When it comes to winter watering less is more
It’s easy to be tricked into thinking that plants showing signs of wilting foliage must need a drink
The majority of so-called plant diseases are really disorders aggravated or caused by stress. As temperatures drop and soils cool, most ornamental plants, including evergreens, take the hint and take a rest. During this period, little nutrition is required and watering reduced.
As winter approaches, many insect pests seem to disappear for a while. Some die after depositing over-wintering eggs while others form cocoons and go into winter dormancy. Plant disorders are different. Cool conditions during late autumn and winter often bring out a range of new ones.
The single biggest cause of houseplant death during winter is mollycoddling, especially through over-watering. It is easy to forget that these plants have virtually stopped growing. So damage is done when we thoughtlessly continue with summer habits by giving them daily drinks they cannot take up.
This is why winter potting soils often become so badly waterlogged they start to stink. This also indicates that soils are turning toxic.
Over-wet conditions cause normally friendly bacteria and soil fungi to go feral and start attacking plant roots. This is the real reason why over-indulged plants often look sick or collapse during winter.
Too often, problems of water-logged potting soil are made worse when more water is added. It’s easy to be tricked into thinking that plants showing signs of wilting foliage must need a drink. When extra fertilisers are also applied, it can lead to disaster. This is the equivalent of force-feeding someone dying from pneumonia with steak and kidney pudding.
Over-watering of pot plants can be avoided. Stick a finger into the soil every now and then. It’s a simple way of checking moisture levels. Potting soil in winter is best kept slightly moist, especially in cool districts. Drip trays beneath pots must never be allowed to remain filled
with water. That’s also asking for root-rot.
Most houseplants, especially cyclamens which have large, moisture-holding, bulb-like corms, or orchids with thick swollen roots, prefer soil to become almost dry between each watering.
In the garden the situation is different again. In cool districts, normal winter rainfall is enough to keep most plants happy, provided drainage is good. In heavy, clay soils, plants with shallow, compact roots such as rhododendrons, azaleas and some conifers need special care because waterlogging is always a winter danger. Conifers rarely show they are suffering wet-feet until it is too late. That’s when needles go brown and start to fall. All we can do is dig them out because few conifers can be revived after being seriously waterlogged.
Rhododendrons and azaleas give a clear warning when they are in strife. Should soil remain saturated where drainage is poor, leaf-edges take on a scorched appearance. This is marginal leaf-scorch and we must act quickly to save distressed plants. They are best lifted, dead roots scraped off, pruned lightly and replanted, this time into low mounds, even on the same spot. They are even safer if transplanted to new positions where drainage is good.
Just the same, signs of marginal leaf scorch can also be misleading. If these plants have recently endured a long, dry summer with limited water, many leaves show similar symptoms with leaf-tips dying back and going brown.
Chilly soils also cause nutritional deficiencies in many plants which show up in leaves. These mineral shortage symptoms can appear, even when soils are fertile. Low temperatures keep many mineral nutrients locked up and plants are unable to take them up.
Citrus trees such as lemons, cumquats and grapefruits often display pale or mottled leaves during winter. These are typical signs of nitrogen, iron, magnesium or zinc deficiencies, all elements needed by citruses. Foliar feeding, that is spraying leaves with a weak, mineral-rich nutriment at any time of the year provides good results. However, the real benefits come from residues that drip down over root-zones after folia feeding.