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A look at soil for Perpetual Carnations in the greenhouse

A look at soil for Perpetual Carnations in the greenhouse by Harold.

By now you should have chosen your type of pot that you are going to use for your plants, but if you are still undecided then I would urge you to read the article entitled Plant Pots by Brian Yates that is posted on this site. It will allow you to make an informed judgement be it Plastic of Clay.

Turning to the subject of what soil to use is a very stimulating and challenging issue and has been and will continue to be a great bone of contention. Some will say use a peat based medium, others a John Innis potting compost, and others will use sterile top soil, and to this some will have added their own secret and special formulas, such as spent mushroom compost, cow pats, ground up rubble and every other old maids concoctions known to the fairies under the sun to add to their soil. The problem arises when these weird and wonderful potions let you down because of an ever zealous extra handful either burns your plants or a handful less starves it to death, so we have to be a little more scientific in our approach to what we place in our pots.
But first we have to examine what are the needs of our plants in the way of nutrients that will sustain the plant through its life from a small cutting to the cutting of prize blooms. Nutrients that will keep the plant healthy and meet all its demands so it will grow and produce good flowers throughout its lifespan so let us pause and consider its needs.

For a start our plants will be grown in a pot of sorts in a greenhouse and that pot must contain all the essential trace elements required, it is not like growing a plant in the open ground whereby it can spread its root system to reach new sources of food, so the balance has got to be as near perfect as we can achieve.
Soil, dirt, earth, loam, call it what you like but this is the backbone of your mixture and makes up for around 80% to 90% of the pot contents so it has to be right. Is it going to be Peat, if so let us examine the Peat content and why it is so popular with most commercially produced composts that we see in our garden centres.
It is produced by rotted growing matter in wetlands and bogs such as moss, heather, and fallen woodland, so it is a complete organic matter that has excellent water holding properties and that is why it is so very popular as a growing medium, just look at the Fen District and you can see Britain’s breadbasket striving on peat. But the main problems with us taking this peat and using it in our gardens are, it takes 1 complete year for mother nature to replace just 1mm of peat and since a peat harvester will crop to a depth of 200mm it will take 200 years to replace, but first the ground has to become saturated before this process of replacing the peat can start as the land has to be drained before harvesting of peat can begin. Traditionally peat was dug for the purpose of fuel and we can see how devastating this was in the Norfolk Broads where medieval man mined the peat for fuel and now with its miles of flooded mines that we call “The Broads” that like to cruise in our pleasure boats are a prime example of indiscriminate plunder of the peat bogs.
But to make peat an acceptable medium for growing carnations it has to be mixed with other natural ingredients such as Sharp Sand and or Perlite to create a free draining medium that carnations require. So is it useful to search for an alternative to peat, as well as all the aforementioned we should remember the massive eco damage we are causing by stripping our peat bogs that could soak up enormous amounts of carbon monoxide that we release into the atmosphere each day through commerce and driving our cars.

Garden soil can be replaced a lot quicker due of course to the use of our compost heaps that we all have at the bottom of our gardens for disposing of grass cuttings, weeds, and other vegetable matter and is dug in each season to enrich the soil for growing our garden crops. In turn we add to the bulk of the soil. But what about the weeds you may ask, they grow at a horrendous rate out in the garden let alone a greenhouse where the warm environment is ideal for growing, so we have to search for ways to use our top soil without the trouble of weed infestation.
A Soil Steriliser seems to be the ideal answer. We can buy a steriliser taking up to 34 litres of sieved soil for around £300 that will heat up our top soil to 86.6 centigrade, and that will destroy all weed seeds and any soil borne pests. I know the price seems formidable but in the long run it should prove a cheap alternative to using peat or top soil that is not autoclaved. I was wondering if any reader may have one that they can give advice on its benefits prior to me spending out my hard earned cash for my machine, if so I would be glad to hear from you as I am sure would others.

There are other alternatives to use as a soil enrichment such as soil less compost, these are sold mainly by local authorities and are made from our green bag waste of weeds, and hedge trimmings, but once again it would have to be completely sterilised before use, and would need some peat or soil as a base. The process of making compost out of our green bag waste is, once collected it is fed into a large shredder which reduces the waste in size that aids the composting of the material. It is then heaped up in the open air and regularly turned to allow the micro-organisms to do its job, a heat of 60 degrees centigrade is created to kill weeds and plant diseases and after approximately 24 weeks the material has become compost, it is then screened to remove any material too large to use as compost and then bagged and called Pro-Grow soil. It must be remembered that this Pro-Grow is not a soil for use as the base for potting plants. It is a soil conditioner, just as our own dung heap but on rather a massive scale and is dug into the ground in the same way as we do with our own small compost heaps. So to use this medium is not an ideal solution. I would be very cautious in its use.

For plants to make healthy growth we now need to add a food source to it so we must now look to the Dianthus needs. Plants can only absorb food in a dissolved form, so normally the plant can only absorb its food in the form as simple salts, which are usually the salts known as inorganic. There are 3 plant foods which are definitely required for healthy growth and they are. Nitrogen, Phosphorus, and Potassium, known chemically as N, P, and K.

Nitrogen is the main constituent of the atmosphere, but cannot be absorbed by our Dianthus. There are very few plants with this knack and amongst them are the pea and bean, yet all plants need it, but only a trace element is required because an excess makes the leaves outstrip the growth of the root system and we end up with large sappy brilliant green leaves that are a haven for greenfly, red spider and all the other uninvited and unwelcome pests.

