GARDEN SOIL

GARDEN SOIL

We all assume soil is just soil, but it is a very dynamic and variable material that it is beneficial to understand exactly what we have in our garden so we can know how to use it to get the best out of it for our plants.

Soil is a mixture of sand, clay, silt, humus and stones and can vary in depth, colour, drainage properties and nutrients available. No two soils are similar as they will vary from one place to another depending on their location and history. Some soils in the south of the UK sitting on the chalk downlands have a high pH with problems of nutrients being locked up and unavailable to plants. Coastal soils are often very dry if there is a lot of sand in the soil and these are also very poor in nutrient availability as there is not much clay particles which hold onto mineral nutrients. Some parts of Scotland in the north and west have a high rainfall and poor drainage which favours the build up of organic peat layers causing poor aeration and waterlogging.

However, much of the UK has a fair mixture of sand, silt and clay which with the right management can yield excellent results. The ideal soil for optimum plant growth will have about 45% mineral sand, silt and clay with 5% humus and 50% pore space to allow good water percolation and gaseous exchange. This will allow a good environment for worms and other soil organisms, fungi and bacteria to thrive and create a good soil colloidal crumb structure so that added organic matter can be broken down into humus to improve structure and release nutrients.

Formation of soils

Soil formation is an ongoing process beginning with the weathering of rock. Volcanic rock subjected to erosion by wind, water, acid rain and ice creates small particles that get washed or blown down mountains till they accumulate in small deposits. Algae and lichens can then grow on these and when they die they add a small amount of humus. As the process continues the deposits grow bigger and support more organisms then higher forms of plants life such as mosses and ferns can grow. Eventually pioneer tree species will colonise the area with roots that can penetrate deeper into the parent bedrock below the shallow soil and help to disintegrate the rocks further.

Other soils can be formed as tides and rivers deposit sand and silt every time there is a flood creating alluvium plains which are usually very fertile. Retreating glaciers from previous ice ages left behind deep deposits of boulder clays found to be very fertile once cultivated, drained and the bigger rocks removed. Soils can also be formed from areas of deep peat and silt once drainage has been carried out, though peat soils lacking in clay content can be very low in available nutrients.

Clay soils may be subject to poor drainage and heavy to cultivate, but once well drained and organic matter added they can be very fertile as clay can hold onto and release its nutrients for the plants benefit. Clay particles are extremely chemically active playing a very important role in holding and releasing plant nutrients. However this activity is influenced by soil aeration, drainage and pH levels.

The optimum pH for healthy plant growth is about 6.5. Problems emerge when soil is too acidic (well below pH6.0) or alkaline (above pH7.0) as some essential nutrients are then locked up and unavailable to plants, and others may become too readily available in toxic amounts.

Sandy coastal soils may be very well drained, but can suffer in dry weather and lack of clay content means they are usually very poor in nutrients. Adding manure, compost or rotted seaweed can be very beneficial.

Soil improvements

To support optimum plant growth soils need to be well drained, have adequate organic matter such as manure or well rotted garden compost added to improve the soil structure and provide the means for healthy soil organisms from worms to bacteria to thrive.

Add a green manure crop such as mustard, tares, clover, ryegrass or phacelia in autumn or spring whenever the ground is free from crops. This will break up heavy soils and increase air space, improving the soil colloidal structure, as well as adding organic matter. Many of these green manures such as clover have nitrogen fixing bacteria on their roots which greatly increase the availability of nitrogen to the following crops. Crop rotation, liming once every four years for the benefit of brassicas, and adding fertilisers will all help to increase the soil fertility.

I am also a great believer in double digging two feet deep and adding well rotted manure or compost before planting long term permanent plants such as trees, roses and fruit bushes.

However those practitioners of the no dig camp at City Road allotments have certainly been getting very impressive results on their vegetable crops, so we must keep an open mind on the best practise way forward.

