What To Grow In Your Greenhouse In September

When it comes to your greenhouse in September you can split your activity into two main areas - what to grow in your greenhouse and greenhouse jobs to get it ready for Autumn. Here is our advice to help you be efficient and effective and get everything in place for the cooler months ahead.  

What To Grow In Your Greenhouse In September - Sow Sweet Peas 

Sweet peas are a real favourite amongst gardeners and by sowing them in September / October you will get flowers earlier in the year, which are bigger, on stronger stems and plants which will flower for longer.

Sweet peas are fairly easy to germinate from seed when you grow them in your greenhouse, but they will be helped to grow into healthy plants with just a few simple approaches:

• first - remember sweet peas have long roots, so ideally they need to be sown where the roots will not be squished - so sow them in something like Rootrainers, or the Deep Root Success Kits rather than shallow seed trays.
• they don't need heat to germinate - even when you sow them in early autumn, the temperatures in your greenhouse should be sufficient - if sowing gets delayed until mid winter then a small amount of heat will be required. By growing slowly you should get a stronger plant which is what you are aiming for.
• be prepared to pot on seeds sown in the Autumn - you don't want growth to be damaged by your plants growing too big for their containers, so once they have completely filled the cells with a strong root structure, transfer them into deep pots, approx. 1 litre in size, so they can continue to grow unrestrained. 

28 Cell Deep Root Success Kit These 5 inch deep cells have been specially designed with their internal ridged sides, central drainage hole and four side ventilation slots to encourage a healthy root system to be established. Plants like sweet peas will really benefit from being grown in these individual cells ensuring their roots don't become entangled and they grow long and straight. Click here for purchasing details.

Sweet pea seeds have a tough outer skin, so you will often find gardeners who either nick the coating with a sharp knife or piece of sand paper, or soak them overnight to soften or those who just plant them from the packet. You will find conflicting advice online, but for us we see no harm in soaking them overnight - and as we have Nitrozyme ready for taking cuttings, we use some to enhance the soaking water for our sweet peas.  

What To Grow In Your Greenhouse In September - Sow Hardy Annuals Requiring Protection  

Depending on where you live in the UK will affect whether some hardy annuals can be planted direct into your garden or would be best to grow in your greenhouse - or in a cold frame or cloche.

Take a look at seed packets to help you make the decision - checking the temperature they will need to germinate - if you get these type of temperatures outside then all is good, but if you don't want to take a risk, start them off under cover.

The type of seeds which should be sown under glass include sweet peas (as discussed earlier), together with baby blue eyes, california poppies, toadflax, etc.

If the seeds you want to sow have high germination temperature requirements, rather than heating your full greenhouse you could divide it off by creating a 'curtain' of heatsheets. Or, if you don't intend to sow too many seeds, then the space provided by a heated propagator might be more than adequate.

What To Grow In Your Greenhouse In September - Take Cuttings For Free Plants 

September is a great time to take cuttings from a wide range of plants around your garden if you want to increase plant stocks or simply to ensure that you have replacements for those frost-tender plants which you like and which might not survive the winter months. 

“We often hear the question 'Which came first, the chicken or the egg?" For the gardener this would be 'Which came first: the tree or the seed or the cutting?'
Anonymous

The plants which you can take cuttings from in September include coleus, felicia, fuchsia, geraniums, hebe, lavender, penstemon, pinks, salvia, etc. These are just a few examples so simply select those plants you like the best ... and if you still have too many to choose from, then look at the health of the plants. Good cuttings should be taken from plants which are semi-ripe.  Woody growth will reduce your chance of success. Ideally you want cuttings from the current seasons growth which will be packed full of hormone levels for successful root formation. 

Taking cuttings from plants and succeeding in creating new plants this way is a huge topic, so we are only briefly touching on it here - we will cover this subject more fully in a separate blog post.

To help you succeed when taking cuttings, here are our top tips:

• Be Prepared - make sure you have everything ready before you take your cuttings.  A sharp knife or razor blade, potting compost, perlite, grit or vermiculite, and a propagator with good base heat if necessary  This will depend on the plant and the ambient temperature).
• Take a healthy cutting - usually this would be a non-flowering shoot from the main part of a healthy plant. 
• Prepare the cuttings correctly - the plant variety the cuttings are from will affect the length of the cutting you should take, which leaf to remove and where to make the final cut etc. 
• Place in the correct area - ideally your cuttings need to be placed somewhere they will get good natural light, avoiding direct sunlight.  Alternatively you can use a good quality grow light.
• Treat them well - so that's watering, but not to excess, pinching out the growing tip once roots have formed to produce stockier plants and leave in their pots / rootrainers.  If this happens before October then they are likely to need repotting during the autumn, otherwise they won't need repotting until spring. 