Phosphorus is an agent that promotes strong root growth and to add it to soil when the plant is young and in its later stages it assists the plant to come to flower early, it does not seem to worry plants if used in excess but that is not to say we have to place buckets of it around our plants to be watered in or included in our soil mixture.

Potassium (potash) has a counteracting effect of the effects of Nitrogen, especially by promoting disease and airborne pests. Deficiency in this element is easily spotted by the yellowing of leaves. It is advisable to apply moderate amounts to our mixture to balance good growth. A good source of potash is the ash from a wood fire held in the garden on bonfire night.

Lime is essential but not in the large quantities that one is led to believe so a light dressing to the mixture is plenty. It has the effect of releasing locked in food for the plant to take up.

We now got a mixture of soil/peat that is sterile and with all the elements included to give a balanced food for the plant but there is still another major addition that we need for good Dianthus production and that is drainage. We can use sand or perlite or both for this purpose as our plants require free drainage to grow into a good plant. Plants that are kept constantly in wet and humid conditions will not become or stay a healthy plant.

Sand and not any sand but washed quartzite Sharp Sand is the choice of the best growers. Builder’s sand has too much clay content to make it a free draining product to use, just continuously pat a mound of builders sand and see the water rise even if it looks to be dry, so do not use this sand.
Silver sand is also not advisable to use as it is made up of silica and is too free flowing and could soon leach out leaving our soil too water retentive.
Beach sand is a no no due to it having a high salt content; it would need days of washing to make it a viable alternative.

Perlite, this is not a trade name but a generic term for naturally accruing siliceous rock. The distinguishing feature which sets Perlite apart from other volcanic matter is that when it is heated to a suitable temperature it expands from 4 to 20 times its original size and takes on the pure white colour that we all associate with Perlite. Expanded Perlite has many other uses other than a horticulture aid and that being a loose filling insulation for cavity walls. In Horticulture use it is very light and provides aeration and optimum moisture retention for superior plant growth. It has a neutral pH and the fact that it is sterile and weed free makes it idea for container growing. It is extensively mined in the USA, China, Greece, Italy and Turkey.

So now armed with all these ingredients we can put together a mixture that will be well suited to growing carnations in a pot within the greenhouse. So let us make up some potting compost, by working with a (3 Litre 7 ½ inch 19cm pot for our soil and
a small 3 inch or 7.5cm pot for our Superphosphate and Bone Meal)
This mixture should allow us to fill about 10×3 Litre pots.
11×3 Litre pots of soil.
1×3 Litre pot of sharp sand
1×3 Litre pot of Perlite.
1×3 inch pot of ground Lime.
3×3 inch pots of Superphosphate.
3×3 inch pots of Bone Meal.
Mix thoroughly together to obtain a nice open mixture and now we have the ideal medium for carnation growing by pot culture.

There are of course an alternative to creating your own potting compost and that is the use of John Innes Composts.
John Innes is not a manufacturer of compost, it is just a range of composts that was developed at the John Innes Institute and named after a Mr John Innes who was a nineteenth century property and land dealer in the City of London. On his death in 1904 he left his fortune and estate for the research in horticulture excellence, by finding a solution to a good growing medium for plants and hence the composts are named in memory of this great benefactor to horticulture. The John Innes Horticulture Research Institute was initially based at Merton in Surrey but now is located at Norwich. It uses all of the ingredients that we use in our home made compost that are matched loosely to John Innes potting compost No2. If you use this medium then I would suggest you add a couple of scoops of Perlite to the compost to give it more aeration and a better open consistency. Of course John Innes compost is produced as John Innes Seed Compost for sowing seeds, John Innes Cutting Compost for placing cuttings in, John Innes Potting Compost No1 for potting on young seedlings, John Innes Potting Compost No2 for general potting of most house plants, John Innes No3 Potting Compost for shrubs, but we need to use John Innes No2 Potting Compost for our carnations.

Good crocking to the pot and for the pot to be placed on some sort of staging be it a couple of battens or some other elaborate mesh affair will assist in the best drainage.
In the summer, when the plants are at their most active, April to October it is advisable to water the plants with a weak solution of fertilizer such as tomato feed to keep a good balance of food for the carnation plant. A regular scarifying of the pots soil will keep away any moss that given the chance will grow and sap our plant of precious nutrients. The soil in the pot should be well watered a day prior to planting to allow it to drain nicely; to water when you plant will disturb or only compact the soil around the plant.

Although I have said this article refers to Perpetual Flowering Carnations being grown in a greenhouse it is also an ideal medium to use for Pinks and Border Carnations.

In conclusion, I have searched many tool hire outlets and have yet to find a hire shop that will hire out a soil steriliser, so it seems that if you want to try your luck at producing your very own sterile soil then you have to make a purchase for one. There has to be a niche in the market for such an item for hire, perhaps some multi national garden centre will take up the challenge. It is unfortunate that large garden centres do not have the insight on how to earn some revenue, but if you know of such a hire shop or garden centre hiring such an item please post on this website.

My thanks go to Brian Yates for giving me the inspiration to write this article, it seems at long last he has created an ongoing interest in the site, urging us all to contribute.

Harold
September 2008.