Bulb Growing Guide


Planting Hints & Suggestions


Planting Period

Bulbs and Perennials should always be planted when they are dormant.

  • For Spring Flowering Bulbs, plant in Autumn
  • For Summer Flowering bulbs and Perennials, plant in Winter-Spring

Planting Depth & Spacing

As a rule of thumb, the bulb should be planted twice as deep as the height of the bulb. Perennial plants should have their root system placed beneath the surface of the soil, with the crown at soil surface level. Loosen the soil well, then dig a trough to the length and depth needed. Level the soil at the bottom of the trough before planting the bulbs at the proper intervals-large bulbs at approx. 12 cm apart, and smaller bulbs at approx. 10cm. Most Perennials should be planted approx. 20cm to 45cm apart, depending on flowering size and height. Cover the bulbs with the loosened soil and water immediately to allow the bulbs to start growing. In the event of severe frost, cover with a layer of peat or leaves. This keeps the soil from drying out.

Soil Types & Requirements

Bulbs grow best in good quality, well-drained, fertile soil (although they WILL tolerate a lot less.) A pH of anywhere between 5.5 and 7 is ideal for bulbs (almost NEUTRAL, being neither acidic nor alkaline.) If your soil is too acidic, dig in some LIME, which will raise the pH. If your soil is alkaline, add some SULPHUR. If you are having difficulties growing many different types of plants successfully, we suggest a purchase of a soil-testing kit or meter. MOST garden plants require a pH of 5.5 to 7.

Sandy Soils: Although being infertile, sandy soil has free-draining qualities (which bulbs enjoy), and is easy to dig and work with. The main work with this soil is the continuous need to work in a lot of well rotted manure or compost to improve its fertility, and the mulching with well-rotted organic matter, as previous applications are used up quickly, or washed through the soil. Most garden soils however are perfectly adequate, needing nothing more than regular applications of rotted organic matter or a Complete Fertiliser, or specific bulb food.

Drainage

Well-drained soil is of prime importance ... most bulbs will rot in soil that stays sodden, and this naturally occurs more so when the bulbs are dormant. Drainage can be improved easily by digging in a lot of sand, or by raising garden beds.

Fertilising

Soil structure and friability can be greatly improved by digging it over deeply and incorporating very well rotted manure or compost, or some Complete Fertiliser. Avoid the contact of fertiliser with the bulbs as emerging roots will burn.

Naturalising Bulbs in Lawns

Cut out a rectangle of turf with a sharp spade and roll it back like a rug. Dig out the exposed soil to a depth much greater than the planting depth of the bulbs. Back fill to the right depth with a mixture of the excavated soil and rotted organic matter (or use a Complete Fertiliser). Place the bulbs in a random group and cover with more of the soil/organic matter mix, until the original soil level is reached. Tramp down and water well, adding more soil if there is slumping. Re-lay the grass and water again. Mow the grass for the last time as soon as you see the first sign of a shoot. When many shoots are visible, feed the area (top-dress) with a complete plant food, or specific bulb food.

Planting Bulbs Under Trees

Bulbs should not be planted under trees! Tree roots take an enormous amount of nutrients and moisture out of the soil, leaving little or nothing for bulbs. In addition, unless the trees are deciduous, the area under trees for spring flowering bulbs can prove too shady for successful results with bulb flowering. The best conditions for planting under trees are to choose deciduous trees only, and to build the soil up to at least 12 inches, and fertilise well, in order to provide nutrients for the bulbs, away from the demands of the tree roots. The best choices in spring bulbs are Bluebells, Daffodils and Crocus. (Perhaps some very lightly foliaged evergreen trees may be suitable, which only provide very light, dappled shade.) Lily of the Valley, Agapanthus, Crinum, Clivia are ideal choices for summer.

Planting Bulbs In Pots

Choose either plastic, metal, glazed ceramic or terracotta pots, with large drainage holes. Terracotta pots are porous and lose water through their sides and drainage holes, and will require more watering and feeding, as watering washes nutrients out of the potting mix. The other pots are waterproof and dry out relatively slowly. Use a light soil. Combine equal parts of weed-free garden or potting soil, peat and sand. Mix through some Complete Fertiliser, avoiding contact with bulbs. Planting bulbs outdoors in pots in this way will provide for brilliant Summer colour. Plant as follows:

  • Place a piece of broken clay pot or a few flat stones over the drainage hole to prevent clogging and stop the soil form flowing out. Fill the pot half full.
  • Place bulbs on top of soil with their tips just below the pot rim. Avoid pressing the bulbs into the soil, it can damage the bulbs base, and hinder root growth.
  • Add the remaining soil; stop when the tips of the bulbs are still visible. Label each container and note the variety, colour, date of planting and date for removal from storage.
  • Water well, either from the top, or immerse the pot in a pan of water, until all the soil is moist. Once only. Water once weekly only if low rainfalls.
Bulbs are in danger of "cooking" and failing to flower if pots are left in the full sun, and absorb too much heat. The potting mix dries out too quickly and subsequently bulbs overheat. This can be avoided by placing the pot inside another larger pot or cane basket to break down the concentrated beat. Place pots outdoors, protected from strong winds and frosts, in a position where they will receive natural rainfalls as much as possible. Bring pots indoors to enjoy when flowering begins. When flowering has finished, plant pot in the garden until next Autumn, then lift and replant.


