The Use of Seaweed/Kelp for Frost Protection.
Seaweed Digests for Critical Spring Temperatures for Frost or Freeze Damage
Given the weather patterns we have experienced so far this late winter and early spring, a spring frost seems very possible. Once the fruit has set, then the critical temperatures that can damage the fruit become lower. We will need to constantly assess the stage of development our trees are at over the next weeks and their susceptibility to possible freeze injury.
If we continue in a spell of colder weather, apple trees will continue to develop more slowly, but once they begin showing tight cluster, pink and bloom, the critical temperature rises from the low 20’s to the high 20s, to levels just below freezing at bloom time, which is the most critical time to get frost damage.
Our experience here at Royal Oak Farm Orchard and from scienti fic studies both in Australia and other overseas locations have shown that regular application of seaweed (kelp) digests can increase frost resistance. Low concentration seaweed digest applications at about 10-12 day periods through out the frost danger period can give 2 to 3 degrees of extra frost tolerance for apples and stone fruit. A suitably chosen seaweed extract can be the grower’s best defense against late frost at blossom time.
When choosing a seaweed digest several factors need to be considered:
• Seaweed digests are often tailored for use on a particular crop and are fortified with conventional fertilizers or organic sources of nitrogen. Those that have added nitrogen may well reduce rather than increase frost resistance because of the effect of the nitrogen producing sappy growth. They should be avoided when the aim is to increase frost tolerance. Foliar sprays of Fish /Kelp mixtures should be avoided for this reason. It's best to stick with a 0-0-1 Seaweed mix like Neptune's Harvest Seaweed Plant Food..
• Most of the scientific work showing increase frost tolerance by seaweed digest application has been based on alkaline digests but acidic digests also appear to work. It is not clear that fermentation produced extracts work as well. Further, it might be expected fermentation - produced extracts may be counter productive, as the spores present may well be ice nucleators.
• Digests that have a relatively high potassium level may be superior to those with low levels because of the effect of increase potassium uptake by the plant through the foliage.
• For foliar application of a seaweed digest, it needs to be applied as a fine spray. It should have been passed through a ne lter during the manufacturing process.
• The digestion process needs to be carried out carefully as it is desirable that the product once on the buds or foliage is slightly sticky and forms a very thin layer over the leaves.
Seaweed digests increase frost tolerance in several ways.
• They contain a number of plant growth regulators, two of them, (cytokinins and betaines) increasing turgidity of the cell wall.
• They contain sugars, such as mannitol, and also potassium both of which will lower the freezing point of the cell fluid and explain part of the observed effect.
• Extensive work by scientists in the UK seems to indicate that there is something in the digests that triggers a gene responsible for “hardening off” the plants.
Whatever the mechanisms involved numerous studies have shown that liquid seaweeds can reduce frost damage in a wide range of crops. Liquid seaweeds forti fied with potash and/or other minerals are more effective than pure liquid seaweed.
Frost damage can be signi cantly reduced in apple crops by developing a strategy. Liquid seaweed application every 8 to 12 days during the frost danger period should be an important part of that strategy. This would be expected to give an extra 2 to 3 degrees of extra frost tolerance. The first application should be made at least 36 hours before the expected frost. The total number of applications will depend on the location but typically up to two to six applications may be warranted, depending on predicted temperatures.
Scientific Studies Cited:
https://link.springer.com/article/10.1007/s10811-015-0574-9
https://www.frontiersin.org/articles/10.3389/fpls.2019.00655/full
Home Orchard Management @ Royal Oak Farm Orchard
Home Orchard Management @ Royal Oak Farm Orchard is a blog for the home fruit tree grower providing information about fruit tree management, fruit tree pruning & training and Integrated Pest Management from the IPM Specialist and Certified Nurseryman at Royal Oak Farm Orchard, a 20,000 tree apple orchard and agri-tourism operation located in Harvard, Illinois.
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