Plant of the week

Pinus mugo the mountain pine is a dwarf pine that will give character to rock gardens and heather borders. It is evergreen, easy to grow and associates well with rocks and other hard landscaping. It is very tough and tolerates a wide range of soils and exposure to winds. There are a range of forms, so make sure you get a really dwarf type for rock gardens.

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IN BETWEEN SEASONS

IN BETWEEN SEASONS

Wet soil surface continues to hamper working the soil, but when the sun shines and the winds blow the surface dries up just enough to get the spade out before the next shower appears.

The garden carries on enjoying the sunshine as temperatures begin to climb.

The allotment continues to provide plenty fresh winter vegetables with cabbage, sprouts, Swedes, leeks, kale, Swiss chard and salad leaves of rocket and other mixed leafy salads are still plentiful.

Fruit and vegetables from the freezer now supplements the fresh produce and makes room for other vegetables. Room is found in the freezer for kale leaves and beetroot picked a couple of weeks ago. Beetroot also makes a brilliant chutney, as does Victoria plums from the freezer. The kale which is high in iron and great to maintain good eyesight will be used in soups and stir fries.

Although we still have a few pumpkins from last year, one is now on the table destined for a pumpkin risotto with some left over chicken pieces and the chicken stock.

Anna got our last eating apple from store, a lovely red Fiesta marking the end of our home grown dessert apple crop, but we still have three huge boxes of Bramley cooking apples. This fantastic cooker stores a very long time even though we use the fruit on every occasion for crumbles, stewed apple, compote and chutney. I managed to get ten demijohns of wine brewed from the small, damaged, misshapen and bruised fruit deemed best not to put into store.

In the Garden

Rhododendron praecox has been magnificent as there has been no frost to blacken the early flowers. The bright mauve flowers are a great contrast to the yellow, purple and white crocus planted at its feet. Even the snowdrops continue to flower into early March.

My winter border with Cornus Westonbirt, Mid Winter Fire and the willow Salix britzensis has never looked better especially now the drifts of crocus are fully out as colourful ground cover.

The wet year of 2012 gave the border enough moisture to last right through last year’s hot dry summer so growth was very strong with the willows reaching eight foot tall. Although these bushes get cut right back to ground level, they still grow back again strongly every year.

Looking ahead

As the sun begins to show us some spring warmth it is a good time to plan ahead for this years fruit crops. A low polythene tunnel was erected over a two foot wide row of early strawberry Mae. This protection should enhance cropping, bring it forward by at least two weeks and as the polythene keeps the fruit dry botrytis should not be much of a problem rotting the fruit.

Recent wet weather has created a problem trying to find a couple of dry days to spray Bordeaux mixture on my peach tree to prevent peach leaf curl. The first spray went on during a warm sunny morning, only to see the rain coming in by afternoon, so I just have to keep an eye on the weather forecast to catch the next decent dry day. I will soon run out of time as the buds are swelling up and flowering will start very soon.

February gales were no problem as my damaged greenhouse has been cleared off site. The breeze block base will get some repairs before the new stronger greenhouse with 4mm strengthened tough glass arrives, hopefully my mid March.

In the meantime it is time to sow my tomatoes, which will have to settle for a warm windowsill for a few weeks. This year I will still grow my favourites, Alicante and Gardeners Delight and try the new golden cherry variety Ildi.

Broad bean Giant Exhibition Longpod can also be sown now. These find a warm spot at home, then go onto a windowsill as soon as germination occurs. Broad beans are quite hardy so they will go outside once the plants are a decent size. Similarly, sweet peas can also be sown indoors to get them started, but shifted outdoors as long as our mild weather continues.

It is the tomatoes that are at risk if the weather turns colder, so if they need more windowsill space my established geraniums will go outdoors as they are fairly tough.

Plant of the week

Ivy ground cover is perfect for creating an attractive maintenance free border. The low growing foliage is quite dense and soon smothers any weeds trying to compete. There are golden variegated forms such as Hedera helix Buttercup and Goldheart, silver variegation such as Glacier, and some varieties such as Hedera canariensis have large exotic leaves. The smaller leaved varieties make excellent ground cover in shrub borders, but take care as they will climb up the bushes in time. They will also climb walls and fences, but an annual trim back in winter will keep them in their place. They provide frost protection at ground level for my outdoor hardy fuchsias just in case we get a severe frost.

