AUGUST IN THE TUNNELHOUSE, SPRING COUNTDOWN BEGINS!

May 19, 2023

August in the Greenhouse!

Welcome to Morrifield’s monthly garden guide where we go undercover to bring you the best tips and tasks for great greenhouse growing. While wild weather continues in many parts of the country, spring is just around the corner, and early bird greenhouse growers are already preparing for it!

Morrifield’s Gardening Zones

Our long maritime country is filled with exciting microclimates. That means your gardening zone may be quite different to your neighbour’s’ just a few kilometres away. Use our simple descriptions to help gauge which undercover zone sounds like you!

Zone 1 (Warm Winters, Hot Summers)
Zone 2 (Mild Winters, Hot Summers)
Zone 3 (Cold Winters, Mild Summers)
Zone 4 (Severe Winters, Hot Summers)

Top Tasks Around the Country

All Zones

Prepare supports 

Don’t leave it until your greenhouse plants are in place before installing supports – they won’t thank you for the disturbance, or for having their roots compressed as you tread on the ground. If you’re growing climbers, such as cucumber and vine tomatoes, your greenhouse purlins may be strong enough to take the weight of fruit-bearing plants, in which case you can tie support twine to them. (The purlins of a Morrifield tunnelhouse are suitable for this purpose.) Always choose light, rather than dark twine, so that heat is not concentrated where the twine meets the tunnelhouse skin (something which can reduce the life of the covering). 

Where necessary, create your own ‘purlins’ by running lengths of number 8 wire below the ‘ceiling’ of your greenhouse, and attaching them to the frame if you consider it strong enough. If your greenhouse is covered in plastic (or a similar heat-sensitive material) be sure to keep the wire ‘purlins’ well away from this in case they heat up and melt surfaces. Tip: to cut number 8 wire, use a sharp file to create a groove. Then, work the wire, either side of the groove, back and forwards until it snaps.

Stakes can be used to support taller plants in the greenhouse. Plastic-coated metal stakes are strong, easy to push into the ground, and should have no sharp edges that could damage the skin of your structure. Bamboo stakes, especially if grown locally or on your own property, are a sustainable option. If you plan to grow determinate (bush tomatoes), cages will prevent sprawl, and hold plants off the damp ground, reducing the chance of fungal disease developing.

Recycle clean-up

There’s every reason in the world to recycle greenhouse infrastructure such as stakes, cages, and inorganic strings and ties (don’t rely on organic strings from a previous year – they will not be strong enough to support plants for another season). However, if reusing materials, don some protective, waterproof gloves, and give your equipment and ties a good wash down with household bleach (diluted according to instructions).

This will help kill off fungal spores. While you’re at it, wipe your sanitising mix over any irrigation equipment you have in the greenhouse.

Install irrigation

Unless you are growing on a large scale, or don’t have the ability to wield a watering can, hand watering at ground level is always best. It puts you firmly in touch with the state of your soil, avoids over watering, and provides an opportunity to check on plants, pests and disease, as you work. However, irrigation does have its uses, especially if you plan to take extended breaks away from home during the growing season. When choosing greenhouse irrigation, always opt for a system which delivers moisture at ground level. Overhead sprinklers are a recipe for disaster in the greenhouse, wetting foliage which should remain dry, and inviting in disease that comes with high humidity and damp conditions. 

For those who are not on mains pressure, or who don’t have enough water pressure in their domestic system to operate an irrigation system, check out the submersible Aqua One pump available from Mega Mire 10. It can lift water from a barrel close to the greenhouse, and deliver it to plants). 

While it’s best to personally check on soil moisture levels before watering a greenhouse, this isn’t always an option. In which case, an automatic timer system is also a worthwhile investment.

Zones 1 & 2

Start seed raising!