Bulb Maintanance


When to Tidy Up

Summer bulbs and perennials are normally pruned back in May-June when frosts affect them. With evergreen varieties, simply prune back dead flower stems. All others, prune back to ground level.

Watering

As bulbs store water in their natural make up, they require little additional watering. Water bulbs once at planting, and if you enjoy regular natural rainfalls, NO FURTHER WATERING IS REQUIRED! If you experience LOW rainfalls, water bulbs ONCE WEEKLY ONLY! Many bulbs can tolerate even less watering and are therefore ideal for dry areas. Some of these drought tolerate bulbs include: Daffodils, Arum Lilies, Belladonna, Crinum, Dutch Iris, Freesias, Ixias, Nerines, Ornithogalum, Queen Fabiola, Sparaxis, Spring Star, Tritonia, Kniphofia, Gazanias, Violets.

Forcing

Coaxing spring bulbs to flower in winter is done by deceptive use of light and temperature, causing the bulb to believe that in a period of 12-15 weeks it has experienced a total winter-spring span of 5 months. The potted bulbs must be placed in an indoor storage place where the temperature will stay between 5-10°C (in a cool cellar, or old refrigerator, garage or outdoor shed). Pots rooted indoors must be kept in complete darkness and watered regularly. As in outdoor potting, choose pots of any type with dramatic holes and use light soil.

The potted bulbs now need a period of cold storage (ie of approx. 12 weeks to develop roots, stem and bud.) Bulbs can also be rooted outdoors by placing the pots in a trench out in cold soil, deep enough to hold the pots and 3 inches of sand. Spread an inch of sand or pebbles on the bed bottom for drainage. Set the pots, and cover them with 2 inches of sand and a mound of about six inches of soil. Dig a small trench around the bed for water run-off. Water the bed regularly to keep the potting mix evenly and lightly moist not sodden and not dry. Apply a mulch of straw, hay or evergreen branches etc. for protection.

After a minimum 12 weeks, the bulb will have adequate root and sprout growth with roots visible through the drainage hole and sprouts will be one to three inches tall. Now the containers can be placed in a warmer environment; place pots in an 18°C semi-dark area. After 4 days transfer to a well lighted 20°C area for flowers to bloom. Water regularly and keep pots away from heater and draughts. Warmer temperatures will shorten their bloom; place in sunlight by day, and move to cooler locations at night.

Bulb Chilling

Spring flowering bulbs only require refrigeration if being planted in warm climates, in warm soil, which does not cool down, e.g. QLD, NT, and areas of WA, and northern NSW. Cooler climates such as VIC, NSW and TAS provide cool soil conditions in March-April, and this is the ideal time for planting spring bulbs. Tulips should be the last to be planted, in April rather than March. The rule of thumb for refrigeration for spring bulbs, is to place bulbs in the crisper, away from fruit and vegetables, for 6 weeks at 5 degrees. Bulbs should then be planted in cool soil; if in doubt, place bulbs into pots, and place in the shadiest, coolest area of the garden. Summer flowering bulbs and perennials require no chilling.


Bulbs That Will Not Flower...


There are causes, other than pests and diseases as to why bulbs may not flower.

  • Bulbs are planted too deeply » Replant.
  • Immature bulbs, which havent yet reached flowering stage » have patience.
  • Excessive application of fertiliser (particulary nitrogen fertilisers) » Refrain from further application until excess is leached out the the soil.
  • Compacted soil » Dig up and add coarse sand, gypsum, well-rotted compost to help break up the soil.
  • Climate to cold » Possibly grow in a greenhouse, or re-plant the bulbs in a more sheltered position.
  • Climate to hot » Re-plant the bulbs in a more shady position.
  • Overcrowding - Bulbs are "blind" and produce only foliage » Separate clumps and replant.
  • Unsuitable bulb storage » Store Spring flowering bulbs in a well ventilated, dry and warm (less than 25°C) environment. Store Summer/Autumn flowering bulbs in a cool and dry environment.
  • Generally poor growing conditions » Too shady, too sunny, too many invasive roots from other plants, soil to wet, soil to dry.