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Bulbs: How to keep them healthy by Malcolm Campbell

Bulbs are not generally afflicted with lots of diseases or insect pest vectors. They grow rapidly flower, then die down and in doing so conserve their resources, concealing them from most insects. In common with many plants, pests and diseases effect your plants when the plants are being grown too softly. That is with too much water or fertilizer. Since bulbs sneak up on us and frequently get left in the ground and dare I say, get overlooked, they don't get spoilt like many other more conspicuous plants. When they burst into flower it's already too late to fertilize them. In most cases that flower formed within the bulb, tuber or corm in a previous season, so any fertiliser added usually only effects next year's crop.

That highlights the need to buy big healthy sound bulbs. There is no such thing as a cheap bulb. You get what you pay for. The competition between bulb growers and sellers is fierce and with most bulbs being sold through national mail order houses, the price they are sold for is a national issue, so the chances of getting quality bulbs for a discount price, is remote.

You get cheap bulbs if they are small for their type or if there is a chance that they are not as sound as many in the market place. Liliums in particular are a can of worms. They can vary enormously in size and of course size determines how big a flower you will get in the first season, as it does with hyacinths, daffodils, tulips etc. Small hyacinth bulbs for instance will not flower in their first year since they are offsets and require at least two, sometimes three years before the bulb is large and mature enough to flower. Bulb growers have a few tricks to force some crops along and even produce exceptionally large bulbs that flower with huge flowers in their first year, but unless you are as skilled, your second year flower will be a much more modest specimen. Try growing 'Monet' Tulips and your will see what I mean. They are exceptionally large bulbs that make plants of 70cm tall with mammoth flowers in spring, but even if you feed them after flowering and lift them to store in summer, your second year flowers will be much smaller. That's because in most areas where they will be sold, the conditions are less ideal than in the lovely Dandenong Mountains where they were grown, fertilised and nurtured. Those 'Monet' Tulips are worth paying the extra for. Every year in fact. The easiest way to avoid disease in the bulb garden is to rotate crops and buy a large part of your collection fresh every year. That might sound incredibly extravagant, but if you have a feature bed for bulbs, buy quality large fresh bulbs every year and you will amaze yourself.

It is important to provide ideal storage conditions for your lifted bulbs, tubers and corms too and the ideal is seldom a hot corrugated iron garage. Use the red net bags that are available from your green grocer and hang them in a dark spot that gets some air moving by them. Such a spot could even be indoors. I know of keen seed collectors who store their seed suspended from under their bed, since that room has the most constant and even temperature and humidity.

Planting at the correct depth for the bulb is also critical to the general health of the plant. On sandy soils you can generally plant deeper than is recommended and similarly shallower on heavier soils, produces good results. For container grown bulbs always use a free-draining open potting mixture, deep containers and mulch the surface to reduce disturbance when watering. Many of the taller tulips and Alstroemerias need staking to support their heavy canopies and provide an open habit for their foliage. Failure to do so will see the foliage rot and disease spread. Link stakes are ideal or simple runs of light wire suspended by stakes at each end, which is the way commercial carnation growers support their crop and make picking easier.


Studying the natural habitat of some bulbs can be a really great way to get a good crop especially if it happens to be an unusual variety you aim to grow. I tried growing the native Callostemma for some years, unsuccessfully until I took more note of their natural habitat, then they thrived. The tulip species grow naturally in some of the most inhospitable environments in central and western Asia and so if you want to grow Tulipa greigii don't pamper it. Plant it amongst a rock outcrop in full sun!

If you are growing a bulb that needs feeding, the rule of thumb is to feed it with water soluble fertiliser after flowering and then let it die down. The exceptions are those Crinum and Clivia cultivars that are fed during their warm wet growing season and seldom die down afterwards. Many bulbs have surprisingly poor nutrient requirements and if growing in a rich garden soil may thrive for many years without fertilising. I'm always amazed to see patches of naturalised bulbs on a roadside in the most desolate conditions. A small patch of Scilla at Lenswood in the Adelaide Hills has astonished me for years, but on close examination it's a pool of water on the kerbside just below its bulbs, that nurture it. I hope they never grade it away!

If you have low lying areas where water can lie for a while after a heavy down pour or during winter, avoid planting any bulbs there until the drainage has been improved. Do that by installing slotted agricultural pipes down the slope or by spreading gypsum at the rate of 300 grams per square metre over the surface and if that doesn't improve the drainage within a week then add another dose of gypsum. If that doesn't work, start digging. Most bulbs need a well drained soil to thrive. When planting bulbs in heavy loam, it's advisable to sprinkle some sharp sand into the planting hole just so that there is a barrier between the loam and the bulb and never put compost into the planting hole! The decaying organic material is a sure-fire way to introduce some sort of fungal rot. Organic material for bulbs is usually added as a mulch on the surface, to rot down during the growing season and not dug into the soil.