Perlite Perlite is a volcanic rock which expands to about 13 times its volume when heated up to 871ºC . During the heating process it 'pops' (similar to popcorn) to form a granular, white, light material. Each piece is composed of tiny bubbles, with the surface covered in hundreds of tiny cavities. This combination of bubbles and cavities enables perlite to absorb and hold moisture, nutrients and air and makes it so useful in gardening. Click here for purchasing details.

Some cuttings will progress better and faster if they are put in a propagator which provides them with a good base heat. So ideally you are looking for an electric propagator with base heat, thermostatic control and with a ventilated cover. It needs to be large enough and tall enough to accommodate your cuttings at least until they have rooted and are growing well. 

Greenhouse Jobs This Month - Stay Vigilant For Pests And Diseases

Even though your greenhouse is likely to be becoming less busy and congested with plants, it is still important to stay on top of any pests which may take up residence and make plans to prevent any damage or disease. 

“The key to good growing, especially to keep problems in check, is lots of shaking hands with plants. Don't just wave hello to them from ten feet away. Go touch them, look under a leaf or two, and notice the small changes that are the first signs of trouble.”
Courtesy of Janet Macunovich

If you are starting to bring in non-hardy plants which will need the protected environment of your greenhouse to survive the colder months, then check them first to make sure they are free from any pests - you should be checking for things like mealybugs, red spider mite, scale insects as well as the dreaded vine weevil. 

At this time of year, one of the diseases we have to be aware of and take action to prevent is botrytis. This is a white growth on plants which soon darkens to a brownish/grey colour and can affect many plants in your greenhouse when the environment is damp. Our recommendations to try to prevent this taking hold of plants in your greenhouse are:

• ensure adequate ventilation - allow fresh air into your greenhouse even though you want to keep cold out.
• water early in a morning - so plants, leaves etc. have time to dry before the evening, to prevent a damp, cold atmosphere which could encourage botrytis
• remove any decaying plant matter - dead leaves or blooms are best removed 

Try to stay on top of cleaning your greenhouse.  Clean dirty pots, seed trays and get rid of old water matting etc.  

Greenhouse Jobs This Month - Remove Shading 

We shade our greenhouse to protect the plants from being damaged if the sun is too strong or the temperatures are too high.  In the UK, from September onwards we need to start reducing the shading as the sun gets lower, the days get shorter and the temperatures become cooler.  

"September days have the warmth of summer in their briefer hours, but in their lengthening evenings a prophetic breath of autumn."
Courtesy of Rowland E Robinson

Store blinds or shading net away until they are needed again the following year - basically somewhere dry and mice free so they will be in good condition the following spring.

If we do get sunny days you can now start to control the temperature via ventilation whilst allowing your plants to get maximum light. 

Whilst you are removing the shading you also have the opportunity to give the glass or plastic a quick clean with some soapy water, removing any dirt (especially from where panes overlap) and if you see any damage to the glazing or missing glazing clips then now is the time to make a quick repair.

Greenhouse Jobs This Month - Check On Ventilation

Although we can never rely on the weather to provide us with consistent temperatures, now September has arrived we can expect more fluctuations. In order to keep your greenhouse a healthy environment for your plants - so neither too warm, too cold or too humid, check your ventilation is sufficient for the size of your greenhouse and that it's all working correctly.

Ideally you should have a combination of roof vents to let the hot air rise and leave and louvre windows to encourage fresh air to enter. At this time of year it's good to be closing the roof vents in the afternoon to capture the days heat for overnight and re-opening them the following morning.

Or you can simply control the opening and closing of the windows using automatic vent openers. 

If you haven't got a louvre window in your greenhouse, we highly recommend adding one. The easiest way to do this is to purchase a louvre kit.  

Louvre Window Kit Providing you with the metal components needed to enable you to create a louvre window in an existing greenhouse, simple DIY skills are sufficient to get this installed.   The aim is to use the glass you remove to form the blades for the louvre - so you could cut the glass yourself or if you are unsure contact your local glazier to see if they could do that for you.   Click here for purchasing details.