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FINISH OFF WINTER TASKS

FINISH OFF WINTER TASKS

The mild but wet winter will hopefully be ending soon and once the soil starts to dry out we can catch up on all those jobs kept on the back burner. My priority is to finish off the winter digging put on hold as the soil was always too wet and we never got any light frosts to firm up the surface.

There was plenty of good well rotted garden compost for those areas needing fertile soil, especially onions, leeks, potatoes, cabbage, cauliflower and beans. Sweet corn, courgettes and pumpkin also need a lot of compost but as they all get planted in late spring there is still time to compost and dig over their patch then sow a green manure of clover or tares. This has plenty of time to grow before it gets trampled down and dug in a fortnight before planting. I have always had fantastic results after a green manure crop, as the roots really break up the soil and allow aeration as well as adding humus and nutrients.

Many areas are just not ready to dig as my late sowings of autumn salad leaves have continued to grow and provide fresh leaves all winter, so they will remain in place till they run to seed.

Beetroot left in the ground has kept brilliantly so I was able to harvest as required, but now it is beginning to grow so it will be lifted for the kitchen, and once partially cooked can be frozen for future use.

Cabbage and cauliflowers for spring use are looking great, and some will be ready very soon, though I still have some autumn cabbage which overwintered just fine. Just as well as my winter cabbage January King was a complete disaster. They were not happy with the mild winter and most have now run to seed. The few that hearted up were a magnet for slugs as January King does not have a solid heart at ground level and slugs can easily set up home in the spaces between leaves and stem. I will not grow that variety again.

Rose bushes and climbers take advantage of any mild winter to start growing at the first opportunity, so pruning had to be done in January to be completed by the end of February. Anna managed to get a small bunch of rose flowers for the house that had survived the winter.

Apple tree pruning has also been completed and now it is the turn of my Victoria plum to have its crown reduced in height so I have less need to climb the tree at harvest time. Anna gets a wee bit anxious when I reach the top of the ladder then have to climb a bit more as there is always some fantastic fruit at the end of a long branch that just have to get picked.

Hopefully I am far enough into the season so that silver leaf disease is less likely to infect the pruning cuts.

My peach tree will also get some pruning to create fruit spurs closer to the framework as well as some formative pruning to maintain its fan shape against the south facing fence. I will then give it two fungicide sprays a fortnight apart to keep peach leaf curl at bay.

This years vegetable and flower seed order has been delivered, so I can now set up my propagation programme to remind me of the best times to sow each type. In a normal year I would be sowing tomatoes, onions and lobelia towards the end of February. However since my greenhouse got blown down in the December gales this is not going to be a normal year for me. My hope is that my new greenhouse will be delivered and erected before the end of March. Windowsills can take a fair bit of young plants, while we await this new greenhouse. If the mild weather continues my fifty odd geraniums can go outside as they are quite tough, but my fifty odd tuberous begonias are not so hardy, and there is a limit as to how many plants you can get on a windowsill.

Tomatoes and lobelia this year will have to be sown a few weeks later.

I have also ordered my Hytech onions as sets this year, as they would need warm conditions early on if grown from seed.

Plant of the week

Rhododendron dauricum has to be the earliest rhododendron to flower. This year it started flowering in January and continued right through February. It is one of the parents of the very popular rhododendron praecox which is in flower now. In a mild year these early flowering shrubs are a great bonus, but if a frost catches them it will kill all the delicate flowers. Both these rhododendrons are small evergreen (R. dauricum is partially evergreen) bushes growing to about four feet tall that appreciate an acid moist, but free draining soil. They are very hardy, but a sheltered spot will help to protect the early flowers if a frost threatens.