You will read of Narcissus Basal Rot in bulb books as a disease of daffodils and their related friends, but with sound bulbs and good drainage you will never see it. Very keen daffodil growers have been able to fumigate their exhibition stands of daffs every autumn with deadly Methyl Bromide gas, laced with Chloropicrin. That's the Mustard gas used in the trenches in France in 1916 and that very same gas, is no longer available to home gardeners and is rapidly being phased out for profession growers too. Commercial growers may have to rely more on phosphine. For the home gardener the best alternative is still good drainage and healthy bulbs. If when you are lifting your bulbs at any stage, you detect a bulb that is decaying, then remove it and don't add it to the compost heap!

A remedy for fungal diseases that you may have read in some old garden books advocates dipping your Gladiolus corms in Mercuric Oxide. Don't spend too much time trying to find that either! It's pretty toxic and not to be recommended. There are other dips available and also a host of systemic insecticides that provide some resistance to your Gladies in particular, as they grow, since they are most regularly infested with Thrips. You might control Thrips by attracting them to a few target Gladiolus plants by spraying a sugary compound onto the leaves. The Thrips then colonise a few plants, leaving the bulk relatively free from infestation and the tell-tail streaks on their leaves and spots on the flowers. You can then use a knock-em-out contact insecticide or suffer the consequences of neglect. In common with most Rose growers, Glady growers learn to live with regular applications of insecticide sprays. The systemic insecticides come in granular form too, such as Bayer's Disyston 50®. A measure can be inserted into the planting hole as they are transplanted to give six week's protection or spread as a top dressing in the growing season. The latter needs some extra attention if you have foraging pets, because in common with all insecticides organic and chemical, they are toxic. It's a fallacy to think that if an insecticide is made from organic or naturally occurring compounds that it will be safe to use. If it was safe to humans then it wouldn't kill insects! Some organic compounds such as those derived from Saponins, are more toxic than many chemical compounds sold for home garden use. They all require protective equipment and should be used according to the precautions and quantities on the label.

A few conspicuous pests are ants and aphids. Thrips being less obvious to the untrained eye. Ants don't feed on healthy plants, but they milk the scale and aphids that graze on some bulbs and shrubs for a sweet secretion. Eliminate the aphids and scale or any other obvious vector and the ants will disappear too. Earwigs can damage flowers and foliage too and in mild spring season they breed up in very large numbers. Last spring in Adelaide was very mild and they went amok. They are very active at night and can be trapped rather then sprayed. A margarine container half-full of old cooking oil sunk into the ground, provides a lure and a sticky trap from which they cannot escape. They drown and can be sieved off each morning by the handful, so that the oil can be recycled! The variety of cooking oil is irrelevant. I've had people recommend to me the use of rolled up cardboard core-flute packaging hidden amongst the plants and the earwigs hide in the cavities at dawn. You then squash the core-flute material and with it the earwigs. The oil works a treat and it's always hard to find a use for very old cooking oil or sardine oil anyhow.

I've avoided a long analysis of various bulb diseases principally because it's very difficult for the average home gardener to identify the problem anyhow and by the time it manifests itself, it's too late. Positive identification is only really an option if you are growing a single crop, where you can isolate the disease. If you are a keen grower of a single crop, Salinger's book is an excellent reference and will save you a fortune. It is the best in print for our region, although at $60.00 it's definitely for the bulb aficionado.

Whether you spend a few dollars a year or a small fortune, most southern gardeners can improve their drainage for better results. The good news is that even with above average neglect most bulbs thrive!

Further reading
Commercial Flower Growing, by John P. Salinger, published by Butterworths (NZ) Horticultural Books, 1985, 269 pages softcover, Black and white illustrations, rrp $60.00., by John P. Salinger, published by Butterworths (NZ) Horticultural Books, 1985, 269 pages softcover, Black and white illustrations, rrp $60.00.

Gardening Down-under, by Kevin Handreck, a CSIRO publication, 1993, 181 pages softcover, colour illustrated, rrp $****. The second chapter on soils and how to use gypsum, makes this a great investment for bulb growers., by Kevin Handreck, a CSIRO publication, 1993, 181 pages softcover, colour illustrated, rrp $****. The second chapter on soils and how to use gypsum, makes this a great investment for bulb growers.

Growing Bulbs, by A.G.W. Simpson, Kangaroo Press PO Box 75 Kenthurst NSW 2154, 1985, 88 pages softcover with colour plates rrp $14.95., by A.G.W. Simpson, Kangaroo Press PO Box 75 Kenthurst NSW 2154, 1985, 88 pages softcover with colour plates rrp $14.95.