Tuesday, June 13, 2017

Gardening with Frost:

Tips and Tricks
Creating a frost-wise garden is more than choosing the right plants.

1. Map your garden’s frost shelters in winter. (See article below) Even the coldest garden has places where the frost doesn’t form. A tiny frost-free niche is all a plant needs, to get started. You may find, with careful winter research, that your frost-free areas are really quite generous in size.

2.  Plan your spring plantings, based on making best use of existing frost shelters. You may save yourself a lot of work and cost, for an equally satisfying result, by making some small changes in just where you will put your first gardens.

3. Grow frost barriers. Get started on a frosty site by putting in tougher plants, and arrange them so that in the future they will create new areas of frost shelter. Consider creating quick canopy - even low shrubs may be enough to give you a site where trees can safely start their lives. Also consider how you can plant barriers to divert the downhill flow of frosty air away from your future planting sites. (Always consider where the diverted frost flow will end up, though.) With good planning, you will notice how your area of frost-free garden space grows every year.
(Note that temporary fences of shade-cloth can also operate as frost barriers. They are not as effective as plants, but may be just what you need.)

4. Plant as early in spring as possible, to get maximum growth happening before the next winter. Use whatever watering techniques are available, to get the plants well under way before the summer heat. Remember that intelligent use of water - using water crystals, getting the water down deep without wasting any on the top layer of soil - will produce quicker growth than merely throwing lots of water at the problem.

5. Don’t waste tree stumps.
Some plants which would die if planted at ground level can thrive if placed a metre or more off the ground in a stump. Both its height, and its insulation are helpful factors. Ficus rubiginosa (of local provenance) is a good, tough species to grow this way, and will make a big, bird-attracting, frost sheltering canopy. (It’s not for a small garden, though!)

6. Go easy on the winter weeding. A layer of small weeds of a rather non-competitive type (like chickweed) conserves a warmer air layer close to the roots of your small plants.

7. Go Easy in Winter Fertilising and Watering, too.
Avoid it completely, if you can. Healthy plants survive frost better, but plants with soft new growth are more susceptible to frost. This is why a late spring frost can do so much damage, when the plants survived the same cold temperatures happily all through winter. The time for watering and fertilising - if you need it at all, is the part of the year when there is no risk of frost.

8. Consider soil moisture. 
Light, dry soils get cold more quickly. If the soil freezes, it kills some roots. This effect is greatest on shallow roots, and therefore on smaller plants. Moist soil protects from frost to some degree as it keeps a more even temperature. So how do you manage to have damp soil, without springing the plants into dangerous growth? Well this is obviously tricky, with our dry winter climate. Preventing moisture loss with mulch is an obviously sensible technique. shade and the shelter of low plants can help, too. Even a little moderate watering, when there is no sign of a warm spell is usually not enough to cause out of season growth. Planting the toughest plants in the driest sites is also something to consider. In all, there's no easy answer to the problem of having just the right soil moisture.

9 Plan for suitable mulch.
Mulch can make frost worse, or help plants survive, depending on what it is made of, how damp it is, and how thick.  Some mulching materials (stones, sand, dry organic mulch) cool down faster than others, sucking warmth out of the nearby air and the surface soil and losing it to the frosty air. They can cause unnecessary losses to frosts. Slightly damp mulch, like slightly damp soil, has a protective effect.. A thick blanket of organic mulch is better than a thin one. It may frost on its dry surface, but keep the plant roots safe below in the moister lower layers, and the soil below.

10. Consider the Sun.
Frost reaches its coldest point just before the sun begins warming the surrounding air. Depending on their species, plants can tolerate a certain amount of freezing of their tissues if they warm up gently.  This can be why one of two apparently equal plants may suffer while the other one escapes. The one with more early morning shade isn’t damaged like its sun-warmed neighbour. Placing semi-hardy plants where they are sheltered from the early morning sun can sometimes be just enough to save them. Knowing this, you may be able to extend your planting our into currently frosty sections of garden.

11. Cover your plants before frosty weather. Or not, as the case may be. Don't take it for granted that you need to do this at all.  Clever planting and garden management might mean you never need to. However, if you want to use this technique, real security comes with three good stakes supporting metre-high hessian walls, and a flap to make a roof at night. (Make the flap sloping, so the frosty air runs off. Remember that plants need sunlight, too, though not necessarily every day in this dormant time of year.)
If you are prepared to take a chance, an ordinary, inexpensive plastic tree guard, with three bamboo stakes may be all the shelter your plant needs, until it has grown out its tender baby stage. A rather floppy job, with one low stake allowing the top to lean inwards, helps keep the coldest air out.

12. Run to the Rescue.
Despite all your careful planning you are assailed by sudden doubt! The night was clearer, and colder than you thought it would be. A frost is sure to follow. Will your plants survive?  Plants be saved in the early light of a frosty morning, by being watered with cold water from the tap before the sunlight hits them. Water in the plant tissues may be frozen by the frost. Some plant species can tolerate a certain amount of this, so long as they are melted gently. Tap water brings them up above freezing point before the sun gets a chance to warm them up at a damaging speed.

