A Glimpse Into The Future

Ornamental horticulture covers a vast range of crops and each requires different growing regimes, but all need nutrients in one form or another. How those nutrients are provided, the changes that have occurred in the past, and forecasting the future is the basis of this article.

In the distant past when container growing became popular, loam-based growing media was used – usually of clay origin – which contained lots of trace elements, so all that was needed was the addition of nitrogen, phosphorus, potassium and possibly a bit of lime. These would all come from straight fertilizers which tended to be soluble in water. If not taken up by the plant they would be washed out and needed replacing at regular intervals. This was either done as liquid feeds from an own mix of water soluble fertilizers, or as a top dressing.

With changes in growing media from loam to peat, peat reduced, or even peat free, the fertilizer also needs to be changed. The basics remain the same but the ratio of nutrients and the means of getting the fertilizer to the plant has altered. Most growers buy in ready-mixed compost and often want the fertilizer to last the life of the crop so that they only need to water. Crops are in the nursery for different lengths of time, so each has varying requirements

Nursery Stock
In the UK the number of plant species grown in a nursery is quite considerable and the requirements in terms of compost mixes is kept to a minimum in order to keep things simple. Things have moved on from straight fertilisers to controlled release fertilizers. These release nutrients at a rate that changes according to the temperature. This follows the rule that higher temperatures mean more sunshine, more photosynthesis, more plant growth and consequently a greater demand for fertilizer. 

The standard would be a CNS general compost with 4.5kg/m3 of a 12-14 month controlled release fertilizer. This has to be a compromise and some species will have too much and others too little, and as a result quality suffers. However, there are controlled release fertilizers that will mimic the growth pattern of different types of plants. Low start fertilizers encourage rooting and then release more as the season progresses. This is ideal for early-planted conifers and also for autumn-planted crops which do not want to be too soft in the back end of the year.

There are also high-start products which will suit deciduous crops that put on a lot of growth in the early part of the season and ease up during flowering and seeding. This type is also very useful for late-planted conifers which are already in growth and requiring instant nutrients. Some exciting new developments are being made in controlled release fertilizers. One such product is Osmocote Protect, that has a dual coating which stops release of nutrients for the first couple of months while the first coating breaks down and then releases as normal. This means crops can be potted on out of season during the winter months without the loss of fertilizer due to the elements. The fertilizer then kicks in during the spring.

In addition, there are products that contain a proportion of dual-coated granules. This means that nutrients can be targeted at different periods of growth. At present these are NPK nutrients, but with this technology specific elements like potassium could be supplied to the plant during flowering. The potential is endless. It does however mean growers have to be more aware of the way particular species grow and utilise the most appropriate fertilizer for the job.

Apart from conventional fertilizers there are many trends in the use of biological elements and natural complex molecules. Compost tea is quite widely used, which provides a combination of both. Mycorrhiza and some bacteria compete for the same nutrients as pathogens and therefore restrict the spread of disease. On top of this they can work synergistically with roots to aid nutrient uptake. The complex organic molecules like amines and proteins can be beneficial to plants. Many of these things seem to work best when the plant is under stress and therefore can appear to only work sometimes.

Compost tea also contains some nutrients. Many growers are using sub optimal controlled release fertilizer rates, and there is inevitably more growth seen when this product is applied. None of the biologicals are new, but there is a lot of research being done to develop better strains. As these become available fertilizer types may have to be reviewed.

Herbaceous
Herbaceous plants tend to be soft, leafy and grow fairly quickly. The normal recommendation for these crops is again controlled release fertilizer. Normally an 8-9 month longevity is ideal with a high potassium to nitrogen ratio. This provides good leaf colour and compact growth. If compost is made of materials having a high potassium level, then a balanced controlled release fertilizer would be more valuable. Many of these plants appear improved when extra iron is provided. This sounds obvious, but many areas have hard water which can lock up iron very quickly. Some controlled release fertilizers are more efficient at releasing iron than others and many use a proportion of chelated iron which protects the iron until the plant can take it up.

Pot Plants
The aim of producing a good pot plant is to control its growth to maintain leaf colour, and ensure it’s bushy, with lots of buds and reasonably compact. This is normally done with a combination of fertilizer and growth hormones. The latter is a costly process which can cause distortion and scorch if it isn’t applied at the correct rate and time. Too much can also stop the plant growing altogether which is disastrous for a market dictating a particular size.

Controlling plant size with fertilizer can reduce the growth hormone usage. It is still quite a skill as there is always a delayed response to fertilizer change, so anticipation is the key to success. Pot plants can be grown with either controlled release or water soluble fertilizer. Preferably a combination of both should be used to ensure there is always a background level of nutrients, but the nitrogen and potassium ratios can be adjusted at different stages of growth.

A high phosphate feed at the beginning can encourage root growth and some of the newer chrysanthemum varieties require higher than normal levels throughout the growing period. It’s normal to have high potassium feeding at the start and after flower bud formation. In between, a balanced fertilizer is used and the strength adjusted to achieve plant height. The greater the amount of nitrogen the greater the internode length, and the taller the plant. Danish growers use zero phosphate to restrict growth. This is possible, but if not done by a very skilled grower it can lead to quality issues.

Bedding
Many growers expect composts to contain sufficient nutrients to sustain the crop from transplanting stage to sale. In a normal season this generally works, but all to frequently the weather is inappropriate at the time when the plants are ready. Growth hormones can be used, but if excessive the customer will find the plants stand still and don’t grow, leading to losses. This situation is very difficult to overcome. The use of a controlled release high potassium fertilizer like Osmocote Start can help, as not only is rooting better but growth tends to be more compact. This type of plant tends to hold its compact shape better and potentially still has nutrients to give some shelf life. Some growth control can also be achieved environmentally by adjusting temperature in the greenhouse.

Summary
Growing media is changing, with higher percentages of non-peat raw materials being used. Products such as bark will tend to use some nitrogen despite being as mature as possible. Bark and most organic materials tend to be high in potassium. This is especially true of green waste which can have relatively high conductivities. This all has to be taken into account when choosing a fertilizer regime.

For outdoor field grown crops more slow release/controlled release fertilizers will be used to ensure less losses of nutrients. Cost has restricted their use on large-scale holdings, but the environmental issues will dictate that conventional fertilizers are no longer acceptable. Europe is already using these products and seeing benefits.

The use of controlled release fertilizers is going to be essential for many crops in the future. There is considerably less fertilizer lost to the ground using controlled release products, so they are more environmentally friendly. In nitrate restricted zones they can be used when other fertilizers cause problems. Dual-coated products would be particularly suitable in these zones.

Water is a huge issue in some parts of the country. Controlled release fertilizers will always release fertilizer if there is sufficient water in the compost for the plant to grow. Watering can therefore be less frequent, compared with providing nutrients in the water, and even in adverse wet conditions when irrigation is not possible the nutrients are still being released into the compost.

Plants will always need nutrients but the way they receive them will change as technology advances.