One of the things that is generally not considered when thinking about plants and trees is how easy they are to deceive. Most people would acknowledge that the average plant needs water and sunlight above all else to survive and grow. This is certainly true but even plants can have too much of a good thing. In the laboratory, plants that are normally dormant in winter can be persuaded to grow non-stop, in some cases for up to 3 years, by ensuring that they have plenty of light, water, food and warmth. The problem is at the end of this they are so exhausted that they die even though their normal life expectancy is several hundred years. Less dramatically, chrysanthemums are persuaded to flower at unseasonable times of the year by reducing light levels.
Plants need rest
All long-lived plants, shrubs and trees need regular periods of rest. Pretty much like every other living organism, including humans. In northern climes, this rest is achieved in winter. It is triggered by a combination of a reduction in daylight hours and falling temperatures. These 2 factors combined alert plants to the onset of winter when growth is difficult or impossible. Their intelligent response is to go to sleep until an extended period of rising temperature wakes them up so that they can enjoy the longer warmer days ahead when growth is easy.
We have all seen this process occurring in both reactions in the last 2 years. The spring of 2013 was extremely cold and tremendous damage was done to plants across the UK, for example in orchards where blossom on most fruit trees came early and was then killed by frost. It came early because February was unseasonably warm and tricked plants into coming out of dormancy. In 2014 by contrast there was almost no cold weather between November and April. As a result some plants never went into dormancy, and there was wide reporting of "interesting" occurrences such as fruit trees and roses in flower in February.
What is the cold store?
At Ashridge Nurseries, we have sought to trick our plants in a beneficial way. We have two large, purpose built on cold stores with a total area of 750 square metres (7500 square feet). They have insulated walls and roofs almost 100 mm thick. There is even thermal insulation under the concrete floor. We run our stores at +1°C and over 97% humidity which is monitored 24 hours a day. Anyone who has hair that goes frizzy in a damp atmosphere would hate them. They are cold, damp and dark. Absolutely perfect for dormant plants which, if they could talk, would probably equate our store with your bed.
These conditions are maintained from the end of October to the middle of May. They mean that all our bareroot stock gets a full winter's sleep between the time it is lifted and delivery to you. The last delivery into the store is weather dependent but generally around the end of January to the middle of February to ensure that the plants going into storage are still fully dormant. That way, nothing wakes up too early and there is no stress on the plants caused by unseasonably warm or cold weather. The only exceptions to this regime are a number of evergreen plants which do not go into full dormancy ever and which prefer high light levels to allow them to retain their foliage.
When your plants are taken out of the cold store and delivered to you, they respond almost instantly to the change in light levels and temperature. In April and in May, not only are the days longer and warmer, the soil is warmer as well. The effect of planting young trees, shrubs and hedging into warm soil can be quite dramatic. In 2013 we delivered pear and apple trees to a customer who is a professional grower in mid-May. He had also had a delivery from us in January. The plants delivered in May, which were completely dormant, were in flower in mid-June and by the time they dropped their leaves in late October, they were better developed than the ones which had been planted nearly 4 months earlier.
As with all our stock, plants you buy that come from the cold store are guaranteed in terms of quality and establishment. And just like you, they do better after a good, uninterrupted sleep. The only difference being is that their sleep lasts all winter.