News

What To Grow In A Greenhouse

Jul 15, 2022

To get the juiciest fruit, the most flavoursome vegetables and the most potent herbs and spices, many people choose to get their own produce from greenhouse growing.

These handy little buildings give gardeners a controlled environment, allowing them to change the temperature and humidity to better suit their plants. This even means being able to create summer-y conditions in the depths of winter, allowing for longer growing seasons, or the ability to grow warm season crops that simply wouldn’t survive in typical New Zealand weather.

In short? Plants grow better in greenhouses because the conditions are better for longer compared to the outside.

This also means that there are heaps more plants to choose from when growing inside a greenhouse. Everything from chilli peppers to grapes to green onions and spinach can find a happy home in a greenhouse.

child watering plants in a greenhouse

Feeling spoiled for choice for your vegetable garden? Here’s a few places to start:

Remember the basics

A greenhouse is an excellent way to extend your growing seasons and get more control over the environment of your plants, but it’s important to know that the basics of gardening still apply.

Seeds

You can plant a wide variety of seeds in a greenhouse, but the quality of the seed makes a big difference to whether or not they’ll actually germinate. Even in perfect conditions, seeds that are out of date or poorly stored will have a hard time growing. Read more about preparing your garden shed to ensure that your seeds are well-protected.

  • Age of the seed. You’ll be able to store most seeds for about a year or two before they will start having trouble germinating once planted. You’ll either need to plant them quickly, or plant more of them to ensure a good crop.

  • Type of plant. The species of plant you’re trying to grow in your greenhouse will make a big difference to their use-by date and chances of germination. Seeds like corn and peppers are pretty much guaranteed not to do well after the two-year mark, but carrots and potatoes stay viable for up to four years. The real cream of the crop, however, are lettuce seeds and cucumber seeds, which can last for up to six years. Every species will have their own individual use-by dates.

  • Seed storage. If you want your seeds to grow, you have to treat them well before they even get into the ground. Keep your seeds in a cool, dark room, such as in a garden shed, for maximum viability. The vegetable drawer in your fridge is also a smart place for storage.

 Vegetable seedlings

Water

Overwatering or underwatering seedlings is a classic gardening mistake, and it applies to greenhouses too. Too much or too little water, and they’ll slow, stop or even reverse their growth. Some plants are thirstier than others, while others are easily overwatered. Keep an eye out for drooping or wilting, and water your seedlings appropriately.

In a greenhouse, it’s especially important to get your watering quantities and amounts correct. Unless you’re using an automated watering system, you can’t rely on the rain to water your plants for you. Make it a regular part of your routine to visit your growing plants with the hose and watering can ready.

Soil pH

This is the number one thing that most beginner gardeners overlook. A pH that’s too high or too low for a given plant will slow down germination, and worst of all, there aren’t any obvious signs that it’s happening.

Make sure to check the pH of your soil regularly, and double check if you’ve noticed your seeds are germinating too slowly. Even when you have more control over the soil in your greenhouse, the pH can change and require adjustment. Soil strips are a great investment, while limestone and simple compost will help you adjust the pH to where you need it to be.

Easy to grow greenhouse fruits

Strawberry plant
Strawberries

Now you can enjoy the classic pavlova topper all year round! Strawberries thrive in greenhouses, experiencing less pest and disease damage and tasting far better than those bought from a supermarket - especially compared to when you’re buying out of season.

Quick tips

  • Allow bumblebees into your greenhouse for improved pollination.

  • Plant your strawberries in pots with good drainage and plenty of organic material.

  • Use drip irrigation or a spray bottle to water strawberries as they have shallow roots.

Raspberries

Raspberries are fantastic additions to your greenhouse and happen to be one of the fastest fruiting greenhouse plants you can buy in New Zealand. In fact, they can fruit in their very first year of maturity! 

Quick tips

  • Keep conditions relatively cool for better growth for raspberries.

  • Use drip irrigation rather than overhead watering, as overhead watering can cause rot.

  • Harvest and use the raspberries quickly, as they don’t last long. Consider freezing them for extended storage.