Don’t leave it too late to raise your greenhouse seedlings – if you do, you’ll be heading to the garden centre, and paying premium prices for plants you could have grown yourself. One of the best purchases a thrifty greenhouse grower can make, is a propagating board or pad. These start at around $35, and they not only hurry along germination, but give seedlings the best start in life. Team your propagator with a garden thermometer to help you gauge the perfect temperature for germination. Cucumber seed germinates best when soil temperature is between 20 and 30°C. Tomato seeds prefer 21-23°C, and capsicum, chilli and aubergine germinate when soil is around 27-32°C. To adjust the soil temperature of seeds on a propagator, use a cake cooler to raise containers off the heat source. Alternatively, place a clear container over pots of seed to trap in extra warmth. Be aware that soil temperature changes throughout the day according to how strongly the sun is shining, so use your thermometer, often, to check.

Zones 3 & 4

Chop, drop & dig!

Cover crops are the natural way to fertilise your greenhouse soil, and August is the month to dig them back into the ground. If you grew mustard greens or broad beans, you’ve doubled the potential for good. Mustard greens exude sulphur-containing compounds which help cleanse the greenhouse soil of pathogens. Broad beans plants harvest nitrogen from the air, and deliver it back to the soil as plant material breaks down. 

Use shears to cut down and snip up your cover crops. Use a sharp spade to slice up roots. Mix everything into the soil, and water the ground thoroughly to speed up decay (water every couple of days for a week if the weather is warm and the soil is drying out). Your cover crop will break down in 2-4 weeks depending on weather conditions.

Welcome in the cold!

August is the coldest month in many parts of the country, and while we want all the heat we can get in the greenhouse at this time of year, chilly temperatures are also an opportunity to naturally kill off over-wintering pest bugs. Your winter veggies won’t mind if you open the greenhouse doors and windows on warmer days (just be sure to close everything up again before the sun goes down). And a fresh breeze will send the white fly packing in no time at all!

Hello, hydroponics!

In colder parts of the country, the wait for greenhouse soil to warm up, can be frustrating. One way to get a head start is to set aside part (or all) of your greenhouse for hydroponic growing. When combined with a water heating system, hydroponics means your the roots of your plants can be growing in temperatures of 16-18°C on a chilly day! With a thermostatically controlled system, the warmth continues through the night, encouraging rapid growth. 

By sowing the seed of cool climate tomato varieties in winter, and growing the resulting seedlings, hydroponically, in the greenhouse, you can aspire to fresh tomatoes in December! If you plan to dedicate your greenhouse to hydroponics, consider designing its floor so it has a 1:40 rise. This will help water drain from growing troughs.

Going green

It’s a myth that garlic must be planted in the depths of winter. In fact, current thought is that it should be sown at the best time of year to avoid the now widespread allium rust. In cold regions, garlic is often best sown in September or even October. While you wait, break up cloves, and place them in a container in the greenhouse where the light will encourage sprouting. Alternatively sow the cloves into individual containers of potting mix, and place these in the greenhouse to give this valuable crop an early start. 

Sow me undercover now

Zones 1 and 2

Directly into the ground: cool season microgreens,  radish, spring onion, ‘Tasty Tendrils’ peas, peas (all other varieties),

In seed trays or bags for transplanting or moving outdoors later: ‘Alboran’ tomato, broccoli, cabbage, cauli, rocket, silver beet, spinach, peas (all varieties), potato, yakon. 

Zone 3 and 4

Directly into the ground: Leafy Asian greens (such as Chinese broccoli ‘Gai Lan’, mibuna, mizuna, pak choi, and tat soi), cool season microgreens, rocket, spring onions, strawberries, ‘Tasty Tendrils’ peas.

In seed trays or bags for transplanting or moving outdoors later: potato, yakon.

Transplant me undercover now

Zones 1, 2 & 3: 

kale, leafy Asian greens, rocket, silver beet, broad beans. 

Zones 4: 

Alboran’ tomatoes, lettuce, spring onion, spinach, microgreens.