13. Predict the danger of a Sudden Cold Snap.
Plants which have been subjected to a series of increasingly cold nights slow their growth rate down, and so have less soft new growth to get damaged by frost. A sudden cold change catches plants unaware, with their fresh growth all vulnerable.  Watching weather predictions can help us to predict when extra care is needed.You may want to put temporary covers on if a spring cold snap is predicted - or simply plan to be out early with the hose, giving the foliage of susceptible plants a good wetting.

14. Consider commercially Available Frost Protection Sprays. These are claimed to work, letting plants survive temperatures as much as  4°C lower than they could normally cope with. (I have have considered - and rejected - them so have no experience with them. You may choose otherwise.) They are costly, so I imagine they would be most used to nurse precious little plants through their first season or two, rather than in any general way. As with so many commercial garden products, though, you will never really know whether your money was well spent. Perhaps the plants would have survived after all, without it!

15. Surviving BLACK frosts.
Those horrible sneaky things! They don’t happen often, but when they do, they are invisible. We feel so cheated when our plants begin to die, just when we thought we had escaped the frost.
Visible frosts  are made of frozen water. That's why they are white. There is usually at least some moisture in any air. It settles on the plants as the air gets colder overnight, and then turns white as it freezes. But if the air is very dry it can reach freezing temperature with no white frost to reveal its presence. What is worse, dry air freezes more quickly than moist air, so a night of the same overall temperature has a colder bottom layer. The moisture in the plants' leaves freezes, just as it would with a white frost, but we can't run to the rescue with a hose because we don't realize that it's happened. That's a "black" frost.
All the above management techniques work, though, just as they do with white frosts.

16. Take a few Risks.When in doubt, plant it. You have nothing to lose but some plants, and you might be delighted by your unexpected successes. Our local native plant species are relatively untried in garden situations, but are proving to be hardier than it was once thought.

“Frost Hardiness” Labelling 
   Why is it often unreliable? 

Labels and lists which state that certain plants are frost hardy certainly help us choose better. However we need to keep in mind that we may lose some plants that "should have been" hardy, according to the written information.

On the other side of the coin, many plants which can really cope with our local frosts are sold with “frost tender” written on their labels. Understandably, plant sellers would rather err on the side of caution to save themselves from being accused of leading people astray. This means that we might avoid planting many lovely plants which really could have grown perfectly well in the relatively mild frosts of our own climate. 

Predicting how plants will survive all kinds of frosts, in all situations, is an impossible task.

Here are some of the Variables:

The meaning of “Frost Hardy”.
Some people call a plant frost tender if it might suffer “frostburn” on just a few leaf-tips. Others consider that any plant that is not actually killed is frost hardy, even if all the above-ground parts of the plant are destroyed. Many plants are designed to to exactly this, and can survive very hard frosts. Partial death is their frost survival technique.
(Typical examples are deciduous trees, and the traditional herbaceous perennials of our European gardening tradition.)

Degree of Frost.
Some places have colder frost than others. A plant that is "frost hardy" in a typical Toowoomba frost (perhaps -1½°) might not survive a -8° frost at Oakey. Lists of supposedly frost hardy plants from a coastal source will include plants that would never be put on a list made up by someone from the granite belt. Knowing where the frost advice comes from can help us decide how a plant would cope with our own conditions.

Some plants are frost hardier than others of the same species. Just as with people, plants vary within the species. Ones whose parents grew in frosty areas are likely to better survivors than the apparently identical plants, whose ancestors had it soft. Try to get plants of local native provenance, and be aware that the “same” plant, selling in a commercial nursery, may not be quite the same, really. Your local plant may do better than the one the nursery has chosen to label "frost tender".

Plant Height vs Freezing Air Height.
We only actually notice frost when it lies white on the ground, or on the plants, but really it’s the cold air that is the “frost”. At the end of a night, the lowest air is the coldest. Frosts occur when that lowest layer is below freezing point. The height above the soil surface of this below-freezing temperature air varies. A showy white frost can form at the bottom of a layer of freezing air that is only ankle deep. In this case, the only plants to suffer serious damage are the little ones. On the other hand, if that layer of freezing air is two metres deep, plants can be damaged to the height of those two metres. The depth of the frost can vary considerable even in a small garden. Think of it as behaving like floodwaters. There are places where the cold air will make deep pools, and others where it will flow away quickly and never reach a great depth. This means that you might lose one of two identical plants, just because that one is situated in a spot where the frosty air gets deeper. It is difficult to create labels and lists that reflect this reality.

Age of Plant. 
In nature, baby trees and shrubs in frosty areas tend to establish themselves in small, sheltered micro-environments. A clump of grass uphill can be enough to do the trick, dividing the flow of frosty air, and leaving a small warm pocket in its lee. By the time they outgrow the shelter, the young trees’ deeper roots and higher canopies keep them out of the way of that ground layer of freezing air. but of course the crucial height varies from species to species. Labels and lists have a problem being accurate about at just what age which species can survive what degree of frost.

Your own management techniques.
No label or list can hope to be exactly accurate about all plants, in all conditions. How can a stranger know how dry your soil, how well you manage watering, what kind of mulch you use etc, etc.

Think of plant labelling as a guide to managing plants, not as a guarantee that plants will perform in your garden exactly as the label and list-makers expected.

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