Peppers

Bell peppers are an especially ripe addition to a greenhouse due to their need for long, warm days, much like tomatoes. They're one of the best heat loving plants. With a greenhouse, you have enough control to fulfil their sometimes-finicky temperature requirements.

Quick tips

  • Keep an eye out for aphids on the leaves, as their secretions can encourage the growth of black mould.

  • Make sure you water regularly and on a tight schedule. Don’t let the soil dry out.

  • Picking your peppers often will encourage growth, so don’t be shy about picking when they produce fruit.

Cherries

Cherry trees are a fruit species that can thrive even in pots, making them an excellent choice as greenhouse plants. They’ll likely develop into something closer to a cherry “bush”, making them a better fit for the smaller space of a greenhouse.

Quick tips

  • Keep your greenhouse ventilated and fertilise your cherry plants once a year.

  • Don’t allow your greenhouse temperature to rise too quickly, especially in summer.

  • Be patient! It can take up to 3 years before a cherry plant produces mature fruit.

Melon

Melons are a classic New Zealand summer fruit, but who says you have to wait for the hotter months to roll around? Planting melons in a greenhouse means you can enjoy them even in the winter. The key is getting the temperature and moisture level right - something which a greenhouse is perfect for.

Quick tips

  • Use loamy and well-drained soil for your melons.

  • Plant dill alongside your melons to ward off pests, but keep them relatively well spaced to reduce competition.

  • Keep an eye out for a crack in the stem where the fruit is attached - this means your melon is ripe and ready to eat.

Grapes

Ever fancied your own vineyard? With a greenhouse, a miniaturised version is possible! And even if you’re not keen on the idea of making wine, table grapes are a delicious addition to your fruit bowl too.

Quick tips

  • Plant your grapes on the opposite edge to the door, then train the vines up the roof and along the roof ridge towards the door for maximum growing space.

  • Remove any curly tendrils that begin to appear around flowering time. 

  • Water your grapes every 7 to 10 days throughout the growing period.

Chilies

Red hot peppers need a very long and very hot growing period for maximum spice and flavour. They're surprisingly tender plants, and their growing environments are ones that we just don’t get for long enough in New Zealand - unless, of course, you have a greenhouse, in which case you can grow them year round.

Quick tips

  • Germination takes up to 10 days, after which you should trim the main stalk once it hits 11 to 15 inches high to promote side shoots (and therefore more peppers).

  • Keep an eye out for whiteflies and use sticky tape to remove them if spotted.

  • Leave the peppers themselves on the plant until needed - they retain their potency much longer this way.

Oranges

If you’ve ever wanted fresh orange juice even in winter, then a greenhouse might be the answer to your prayers. 

Quick tips

  • Citruses like oranges are sensitive to dampness, so ensure that you don’t overwater your citruses, particularly during winter.

  • You likely won’t need to prune your orange tree for the first two or three years, so stick to shaping pruning only.

  • When harvesting, make sure to leave a nice clean cut on the branch with secateurs, as roughly broken stems are a vector for disease

Raised garden beds in greenhouse

Easy to grow greenhouse vegetables


Carrots

Carrots are incredibly versatile both in the kitchen and in the garden. They’re an especially good choice for an unheated greenhouse, as they are frost resistant, but they can be grown year round in a controlled environment.

Quick tips:

  • Use sandy, loose and deeply tilled soil. Don't let soil moisture build up.

  • Check carrot seeds especially well for disease, as it can be tricky to find chemicals that are effective on diseases for carrots.

  • If you find infected carrots, consider harvesting the rest of the uninfected crop early to minimise harm.

Cucumbers

Crispy cucumbers in your next salad or sandwich are just a sprinkle of seeds away! For cucumbers, it’s very important to ensure that their root systems are unobstructed, so make sure you have plenty of space before planting.

Quick tips:

  • Propagate cucumbers in peat pots, not in flats.

  • Keep an eye out for spider mites and their webs. Use insecticidal soaps to deal with them.

  • Try triple stem training or lateral growth training to better control the vines.

