Archive | February 2013

Waterproof your garden

When the rain is pounding down, plants get a hammering and soil washes away

When the rain is pounding down, plants get a hammering and soil washes away

Where I live up here on Tamborine Mountain the wet season is well underway. We’ve already been through a wild cyclonic storm, three weeks back, which left us saturated, wind-wrecked and without power for several days. Now it’s starting again!

Like humans, plants can absorb only so much liquid and gardens can suffer badly during periods of prolonged, heavy rain. So here are a few tips to help you waterproof your garden.

Poor drainage is death to the garden so look to your soil. Mulch well with hay or straw at least twice a year to improve drainage. Do it more regularly if you are stuck with either heavy clay or very poor sandy soil (see my book How to Improve your Soil – The Natural Way on this website). If you live where there is a definite “wet season” mulch at least one month before the rain is likely to start. Keeping your mulch topped up also protects the soil from rain damage and erosion, while the open nature of a hay or straw-type mulch allows the sodden soil beneath to “breathe” and dry out between downpours.

If your soil is very heavy and poorly-drained; if the surface is impacted and muddy; if moss is growing there, you have a permanent problem that can only be solved by putting in drainage pipes and/or channels to get the water away from the bed. Poor drainage in one bed or area of the garden can impact on other areas too because when heavy rain falls instead of being absorbed into the soil it runs off, causing erosion and damage areas at a lower level.

Another solution to improving drainage in your garden is to make raised beds, using timber, brick or stone. Drainage pipes can be installed if required.

Plants have evolved to deal with heavy rain but it can knock new, young plants about badly if they have not had a chance to establish their roots. Herbaceous plants with succulent, fleshy, non-woody stems (such as impatiens) are particularly vulnerable. So if you know very heavy deluges are on the way, save planting anything new until the rain has lightened or passed. If you are only concerned about one or two or just a few plants it IS possible to give them some temporary protection – an upturned bucket, a piece of fine netting or muslin, shade cloth, even a light covering of straw mulch will do the job. Shade-loving plants will be protected by overhanging trees and shrubs.

Heavy rain washes away soil and nutrients. After a deluge, check your garden to see if soil needs pushing back or replacing. Fertilize to replace nutrients – the heavier the rainfall in your area, the more you need to top up the beds with organic fertilizers and soil enrichers such as blood and bone, fowl pellets or ruminant manure. Conversely, DON’T fertilize just before very heavy rain is due because instead of washing this deep into the soil it is likely to just wash it all away. Fertilizer of any kind needs a bit of time to be absorbed into the soil and taken up by plant roots.

Plants in deep, well-drained beds are better able to withstand long periods of heavy rain. Terraced beds are particularly well-drained. Rockeries are the best place for arid-zone plants, alpines and succulents but make sure you check after a deluge to replace any eroded soil or gravel.

If you have pockets of chronically poorly-drained soil in your garden and improving them is beyond you, consider filling the area with pots instead. I have such a corner in my garden and have turned it into a container-growing area, filled with life and colour that doesn’t depend on the soil beneath. Shrubs, flowers, vegetables and even trees don’t thrive in poorly-drained waterlogged anaerobic soil.

If you live in an area with very heavy, prolonged seasonal rainfall don’t grow unsuitable plants such as those originating in deserts or dry, rocky places. If you do want to grow these plants stick to containers or create terraces and well-drained rockeries.

If heavy rain is due, try to pick any ripe or almost ripe fruit and vegetables. Rainspots can damage the outer layer and leave the fruit or vegetable vulnerable to disease pathogens; strong rain and wind will also damage plants and knock fruit from the stems. Root vegetables that are ready to harvest should be pulled up just before, during or immediately after a prolonged downpour or else they may rot in the ground.

Tea leaves and coffee grounds are both excellent soil-conditioners that help make your garden beds better able to absorb water. Don’t throw them down the sink, put them into the compost heap or directly on to the garden.

Don’t use black plastic under mulch (whether soft vegetative mulch or gravel/stones) if you live in a climate with heavy, seasonal, monsoonal rain. The soil will become sodden and lacking in oxygen, and easily compacted when it dries out, and all this will adversely affect any plants growing through holes in the plastic. If the plastic is there to suppress weeds, do any planting in containers placed on top of the mulch or gravel, bearing in mind that should you ever change your mind and want to remove the plastic and turn the soil underneath into a bed, or a lawn, it will take a lot of hard digging!

After a prolonged heavy deluge check your flowering plants for damage. If roses, dahlias, chrysanthemums or any other flowers are hanging from bent or broken stalks, snip them off at once. Broken stalks offer opportunities to disease-bearing pathogens and certain harmful insects.

