The art of growing bulbs in greenhouses

A bulb is a bulb is a bulb, right?

While bulbs tend to be grouped together under a generic label, there are actually four distinct types.

• True bulbs

These have a central stem or shoot surrounded by several fleshy layers that store food. Examples of true bulbs include onions, garlic, daffodils, tulips and amaryllis.

• Corms

From the outside, corms closely resemble true bulbs. The difference lies on the inside, which is solid rather than layered. Gladiolus, crocus and freesia are all corms.

• Tubers

Tubers are thickened stems – or in the case of dahlias, thickened roots – which have buds or ‘eyes’ that sprout stems and flowers. Daylilies and cyclamen are popular tuber varieties.

• Rhizomes

These are underground stems that store food for the plant and are able to generate new growth. One of the best known rhizomes is the Iris.

So, how do bulbs start life and what role does a greenhouse play in their growth? Let’s dig a little deeper into the journey from seed to bulb and flower to find out.

The lifecycle of a bulb

At the start of the cycle, imported seeds are sown, which result in mother bulbs. These are then multiplied and harvested – most bulbs produce around 5–6 young bulbs – and sold to farmers around the world. With bulb varieties that produce only one or two bulbs, a tissue culture is performed in a laboratory so that their yield is greater. Once the bulbs are ready for germination, they are placed in a greenhouse equipped with the necessary systems to create an optimal environment.

Heating

In the case of Amaryllis bulbs, maintaining a constant temperature of 20°C for the first 14 days, followed by a temperature of between 24°C and 26°C, is critical to growing success. If the temperature is too low (below 20°C), plant growth is negatively impacted. Too high (over 30°C) and the plant becomes stressed. 

Ventilation

Amaryllis also need a well ventilated environment to flourish – one where the relative humidity of the air remains as low as possible. The greenhouse where the bulbs are germinated must be tailored to meet these exact requirements. 

Irrigation

Bulbs have very specific water requirements and ensuring that they receive just the right amount is crucial to successful growth. While bulbs should be thoroughly watered after planting, it’s important that they’re not watered for the next week – leaving the growing medium to dry allows new roots to form. It’s also vital that the bulbs are not over-watered as this can cause the roots to deteriorate. A greenhouse fitted with a drip irrigation system ensures that bulbs receive only as much water as they need, when they need it.

Planning a greenhouse nursery project?

Vegtech Netafim has extensive experience in designing and constructing hi-tech greenhouse nurseries. If you’re planning a greenhouse nursery project and need a partner who will understand your needs – and deliver real results for your business – get in touch today.