Dealing with Plant Disorders: Non-nutritional Disorders Part 1
By Steve Malsher MCIHort
Following on from our look at nutritional disorders in last week’s blog, Steve now identifies some of the non-nutritional plant disorders that we should be looking out for in our garden.
Disorders are plant problems that are caused by a problem within the environment in which the plant is being grown. They are often called Plant Physiological Disorders and they tend to be of two types: those caused by nutritional disorders and those caused by non-nutritional disorders.
Non-nutritional disorders include:
Who got caught out this year by the two late frosts in May? In my lessons, I heard stories from students who had moved tender plants out and had a catastrophe with them. Yew, Beech and Parrotia suffered, as they started flushing new growth after a warm spring. It is considered in Oxfordshire that the last frost occurs around May 15th, so keep your tender plants inside until after that date.
Frost can affect many plants, and is particularly damaging to tender new growth and blossom in the spring. Damage is seen by the blackening of parts of the plant, particularly on new growth. Shoots may be scorched at the tips and flowers can be killed outright. The damage is caused by the formation of ice crystals in the plant tissue that pierces the plant cell walls.
Ground frost occurs when the temperature falls below freezing point and air frost occurs when the temperature of the air falls below freezing point. Repeated freezing and thawing, or very rapid thawing, can be particularly damaging to plants.
Once the temperature has fallen below freezing, a strong wind can make frost more damaging (wind chill). Cold winds remove moisture from evergreen foliage more quickly than it can be replenished by the roots, which can cause leaf browning, particularly at the tips and margins.
Tender plants survive the winter better when they are planted in a sheltered sunny position. This is because new wood is ripened by the sun, accumulating more carbohydrates during the growing season, making it more frost resistant.
- Choosing hardy plants (or those that flower as late as possible).
- Avoid planting in frost pockets (or allow the frost to escape if possible).
- Cover plants with protection, such as horticultural fleece, or cloches.
- Mulch the root area of evergreens, conifers, tender shrubs and tender perennials with a thick layer of organic matter to prevent the root zone from becoming frozen.
- Move containers to shelter or indoors during frosty periods.
Water is necessary for all plant growth. Plants with large, smooth leaves – especially vegetables – are particularly vulnerable. The shortage may be from insufficient rainfall, poor water retention of the soil, or a drying atmosphere from either wind or high temperature.
The condition can be seen as a general dullness of the leaves, followed by wilting. As the condition continues, the leaves gradually turn brown and may drop off. Some plants ‘bolt’ and run to seed, meaning they cease flowering as seeds develop. For example, onions and lettuce.
Parts of the plant furthest from the root are usually affected first and most severely. Newly planted climbers, shrubs and especially trees are at extra risk because their root system takes several years to develop to the point they are drought-proof.
The problem can be tackled by:-
- Choosing drought-tolerant plants.
- The incorporation of plenty of well-rotted organic material (WROM).
- Mulching to a suitable depth to prevent evaporation.
- Irrigation systems being used correctly
- Hand watering.
As a rule of thumb for herbaceous beds I like to give the equivalent of 25mm of rain per week and I would apply this in two watering sessions. It is better to give a really good soak twice a week than a sprinkling every day. The reason for this is that the water gets further into the ground forcing the roots to follow the water and losing less by evaporation. If you have an irrigation system, Nicholsons have staff that can make calculations and set timers to ensure yours is operating to its maximum potential.
Trees – If you have a newly planted tree, we recommend that you give it the equivalent litres of water per week, that matches the pot size in which the tree was contained.
Flattened, elongated shoots and flower heads that look like many stems compressed together are called fasciation. It is produced by abnormal activity in the growth of the plant. Whilst the flowers or stems may be deformed, normal growth stems can still appear.
Symptoms include :
- Flattened shoots
- Shoots that appear to be made up of several fused stems.
- Flattened elongated or misshapen flower heads with numerous flowers.
It is caused by various things including a random genetic mutation or disruption of the plant’s cells, a bacterial or viral infection, or sometimes caused by damage from frost, animals, chemical or mechanical injury.
There is no control apart from pruning out stems and flowers if desired, but it does not appear to cause any long-term damage to the plant.
Although this can occur with indoor plants and outdoor plants it tends to be seen more frequently indoors. It is probably the commonest cause of the decline of house plants. That said there are many plants outdoors that do not like wet conditions, Yew and Beech specifically.
Waterlogging causes lack of oxygen to the roots and the inability of Carbon Dioxide to diffuse away from the roots. It can be identified by wilting of the leaves and general stunted growth. The plant will often wilt and can appear to be suffering drought stress, which many people confuse with a lack of water, hence compounding the problem.
Outdoors the soil needs to be improved by adding well-rotted organic material, or horticultural grit. In severe cases especially in clay soils, drainage systems are sometimes necessary.
Bottle bottom planting can be employed to raise a rootball with grit being added to the planting pit (so-called as the mound created resembles the curved underside of a bottle).
House plants should be carefully monitored to ensure they are given neither too much or too little, the pot can be placed in a saucer.