Spring bulb tips

A guide to growing bulbs successfully

In warmer areas of New Zealand, bulbs may need refrigeration before planting. Most bulbs come from places which experience quite cold winters, and they need this cold period in order to complete the development of the flower bud. An insufficient cold period can result in no flowers at all. Bulbs should be put in the ground when the soil temperature is below 12C.

However, this is important as chilling incorrectly can cause as many problems as it solves.
  • Use a paper bag or an open container so the bulbs can breathe. Do not store in plastic bags as this will cause sweating and will cause mould and rot to develop.
  • Keep the bulbs to the side of the fridge, not at the back where they may ice up and, or where condensation may cause mould to develop.
  • Don’t keep fruit in the same fridge as bulbs as fruit, and include an ethylene absorbing sachet in with the bulbs to prevent ethylene damage and suppress mould.

Growing in the garden
All bulbs need to be grown in a well-drained but moist medium with a soil structure strong enough to anchor them. A loam-based soil is ideal but so few of us are blessed with this black gold so you may now have to add something to the soil to give your bulbs a greater chance of success. If you have a heavy soil, you will need to add grit (coarse pumice or sand) to help with drainage. Conversely if you have dry sandy soil or one that lacks nutrients you will need to add some organic matter to encourage water retention.

  1. Determine the planting depth for the type of bulb you’re planting. If planted too deep, flowers will bloom late or not at all. If planted too shallow, new growth may become exposed too soon and risk damage by cold temperatures. If you are unsure of the exact planting depth, a good general rule of thumb is to plant the bulb 2-3 times as deep as the bulb is tall, and 2-3 times their width.
  2. Place the bulbs with the pointy-end up and with the roots down. If you’re not sure of the top or bottom of the bulb, plant it on its side and it will find its way to the surface.
  3. Cover with soil and a light layer of mulch.
  4. Feed the plants when you first see stems appear, when they start to flower and once again when they begin to die down. The reason for feeding the bulbs when they begin to die down is to help with next seasons blooming as the bulb itself can store many of the nutrients for a healthy start.

Growing in pots and containers
As said before drainage is the key with bulbs, so all pots and containers need one or more holes in the bottom. These holes then need to be covered with gravel or pebbles to keep the holes from being clogged with earth.

Good soil is best but if you don’t have access to this then use a half and half mix of the very best potting mix and compost you can find. The better the growing medium the greater the chance of success.

Lay an inch of coarse or pumice or sand at the bottom of the pot- over the gravel, then the compost and potting mix or soil. Place the bulb with its pointy tip just below the surface and fill in around it.

If planting just one layer of bulbs, plant at the same depth as you would in the garden. At a depth of twice their height.

In pots you can plant your bulbs closer than you do in the garden however they shouldn’t touch each other or the sides of the pot.

Water on planting and regularly in the first weeks when their roots are forming.

Growing bulbs indoors
Most bulbs for forcing indoors need 10 to 15 weeks in the cold to flower well. Ideally, keep them at a temperature between 1.5C and 10C (at a pinch, 12.5C) in a cupboard, shed or garage or fridge. This cold period makes the bulb think it is winter, stimulating a biochemical response to make it start flowering. Amaryllis are the exception and do not require a cold spell.

Once they've had their cool period, you can bring them in somewhere warmer, above 15C and they will quickly sprout, then bloom. As far as they are concerned, spring has arrived.

Most bulbs also need a period in the dark, to give the root time to develop before the light pulls the flower and leaves from the bulb. Again, Amaryllis is an exception, as is Freesia and Tazetta Narcissi, but for most, the dark spell is as essential as the cold one.