Growing Onions In Greenhouse – Planting From Seed, Bulbs, Sets

Growing Onions in Greenhouse

Hello gardeners, today we are here with a new topic so-called growing onions in Greenhouse. Are you interested in growing onions in your greenhouse? Well, this article may help you to know how to grow onions in the greenhouse. In this article, we also discuss all the requirements and related topics about growing onions in Greenhouse. Some of the information may be useful for growing onions in Polyhouse or any other controlled environment.

Introduction to Growing Onions in Greenhouse

Onions, the other name is Allium cepa and it is an underground vegetable and its bulbs have loads of health benefits. Onions are very easy to grow and can be successfully grown in a greenhouse. In this article, we will tell you how you can grow onions inside your greenhouse.

Onions are a very good source of flavonoids, phytochemicals, Vitamin C, and sulphur compounds. Flavonoids have lowered the risk of stroke and cardiovascular disease. The antioxidants in Flavonoids will also fight against cancer and acts as a natural blood thinner, and a lot more.

A Step By Step Guide to Growing Onions in Greenhouse

Guide to Growing Onions in Greenhouse
Guide for Growing Onions in Greenhouse (Image credit: pixabay)

Onion is one of the most popularly used home ingredients, achieving high-quality onions in your greenhouse is a very great idea for many households. Onion plants are very easy to grow, making them an ideal first venture for many gardeners. Due to their hardiness, onions are very perfect spring plant meaning that, come summer, you can even have access to delicious onions in the comfort of your own home or house.

Setting Your Onions Beds for Growing in Greenhouse

For a successful onion growth, you just need to prepare your onions bed in a greenhouse and you should just maintain your greenhouse temperature very ideal.  

Before planting the onions inside your greenhouse plant bed, fill your complete greenhouse onions bed with rotted garden compost, perlite, and horse manure. This combination may do many wonders. These need to be added to the surface layer because the rooting system of onions is very small and shallow.

Things to Remember While Growing Onions in Greenhouse

Greenhouse Soil Test

Onions do very well in a non-compacted, fertile, and well-drained sandy loam soil which a pH range of 5.8 to 6.8.

The Temperature of the Greenhouse

Onions are called winter plants and they prefer temperatures range of 12.7°C and 23.8°C. The greenhouse temperature should be adjusted around these ideal temperatures, especially, throughout the onion bulb formation; greenhouse planters can even use heaters or evaporation coolers inside the greenhouse to attain the maximum aforementioned temperature.

The onion germination will roughly take place in 6 to 12 days. In this process, you need to just set or adjust greenhouse temperature, during the day at 15.5°C – 18.3°C.

Set or adjust the night temperature of the greenhouse to 12.7°C to 15.5°C, when you see or observe the onions have started coming out of the bulb.

Water Requirement for Growing Onions in Greenhouse

Greenhouse Onions need a sufficient or required amount of watering twice a day. Though they are cool or cold temperature plants, irregular watering in stress conditions and hot weather or climate may result in bolting.

This does not mean to overwater your onion plant. Onions have a very shallow root system, which is developed with the course of their growing cycle or period. After the rooting is developed they do not need much water to survive.

Transplanting for Growing Onions in Greenhouse

Many of the gardeners like or prefer to grow onion seedlings separately in a seedling tray then transplant them into the greenhouse onions bed. But you’ll always sow your seeds directly within the beds.

We would recommend sowing your seeds in seedling trays then transplant them in your greenhouse onions bed.

Transplanting of seedlings should be done when onions reach a height of 6inches or 15cm and a diameter of about 1 inch or 2.5cm.

Transplanting of onions within the greenhouse be done a month after you’ve got planted the onion sets and forty to fifty days after sowing onions seeds.

Planting Onion Seeds inside the Greenhouse

Start sowing onion seeds from late January to February; follow the instructions of the onion seed supplier, within the greenhouse but not within the greenhouse onion bed. First, sow them in modular trays and place them over a heat bench within the greenhouse.

Take a modular tray or cell and then sow four seeds per cell. Propagation heat Mats also called root heating benches (Phytotronics Propagation Mat) give the simplest germination results provides a consistent temperature as compare to the heating plant inside the greenhouse.

After germination place modular trays outside when there’s no frost and place them back in the dark. Start hardening them in early May and space them during a staggered pattern 30 x 30 cm apart.

Growing Onions from Onion Sets in Greenhouse

In case if you miss this: Vertical Gardening In India.

Growing Onions from Onion Sets Greenhouse
Growing Onions from Onion Sets Greenhouse (pic source: pixabay)

Growing onions from the bulbs or onion sets are much easier than sowing or growing them from seeds. Before starting it first, you should know what onion sets are?

What Are Onion Sets Mean?

The onion sets are well-grown onion bulbs that are half mature and have already completed the initial growth period or cycle. You can buy onion sets from your local or nearby seeds store or you can even buy them online stores. For example, white onion sets, Wethersfield red onion Sets.

You should not buy onion bulbs or onion sets that have started taking out leaves and have started with the flowering process. This means the onion bulb you are going to buy should be good and very well. Many of the nurseries or even seed stores sell onion bulbs of different varieties and sizes, with a color range from red, white, and even yellow. Most of the time they will not specify the varieties of onion sets.