Greenhouse Jobs This Month - Make Sure Your Heater Works Effectively

Even when we have unseasonably warm days in September, we know that cold nights, evenings, and days will be coming soon, so now is the best time to check that your greenhouse heater is working, ready for when it's needed - and giving you time to get it mended, serviced or even replaced so you are not caught out.

You might have an electric greenhouse heater, or it might be a gas heater or a paraffin heater. Here we can take a quick look to check what could go wrong and the possible solutions. 

Electric Greenhouse Heaters 

Using an electric heater in your greenhouse is often the most efficient way to provide heat - the cost of electric might seem high compared to gas or paraffin, but with electric heaters you don't need as much ventilation, so not as much heat will be 'lost'.  Straight forward to use - simply plug in and and it's ready to turn on - so no gas or paraffin required or more importantly, to run out of on a cold day! 

When it comes to using an electric heater after it has been stored over the summer months, there are a few things to check to make sure it is going to work efficiently. 

Look to see if it has been damaged whilst it has been stored - with electrics you can't be too careful. So the first things to check are if there is any obvious damage to the cable, is the casing intact, is anything visible that could stop the fan from turning and find your operating manual and reacquaint yourself with how it should work. 

Check it operates - simply plug it in and turn it on. Does it start to produce heat? Does the fan turn if there is one. If nothing happens check the fuse first. You could then check the settings - whether it has a control knob to control heat or fan and the temperature it generates. If these all seem to be OK and you have had it a long time it probably needs replacing. 

If it includes a built in thermostat, does the heater maintain the temperature you set - most electric fan heaters for use in a greenhouse will have a built in thermostat and a control knob which you can use to set the temperature required. To check that the thermostat is working correctly you will need to use a max min thermometer in your greenhouse and test the heater for 24 hours and see if the thermometer records the temperature you wanted to achieve. 

If you want more precise control of the temperature than your current heater provides - this can be achieved by adding an external thermostat - just make sure it can control a high enough wattage to suit your heater.  

Thermo 2 Thermostat Able to control appliances up to 3KW, simply plug your heater into the front of the thermostat. The thermostat is then plugged in to the mains electric. Set your electric heater to maximum. Then set the temperature required easily with the up and down control buttons and the easy to read digital display.   Click here for purchasing details.

Propane Gas Greenhouse Heaters 

Propane gas heaters are a very popular way to heat a greenhouse and if this is your chosen method, then now is the time to take it out of its summer storage and give it a check over before you use it. As with all heaters we recommend finding and re-reading the manual which was supplied with the heater. After you have done that, here are a few common things to check to make sure it works correctly and safely over the colder months. 

Check the obvious things first - that the gas hose isn't damaged, bent or twisted or has any signs of deterioration, that the connection valves are fitted correctly and tight, that there is gas in your cylinder and that there are no leaks - use a specific spray product to do this NEVER USE A NAKED FLAME TO CHECK FOR A LEAK. 

Ensure there is adequate ventilation in your greenhouse - although this sounds contrary when you are wanting to heat your greenhouse, what you need to remember is, when a gas heater is operating it will generate lots of moisture and fumes. When these build up it will deplete the amount of oxygen in the air, which can stop the heater from working and can also damage your plants. 

Make sure your heater is clean before using it again - whilst your heater has been stored the smell of the gas remaining on the heater can attract insects and spiders to take up residence inside it and if they get in the nozzles or burner or just any small parts of the heater they can cause blockages which could prevent the gas from flowing correctly. So you could use a can of compressed air to blow away any debris or you could take it to be serviced before re-using it.    

If you have any doubts about how your gas heater is operating we would always recommend speaking to your local corgi registered gas engineer.  

Paraffin Greenhouse Heaters

If you use a paraffin heater in your greenhouse there are only a few things to check. 

• Make sure you have a supply of paraffin 
• There should be no rust - if you have an old rusty tank then you would need to replace the heater
• Check the wick - ideally we would say to fit a new wick if you have not used your heater in a while as a clean wick will burn efficiently and spare wicks can be purchased here - just choose the right one to match your heater 
• Make sure you have adequate ventilation in your greenhouse - paraffin heaters are used to produce a small amount of heat (so to keep a greenhouse frost free) but to work efficiently there needs to be adequate ventilation as they will generate high volumes of water vapour together with odours which you will want to escape. 

Our blog posts are created from our personal knowledge, information gathered by speaking to other gardeners or manufacturers in the gardening industry, by reading gardening magazines and devouring information from books and the internet. We aim to be as accurate as we can, so if you find a mistake, please remember, we’re only human. if you have any queries you can contact us today!