Green onions

Green onions are dead easy in terms of greenhouse growing, requiring little to no maintenance, being almost “set and forget” once they’ve started. This is the ideal beginner greenhouse plant.

Quick tips:

  • Consider growing your green onions from sets rather than from seeds - it’s much easier.

  • Always use well-draining soil and water your onions regularly.

  • Onions need about 10 hours of sunlight a day, so make sure to pick a sunny spot.

Asparagus

Asparagus are capable of producing for more than 20 years after they’ve reached maturity. Now that’s efficiency, and they perform even better in the confines of a greenhouse.

Quick tips:

  • Never plant crops in the same area as asparagus. They don’t perform well under competition. They can be grown outdoors as well, so feel free to move them outside.

  • Plant asparagus from a one- or two-year old crown for best results. Soil, pots or raised beds are equally suitable.

  • When harvesting, leave some of the smallest spears so the asparagus can grow again next year.

Spinach

Spinach is a great choice if you don’t want to deal with many pests. These are tough, hardy plants that thrive in cool conditions during their usual growing season, so they’re great for unheated greenhouses as well. These are some easy to grow salad greens that are a great option for a cool season crop.

Quick tips:

  • Use soil with good draining and position your plants/greenhouse in full sun for best growing.

  • Don’t let the soil temperature reach higher than about 21 degrees celsius.

  • When harvesting, only remove the larger, outer leaves, and retain the smaller leaves for continued growth.

Eggplants

Also called aubergines, eggplants are like peppers and tomatoes in that they are warm season vegetables - so keep your greenhouse heated up if you’re planning to grow them.

Quick tips:

  • Use raised beds to ensure the soil stays warm enough for your plants.

  • Use stakes or cages to keep your plants upright, especially after they start developing mature produce.

  • When harvesting, cut the eggplant’s stem about an inch away from the fruit. Don’t pull the eggplant.

Zucchini

If you want to see results, fast, zucchinis are the vegetables for you. They only take three to four weeks to develop, meaning you could be enjoying fresh greens from your greenhouse in only a month’s time.

Quick tips:

  • Space your zucchinis about two feet apart to give them enough room to grow.

  • Use stakes to keep them propped up.

  • If necessary, be ready to move your larger zucchini plants into bigger containers. They really love their space.

Tomatoes

Knowledge is knowing that tomatoes are technically a fruit, but wisdom is knowing not to put them in a fruit salad! However you enjoy your tomatoes, they make for a popular addition to a greenhouse crop, as growing tomatoes requires some fairly high temperatures and a long growing season to get the best results.

Quick tips:

  • Use well-draining soil and keep it moist (though not waterlogged) for a happier tomato.

  • Keep the temperature of your greenhouse around 21 to 24 degrees Celsius.

  • If using pots, plant a single seed in each pot to encourage thicker, stronger vines when growing tomatoes.

FAQ

Can you grow in a greenhouse all year round?

Yes! A greenhouse provides you with total control over the temperature and humidity for your plants, making it possible to grow all kinds of different fruits and vegetables all year round.

Can I put my greenhouse on soil?

Yes, you can put one of our greenhouses on soil, allowing you to use it for growing crops without having to add raised beds or pots. You may still want to invest in seed trays for some plants, however, and ensure that the soil doesn't get temperature fluctuations if you're using the greenhouse year round.

How do I keep my greenhouse warm at night?

Simply shutting the door at night will keep your greenhouse warmer, or you can use raised beds in your greenhouse to better protect the plants themselves. Alternatively, you can use a heater, but we recommend ensuring you have one with good temperature control. You don’t want to overheat your plants by mistake.

Alternatively, there are lots of plants that still grow well in an unheated greenhouse.

When should I start planting in my greenhouse?

You can plant in a greenhouse anytime! You’ll want to check the growing conditions required by your chosen plants, and some of them will require more sun than is possible to get during certain seasons (e.g. lemon trees thrive with 12 hours of bright sun, which can be tough in winter).

If your first choice doesn’t work out, don’t worry - there are heaps of other options for planting in a greenhouse. Try something different!

If you have any further question, get in touch with one of team here at Outpost Buildings today.

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