Don’t dig very wet ground. After a prolonged and heavy downpour, soil should be allowed to dry out to a manageable, crumbly, moist but not wet condition before digging, or its structure will be damaged (and it’s very hard work, too!). Don’t dig a garden bed before heavy rain is due, either. Good soil develops a light surface “crust” that protects it from damage or erosion during a downpour. Digging it over exposes the topsoil to all sorts of adverse effects.

Finally, learn the habits of plants. Some are better able to take up and utilize water than others. If you live in an area where heavy and prolonged rainfall is usual, where the soil is full of clay, where you have steep slopes and bare, exposed areas without vegetation, where the ground is naturally low-lying and swampy, then you need to take all this into account when choosing plants. Sure, do what you can to make improvements but there’s no point in fighting nature by trying to grow unsuitable plants.

Outside my window the rain is getting heavier – we are in for a long, wet night of it. But at least I can stay snug indoors, knowing that my garden is as well-protected from the deluge as I can make it.

In the wet season young herbs succumb easily to rain damage.  Grown in pots like this on a raised, dry surface they can be easily managed and moved under cover if necessary.

In the wet season young herbs succumb easily to rain damage. Grown in pots like this on a raised, dry surface they can be easily managed and moved under cover if necessary.

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Fire and rain

Red flower - these are born in spring and summer

Red flower – these are born in spring and summer

One of my three new young Metrosideros collina 'Fiji'

One of my three new young Metrosideros collina ‘Fiji’

If you want the ultimately tough but tasteful plant for your warm climate garden; one which looks good all the time and can take just about anything Mother Nature can throw at it, think about the metrosideros.

I recently had to make a tough decision. The tail end of a recent three-day storm – cyclone, hurricane, typhoon call it what you will – dumped about 30 inches (750 mm)on my garden. Yes people, that’s about London’s average rainfall for the whole year. Austin, Texas gets just over that amount for the whole year too while Los Angeles gets less than HALF that amount a year. And we got it in a couple of days! Combined with strong winds with gusts sometimes reaching 55 mph (90 km) or more, a lot of trees and shrubs lost limbs or were uprooted.

Among them was one of two large shrubs right in front of my front deck. These gave us privacy from the street and protection from the strong western sun but they were straggly things, too large for the bed and in constant need of clipping. They were also grevilleas and thus short-lived. So we pulled out both of them and then had to think what to put in their place in what was now a nice open bed.

After much thought I decided on the metrosideros ‘Fiji’, a cultivar of the little known Metrosideros collina var.’Vitiensis’.

I’ve long been a great admirer of the metrosideros, a genus limited generally to the Pacific, with most species occurring in New Zealand and one, I think, in South Africa. There is also a very beautiful, yellow-flowering tall tree species native to northern Australia (see my companion blog on rainforest plants) but this is outside the scope of this article due to its height (and has also been renamed as Thaleropia queenslandica). The metrosideros types I’m writing about here are those small-growing tough trees and shrubs with neat little leaves, dense growth habit and pretty red bottlebrush flowers. They bear some resemblance to the Australian callistemons (now classified among the melaleucas)and indeed are in the same myrtle family.

The best-known species is Metrosideros exclesa, a common hedge plant in New Zealand where it is commonly known as “pohutukawa”. This is a great screening plant because it can take strong winds, seafront conditions, heavy rain AND long, dry periods. Today there are several garden-friendly cultivars of this species available in garden centres, along with cultivars of other metrosideros species. They all take a lot of beating when it comes to attractive plants for marginal conditions.

I had a choice of several metrosideros types in our local garden center and finally opted for the ‘Fiji’ (indigenous to the Pacific area) because I liked its neat, dark green foliage with a slightly velvety texture when young. New growth is a rich burgundy. The red flowers are smaller than those of the M. excelsa varieties and make a less spectacular early summer show but I feel the small size (to 10 feet/3m maximum) and dense habit of this tree/shrub is more suited to the restricted space of a bed about 13 x 6.5 feet (roughly 4 x 2 meters). So I bought three, and set them off with a border of vincas in shades of pink and white (yes, I know the older vinca species can be invasive in some places but not the new, well-behaved, low-growing nursery types).

In this position, my new metrosideros will have to take the full force of the afternoon sun, westerly winds that can be very hot or very cold in season, heavy downpours of rain in summer and long, dry periods in winter and spring. They should be able to cope with all this very well, as well as temperatures down to zero Celsius for short periods – though not frost. Like all metrosideros types they need a well-drained soil and won’t thrive in heavy clay. They’ll do brilliantly in sandy, windy coastal areas, for which they have evolved, but they can also handle uplands back from the coast, and arid inland areas too. Their water requirement is low, they are great tub plants, and all they need is regular pruning to keep in shape. I plan to tip prune them when young to promote bushiness and, as they become mature, give them a hard cut-back in late summer-early autumn to promote the burgundy new growth for winter color.

And if we get any more wet and windy weather this season I’m confident my fiery-flowering little ‘Fijis’ will be able to handle it.