Have you ever seen damage similar to the photo on the left in your lilies? Were you worried or wondering what might have caused it? Speckled yellow, wilted foliage at the leaf tips, turning to brown in some cases, but in almost every case the damaged area remained pliable rather than becoming dry and brittle. Another curiosity to me was the fact that the damage was not seen from stem to tip in most cases. Sometimes it was from the tip down only a few cm, other cases it was extensive, covering up to 30 cm of stem. Often it was found in the middle of the stem with no visible damage above or below that point. In most cases, the plant continued to grow and appeared to flower normally.
My first thoughts were that the damage was caused by a frost I had somehow missed as it seemed only lilies that sprouted up early were affected, including one variety of Martagon. At our location, spring arrived early (the year I first saw this), followed by a spell of cooler than normal weather, but no frost since the first week of April that I knew of. Lilies were sprouting by the first week of April, then sat and did nothing for a few weeks as the weather stayed unseasonably cool and cloudy. I also considered botrytis and herbicide damage as causes but these didn’t quite fit well enough to satisfy me.
As a greenhouse grower, I had seen similar damage, particularly potted plants including lilies grown indoors but never had I seen the damage to the extent I saw it in the Spring of 2006 on lilies growing in the ground. We also saw it sporadically on the second planting of lilies we potted, but not one incidence in the first planting done one month earlier. In the greenhouse, the damage would have been easily recognizable as Leaf Scorch typically seen after a spell of cool cloudy days immediately followed by clear, bright sunny weather.
By the end of May, similar damage had been described to me by a number of gardeners and my curiosity as to the cause was quite strong. I suspected it was environment and/or weather related and my suspicions were confirmed later in the year when I had time to do some research. I found out it was indeed environmental, or as a scientist might call it physiological damage. I also found out it was quite common in greenhouse grown lilies and that certain varieties are more susceptible. It did turn out to be Leaf Scorch, I was gratified to learn I was on the right track! Contributing factors to causing the symptoms include rapid root growth under warm conditions in wet soil or bulbs grown in cold, compacted wet soils with slow root growth. Seldom fatal to the plant but damage should still be controlled where possible as other problems such as Stump Rot or Botrytis (as seen in the photo below) are secondary to the initial damage on susceptible varieties but certainly not on all.
Surprisingly, I also learned that deficiencies in calcium and excessive amounts of fluoride in the soil can also cause this, the typical reason in greenhouse grown lilies. Calcium is vital for stem strength. In rapidly growing foliage, calcium transport to the leaf may be restricted by high humidity levels that slow the rate of transpiration. Since calcium is carried by the flow of transpiration, a slower rate of transpiration means less calcium reaching leaf tips. Low calcium levels in the young expanding foliage can induce tip burn and contribute to leaf scorch. Promoting air movement across the plant leaves will help push up transpiration rates and the transport of calcium from the plant roots up to the leaf tips. Flouride is a natural ingredient in superphospate, which is often in potting mixes and commercial fertilizers. Perlite, a common additive in potting mixes also contains modest levels of fluoride, enough to cause the damage in lilies. This explains why the symptoms are seen more on potted plants than in the ground.
So what can we do about it? While there is not much anyone can do to control the temperature of soil or air in garden grown lilies, there are other things we can do to minimize this type of unsightly damage to our prized lily stems when Mother Nature persists in sending us unfavourable weather. Good growing practices call for planting lilies in a full sun, open area and in loose, well-drained, nutrient balanced soil. Maintaining pH in the soil at 6.5 can help as will crushed eggshells mixed into the soil to supply calcium as the shells disintegrate, or you can add calcium-high lime. Side dressing plants with bonemeal increases calcium in the soil. Also, you may add powdered milk - which contains calcium - to your watering can and water around the stems. Commercial sprays of calcium nitrate meant for plants are available as well – any spray which says it treats blossom end-rot in tomatoes will help. A spray of 1 tablespoon of Epsom Salts to 1 gallon of water will boost the magnesium levels and improve the plant ability to absorb the available calcium. Do not use Perlite in your lily garden or in your potted lilies, instead use calcined clay or zeolyte to loosen and provide adequate drainage where needed. Or, you can choose to do nothing at all, knowing it is not fatal and not likely to be seen again unless the same conditions persist.