.

    You splashed the plant with mower oil.

    You should do something to your soil.

    Too rich. Too poor. Such wretched tilth.

    Your soil is clay. Your soil is filth.

    Your plant was eaten by a slug.

    The growing point contained a bug.

    These aphids are controlled by ants,

    Who milk the juice, it kills the plants.

    In early spring your garden’s mud.

    You walked around! That’s not much good.

    With heat and light you hurried it.

    You worried it. You buried it.

    The poor plant missed the mountain air:

    No heat, no summer muggs up there.

    You overfed it 10-10-10.

    Forgot to water it again.

    You hit it sharply with the hose.

    You used a can without a rose.

    Perhaps you sprinkled from above.

    You should have talked to it with love.

    The nursery mailed it without roots.

    You killed it with those gardening boots.

    You walked too close. You trod on it.

    You dropped a piece of sod on it.

Green Spuds

I don’t know about you but I find the cleaned spuds we buy from the shops go green really quicky, even stored in the cupboards away from light. It might be the fact that they are clean with all of the soil washed off, or it could be that they were ‘turning’ anyway before I got them. I don’t grow potatoes myself so have to look closely at the ones I do buy, which isn’t always easy when they are stored in brown paper sacks. 

Have you ever wondered how toxic green potatoes are? I don’t even eat the green crisps when I buy a packet so it’s been instilled into me never to eat the green bits. 

Green-Skinned Potatoes

Why do potatoes turn green? The green is chlorophyll, caused by the potatoes being exposed to light. Chlorophyll is not poisonous. But the same conditions that promote chlorophyll production also increase the formation of solanine, which is poisonous. So the green is an indicator of likely trouble, but is not trouble itself.

Potatoes can also have dangerously high levels of poisonous solanine without being green. This can happen if the potatoes are diseased or damaged, or they are stored in warm temperatures, or they experience a spring frost and make only stunted growth as a result.

Solanine is one of the potato plant’s natural defenses against diseases such as late blight, and against pest attacks.

Just discarding all green-skinned potatoes won’t remove all the solanine from our plates. Solanine is a glycoalkaloid found at some level in all nightshade crops. 

Apparently the amount of solanine in an average-sized serving of potatoes is easily broken down by the body so we don’t need to worry. Green skins contain 1500-2200 mg/kg total glycoalkaloids though which can be poisonous.

The British Medical Journal of 8 December 1979 reports that there is normally a high concentration-gradient between the peel and the flesh, but this is lost when potatoes are exposed to light or stored in adverse conditions. This means the level of solanine quickly drops as you peel deeper into the potato, unless the potatoes were exposed to light or were stored in a warm place for several weeks or more.

Green Potato Myths, Dispelled

The Department of Animal Science at Cornell University says that solanum-type glycoalkaloids are not destroyed by cooking. There isn’t any real evidence to say it increase arthritis conditions either.

“Solanine is water-soluble, so boiling lowers the levels.” An infamous 1979 case of 78 London school children getting very sick after eating boiled potatoes that had been stored improperly over the summer vacation seems to prove this belief not true. (All made a full recovery.)

The US National Institutes of Health advises never to eat potatoes that are green under the skin. This is ambiguous and has been interpreted to mean either: throw out all potatoes with any green bits, or cut off the green skin and also any green flesh under the skin and eat the rest of the potato. Most of us  seem to cut off the green bits and use the rest.

10 Steps to Safe and Healthy Potato Eating

1. If you do grow potatoes, try to cover them fully with soil or mulch, so that they are not exposed to light.

2. Give plants enough space so that the developing potatoes are not crowded and pushed up above the soil surface.

3. If mowing to reduce weeds before mechanical harvest, keep the length of time between mowing and harvest to a minimum. For the same reason, harvest soon after removing mulch. Hand digging can be done without removing weeds or mulch first, but there is a limit on how much one person can hand-harvest.

4. When harvesting, minimize damage to the tubers.

5. When sorting potatoes for storage, do not put all the ones showing any green in the same container. Leave the green-skinned potatoes mixed with the others, so that no-one gets a higher amount than average.

6. When storing potatoes, keep them in the dark, and cool. Don’t store them for longer than necessary. There seems no need to worry about storage up to one year or so, as generations of potato growers have provided for their family needs this way.

7. Apparently there is no reason to use green potatoes sooner than others. Nor is there apparently any advantage to storing them longer in the hope of de-toxifying them.

8. When preparing potatoes for eating, cut off and compost the green bits. Don’t use all the greened potatoes in the same meal. Reduce the risk by mixing greened and plenty of non-greened potatoes.

9. When eating, spit out any potato that tastes bitter.

10. Enjoy eating your potatoes fried, boiled, mashed, chipped, baked or roasted.