Nick's Garden: Time to feed and repot the plants

As summer draws to an end, a host of routine but essentional seasonal tasks await gardeners.
Fertiliser with phosphorus in it is good for blooming species such as Rangoon creeper because it encourages rapid growth and the production of flowers.
Fertiliser with phosphorus in it is good for blooming species such as Rangoon creeper because it encourages rapid growth and the production of flowers.

It's official. The summer is finally, thankfully, behind us. Now is the time to look ahead to the new season in all things: fashion, art, music, theatre and, of course, gardening.

I left the gelid, air-conditioned cocoon of my apartment today and, after many weeks, the sun brought a smile to my face. I was happy to finally be able to enjoy its warm embrace.

Poetry aside, there is a whole roster of relatively mundane but important seasonal gardening tasks to do now that the worst of the heat is past. Plants that have been dormant throughout the summer are starting to grow again and will need feeding.

For species that are racing and want to bloom, such as the Rangoon creeper (Quisqualis indica), the orange trumpet vine (Campsis radicans) and bougainvillaea, a fertiliser that is high in phosphorous is best because this mineral encourages rapid growth and the production of flowers.

Despite the differences in packaging, many feeds are a straightforward balance of the three macronutrients necessary for healthy plant growth - nitrogen, phosphorous and potassium - plus a small host of other micronutrients. If you are in any doubt as to what fertiliser is best, tomato plant food is always a safe bet because it is specifically designed to encourage the production of flowers and fruit and, mysteriously, always seems to be available even when other fertilisers are not.

Plants growing in containers will also need a pick-me-up after the summer's intensive irrigation, which will have leached most of the nutrients from their potting compost. Apply a top dressing of fresh compost by removing the top two to five centimetres of the old potting mix and replacing this with a fresh batch, mixed with about 10 per cent coarse sweet sand or an artificial material such as perlite or vermiculite, and lace the new mixture with slow-release fertiliser pellets.

If the leaves of your plants look sickly, pale and discoloured, it might be a sign of a nutritional disorder called iron chlorosis, a condition to which two of the UAE's most popular garden plants, citrus and gardenia, are particularly prone. Chlorosis can result from root damage caused by a lack of oxygen in overwatered or poorly drained soils, which is a particular problem for container gardeners, who struggle to keep their plants alive and end up almost killing them with kindness.

Iron chlorosis is easy to confuse with other nutrient deficiencies. If a plant is iron deficient, its newest leaves are more yellow than its old ones. If it's nitrogen deficient, the old leaves are yellow and the new ones are green. The easiest way to cure iron chlorosis is to apply iron chelate to the suffering specimen. Iron chelate is an organic compound that keeps iron soluble and available to a plant through its roots or leaves. Iron chelate is most commonly available as Sequestrene 138 Fe. This can be diluted and applied as a foliar spray or scattered as dry granules around a plant's drip line and watered in thoroughly so the chelate soaks into soil around its roots. Sickly leaves should start to green up in two to three weeks.

Some plants may require repotting, either because they have outgrown their current container or because of waterlogging. Roots emerging from the drainage holes at the bottom of a container are a sure sign that a plant needs rehousing. Another sign is when a pot drains almost immediately after the plant has been watered. Although the second symptom can result from compost that is so dry that it loses its ability to absorb water in the first place, it is also likely that the plant has become root-bound. In this situation, roots become so tightly packed that they displace the compost around them and there is not enough absorbent material in the root zone to retain water as it soaks through. This is most often a problem with very old plants and houseplants such as the Zanzibar gem (Zamioculcas zamiifolia), which develop thick roots or rhizomes.

While many pot-bound plants will be moved to new containers, it's possible to maintain the status quo by repotting a plant into the same container. This is a good option where custom-built planters are used or when variables such as the cost, age, size or aesthetics of a container dictate its continued use.

This type of repotting is far more risky. Plants have been known to die from shock, so I would only recommend it to more experienced gardeners. Prepare your plant the night before repotting by giving it a thorough watering and by pruning its stems. The following day, remove the plant from its pot and work your way over the root system, removing old compost and carefully teasing out and pruning roots so that the whole root ball is reduced by approximately five centimetres around its sides and bottom.

Once this is accomplished, repot the plant so that it sits several centimetres below the surface of the container, and refill the pot with moistened compost. Then irrigate carefully until water starts to appear from the bottom of the pot.

Allow the plant to dry out slightly before watering again. Keeping repotted plants in a shady, protected spot until they become established will give them the best chance of survival and success. Once they have started to show signs of strong growth, it should also be possible to take cuttings from them for propagation. If you take cuttings between now and the end of the year, new plants will have enough time to establish themselves before cooler weather arrives. They will also be large enough and sufficiently established by next summer to withstand the multiple challenges of drought and heat.


Ask Nick: You often mention the ghaf tree in your columns and talk about its drought-tolerance and slow growth. I have one in my garden that has grown from a small sapling to a large tree in only seven years. Can you explain this?

Like many drought tolerant plants, the ghaf (Prosopis cineraria) has had to adapt to life in extreme conditions. One of the reasons the ghaf can survive unaided in the desert is its deep tap root that burrows many metres through the sand to reach groundwater. In such conditions, its growth will be extremely slow and the plant that results will be stunted and contorted. However, if it is watered regularly it will respond positively and use as much water as it can. Unfortunately, the watered tree will not only look quite different, but it will also lack the hardiness of its desert neighbours.


Published: September 22, 2011 04:00 AM


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