When to Sow Onion Sets for Growing Onions in Greenhouse?

You should start sowing the onion sets that you bought from a nursery or a store from mid-March to mid-April. You can even plant them directly onto the greenhouse onion bed or you can use a modular tray before hardening them off.

It is advised for you if you are sowing red onion sets it is much better to leave them till April as they are more prone to bolting and a later planting may help.

How to Pick the Best Onion Sets to Plant

The most crucial and important step is to pick the best onion sets from the ones you have collected so far. If you choose them very wisely at this step then there will be no chance of throwing half of them out of the greenhouse onion bed.

You should avoid using and buying onion sets with shoots.

You should not pick a scraggy onion set.

You should remove the ones which are having brown patches or molds on the surface of the onion set.

The selected onion set should not be very big.

Well shape rounded and tidy onion set is a good and perfect choice. You can go for it.

How to Plant the Onion Sets Inside the Greenhouse

  1. Greenhouse onions bed soil should be filled enriched with fertilizer, horse manure, and ideal soil as we have discussed earlier.
  2. First, prepare the onion bed soil, and then just spread a layer of compost 1 to 2 inches over the bed.
  3. Then with the help of a rototiller, you need to mix the compost into the top 6 to 8 inches of soil. Use a rake to smooth the soil surface.
  4. With the help of a trowel dig a 4 inches wide and deep trench in the soil bed.
  5. You need to cover the bottom of the trench with a 10-20-10 granular fertilizer at a rate of 1/2 cup per ten feet.
  6. Then again cover the fertilizer in the trench with 2 inches of soil.
  7. Pat the soil within the trench down firmly.
  8. Onions sets should be positioned in such how that the rounded ends face the bottom and therefore the pointed ends confront.
  9. In the bottom center of the trench, you need to place or push the onion set. That should be spaced 4 inches apart.
  10. By using a garden hose, water at a depth of 6 inches.
  11. At this stage, better to apply a 5-10-10 granular fertilizer at a rate of 3/4 pound per 25 linear feet of row.
  12. Again you need to dig a 1-inch deep trench down either side of the growing row of onions.
  13. Space the trenches 2 to three inches far away from the middle of the onion row.
  14. Measure out the right amount of fertilizer and divide it into two equal portions.
  15. Pour one portion of fertilizer evenly along the rock bottom of the left trench and therefore the second portion along the rock bottom of the proper trench.
  16. Backfill each trench with soil.
  17. Water the world thoroughly to activate the fertilizer.
  18. Cover the onion beds with a Planting mat and therefore the mat holes should be 15cm apart. It’s ideal for growing medium to large-sized onions inside the greenhouse onions bed.

Caring Tips for Growing Onions in Greenhouse

Onions are very easy to grow and they need very little or no attention. Like many vegetables, you want to keep your onions moist by watering them regularly – just take care to not overwater them – while any flower spikes that begin to grow should be gently removed.

Roughly towards the top of July, stop watering your onions so that they dry. This is often so that when the bulbs have swollen they need sufficient time to mature. For optimum results, it’s also an honest idea, at this point, to softly brush back the soil from the highest and neck to permit for optimum sunlight.

Onions are often vulnerable to the spread of diseases like bacterial and fungal spores, which may cause decay further down the road, especially if they need been overwatered or the greenhouse is especially moist. To stop this, gardeners should practice crop rotation to scale back the risks and may also stop spores from multiplying by spraying a fungicidal spray on the leaves weekly.

Common Pest and Diseases in Growing Onions in Greenhouse

Onion pests are listed below:

Like all other plants, onions will also prone to certain diseases and pests. Three pests that affect onion plants namely:

  • Onion root maggot fly

These flies have a humpback; lay their eggs at the rock bottom of onion plants, and therefore the fly’s larvae tunnel into onion roots. The flies emerge in late spring. These are controlled by a fine net or by introducing beneficial predator insect species to regulate it.

  • Slugs

They destroy the total surface of the onion plants. Surprisingly your next pest can kill them. You need to introduce beneficial bugs in the greenhouse to control them.

  • Onion Eelworms

They can cause significant bulb damage. They are called nematodes; they look like 1-2 mm long threadlike worms.

Onion diseases are listed below:

  • Downy Mildew/White rot

Is one among the kinds of oomycetes microbes that are termed obligate parasites of plants? It is often called onion rot. The disease starts to seem when it gets favourable conditions inside the greenhouse bed. Wetness and waterlogged areas help the spores to grow and damage the plant completely. The answer is to supply proper ventilation inside the greenhouse. Please don’t overlook this issue because if you probably did not attend now then ditch growing onions or any crop in your greenhouse bed for the subsequent 7 years.

  • Onion neck rot

The second main problem with onions is a fluffy grey growth on onion necks. That is called onion neck rot and it is caused by fungus.

Harvesting Onions in Greenhouse

You need to aim to harvest your green onions roughly 30 days from planting a group when the plants are at least 1 inch in diameter and 6 inches tall although this does depend upon the plant type or variety and your conditions. Once you have got harvested your onions, then you can leave them to dry out for around a week by spreading your onions out on a clean, dry surface and leave them in a well-ventilated yet dry location to fully dry the outer skins of the onions, prevent any mould from forming, and then allow them to ripen fully.



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