Painting of the month

Arthurs Plot is my fourth acrylic painting showing a City Road allotment plot. Two paintings are winter scenes and two summer views with this one getting the modern contemporary treatment, where I concentrate on a loose colour balance of attractive shapes and no attempt to show detail.

I hope to show this painting with many others at the Angus Open Studio event in late May.

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COLOURFUL CROCUS

COLOURFUL CROCUS

The very mild winter has brought spring forward by several weeks so we can now enjoy those early flowers normally blooming in late March. My established drifts of crocus started to flower in mid February. They are very hardy and a covering of snow will not harm them, but a severe frost or cold gale will do them no favours. North east Scotland seems to have missed most of the very wet weather affecting the south and west of UK, so our crocus just need a wee bit more sun to open up the flowers and let us know that spring is just about here.

Crocus species grow in many different countries all over the world and now cultivated varieties have been bred to provide us with very colourful displays in spring for our gardens.

Local authorities have also recognised the benefits of enhancing the beauty of the environment by mass planting crocus in drifts where ever space allows in verges, roundabouts and parks.

When I worked in the Darlington Parks Department, many years ago, the council had established a “Crocus Walk” in a deciduous belt of trees along the main road into the town. Residents were very proud of this attractive feature and in autumn several offered funds to extend the crocus displays further into the town. The council matched this funding and over the next few years our Ring road grassed reservations received masses of crocus bulbs to brighten up the town in spring.

After flowering it is necessary to leave the foliage alone so it can build up the corm to a good flowering size for the following year. Usually a period of six to seven weeks is ample before the leaves can be removed. However in gardens where crocus is in border soil leave the foliage till they begin to go yellow.

The show begins with the crocus species flowering about two weeks ahead of the large flowering hybrids. Cream Beauty and Blue Pearl really go well together, and enhanced with the pristine white Snow Bunting. Add some stronger colours to add character such as Ruby Giant and Whitewell Purple.

However it is the larger flowered Dutch hybrids that really add impact to spring displays. Although there are many varieties the most popular come down to a handful that are hard to beat.

Yellow Mammoth must be the biggest and brightest yellow, Joan of Arc the cleanest white, Flower Record a strong purple and Pickwick has always been my favourite striped crocus.

Autumn crocus

Some species flower in autumn such as Crocus pulchelus, Crocus zonatus and there is several varieties of Crocus speciosus in blue and violet colours. These all flower in late summer to  autumn before the leaves appear. They are all very hardy and leaves emerging in autumn will be fine over winter. Do not cut or remove the leaves until they die down in late spring.

They can be planted in drifts in borders or the lawn in good well drained soil and prefer full sun, though some dappled shade will still be fine. Planting can be done by splitting up overcrowding clumps immediately after flowering, or plant fresh new bulbs in summer.

The saffron, crocus sativus also flowers in autumn and has been in cultivation for centuries. However it was not grown for its flower displays but for the world’s most expensive spice, saffron.

Each flower produces three long red coloured stigmas which are removed and dried to make saffron. It is a very slow process as you need a lot of flowers, which usually only last about two weeks to gain any useful quantity of product. Most of the world’s saffron is produced in Iran which has the best climate and soils for its production.

Plant of the week

Cordyline australis is a half hardy palm tree from New Zealand. It is often started off as a young plant used to give height to a summer bedding flower display. It will establish and grow fairly easily, but it is best to lift up and replant in a large pot to overwinter in a frost free greenhouse. In its second or third year it can be left outdoors where it can grow and survive if in a sheltered spot. If the next few winters are mild it will survive and eventually grow to ten to twenty feet before it flowers. These are not desperately attractive so probably best removed as they can weaken the tree.

However every so often we get a hard winter which will kill the top right back to ground level, but do not dig it out as the roots usually survive to throw up new shoots within the next couple of years. My twelve years old cordyline reached ten foot tall but then died back in a severe winter. It survived to produce a cluster of five shoots which are now six foot tall. As this winter has been very mild it should live another year or more with the promise of global warming.

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