Photo: Pelargonium with yellowing leaves due to nutrient deficiency
I’m finding my untidy vegetable patch a delight this year.
I’m intentionally letting a lot of weeds and self-set plants grow in between
the rows and it really seems to be paying off keeping pests from the crops. I’m
happy enough to see most insects in the garden so it’s great to have somewhere
they can live happily without me having to try and get rid of them.
The last
time I noticed some cabbage white caterpillars, most of them were on self-set
rocket with just one rouge one on the new broccoli. Instead of resorting to
throwing the solo muncher into next doors garden I threw it over to his mates
so they can all munch on the tasty rocket together. It makes for a far less
barbaric gardening session when nothing needs to be killed, just rehomed. Apart from that one pest, the veggies have
been free of any P+D’s this year and I’ve found nasturtiums are another great
distraction for pests such as green and blackfly.
In Containers
I’ve used the neem oil for the first time this week. I
noticed that some of the petunias in containers and hanging basket plants were
infested with greenfly. The oil takes a bit of time to work, so hopefully the
plants will still be healthy after the pests have gone. Growing plants in
containers isn’t ideal and they can easily get stressed by drying out and
lacking in nutrients. Let’s have a look at what else stresses plants, these
will probably be relevant for houseplants too as these can sometimes suffer the
same fate.
Not all plant problems are caused by insects or diseases.
Sometimes an unhealthy plant is suffering from a nutrient deficiency or even
too much of any one nutrient. Plant nutrient deficiencies often manifest as
foliage discoloration or distortion. A lot of problems have similar symptoms
and sometimes it is a combination of a few things.
Be sure you eliminate
the obvious before you kill your plants with kindness.
- Check first for signs of insects or disease.
- Foliage discoloration and stunted plants can easily be caused by soil that is too wet and drains poorly or soil that is too compacted for good root growth.
- Extreme cold or heat will slow plant growth and effect flowering and fruit set.
- Too much fertilizer can result in salt injury. Your plants may look scorched or they may wilt, even when the soil is wet.
Plants require a mix of nutrients to remain healthy.
Nutrients that are needed in relatively large amounts are called the
macronutrients. Plant macronutrients include: nitrogen, potassium, phosphorus,
calcium, sulphur and magnesium.
There are a handful of additional nutrients that are
required for plant growth, but in much smaller quantities. These micronutrients
include: boron, copper, iron, manganese, molybdenum and zinc.
All of these nutrients are taken in through the roots. Water
transfers the nutrients from the soil to the plant roots.
So one requirement of sufficient plant nutrition is water. A
second requirement is the appropriate soil pH for the plant being grown. Each
plant prefers a specific pH range to be able to access the nutrients in the
soil. Some plants are fussier than others, but if the soil pH is too acidic or
alkaline, the plant will not be able to take in nutrients no matter how rich
your soil may be.
Plant Nutrient
Deficiency Symptoms
Macronutrients
Calcium (Ca) Symptoms: New leaves are distorted or hook
shaped. The growing tip may die.
Nitrogen (N) Symptoms: Older leaves, generally at the bottom
of the plant, will yellow. Remaining foliage is often light green. Stems may
also yellow and may become spindly. Growth slows.
Magnesium (Mg)
Symptoms: Slow growth and leaves turn pale yellow, sometimes just on the
outer edges. New growth may be yellow with dark spots.
Phosphorus (P)
Symptoms: Small leaves that may take on a reddish-purple tint. Leaf tips
can look burnt and older leaves become almost black. Reduced fruit or seed
production.
Potassium (K)
Symptoms: Older leaves may look scorched around the edges and/or wilted.
Interveinal chlorosis (yellowing between the leaf veins) develops.
Sulphur (S) Symptoms:
New growth turns pale yellow, older growth stays green. Stunts growth.
Solution
There will be a lot of companies recommending chemicals to
solve the issues but I have found rectifying these deficiencies can be easy
using a good quality mulch of well-rotted compost. Chemicals only feed the
plants and not the soil. It might be too late for some container plants so a
quick fix of comfrey or seaweed liquid might be required. The same goes for
micronutrients.
Micronutrients
Although only found in trace amounts, these elements can
make a big difference to the quality of the plant.
Boron (B) Symptoms: Poor stem and root growth.
Copper (Cu) Symptoms:
Stunted growth. Leaves can become limp, curl, or drop. Seed stalks also become
limp and bend over.
Manganese (Mn) Symptoms: Growth slows. Younger leaves turn
pale yellow, often starting between veins. May develop dark or dead spots.
Leaves, shoots and fruit diminished in size. Failure to bloom.
Molybdenum (Mo) Symptoms: Older leaves yellow, remaining
foliage turns light green. Leaves can become narrow and distorted.
Zinc (Zn) Symptoms: Yellowing between veins of new growth.
Terminal (end) leaves may form a rosette.
