The Hard Facts

The Hard Facts

The pros and cons of hard irrigation water


Our Agronomist, Mike Wainwright, gives an account of the issues faced by growers who use hard irrigation water:

"To people not involved in horticulture, having ‘hard water’ means that your kettle ‘furs up’ quickly, and it takes a lot of soap to make a lather. However, for those growing horticultural crops, having hard irrigation water causes a number of important issues and has both positive and negative impacts on plant cultivation.

Firstly – in horticultural terms what do we mean by hard water? Hard water is caused by salts that have slowly dissolved from rock deposits into the underground aquifers that mains or borehole water is often drawn from. Rivers can also contain hard water when they are fed from springs that come from these underground aquifers, such as the chalk streams and rivers of southern England. In all cases, the key constituent element of these salts is calcium. To get technical for a moment - this can be in the form of calcium sulphate (which is called permanent hardness), or calcium carbonate and bicarbonate (called temporary hardness). The treatments needed for temporary or permanent hardness are different, so it’s very important to know which is present in your irrigation water – this can easily be determined with a laboratory water analysis, so if you are unsure ask your Hortifeeds Sales Manager to help you with the process. Permanent hardness (as the name suggests) is more difficult to remove, and is thankfully not such a common problem in irrigation water. Temporary hardness is widely found in water sources in the South and East of England, and this is what the blog will focus on.

Calcium is a vital plant nutrient, essential for cell walls and all structural development, so irrigating with hard water (or acid treated hard water) provides a readily available source of an essential nutrient, which is clearly a major benefit. For most crops other than soft fruit, irrigating with even moderately hard water provides all the calcium plants require, when combined with calcium in the soil or growing media the crop is grown in.

So hard water adds vital calcium nutrition, but what about the negative impacts on cultivation I mentioned earlier? For longer-term crops such as nursery stock, the pH of growing media will increase gradually if hard irrigation water is applied. Phosphate and trace element availability is reduced at higher pH values, which can result in deficiency symptoms. In addition, adding excessive amounts of calcium and magnesium carbonate salts to the growing media can disrupt the uptake of essential trace elements. A bit like the ‘needle in a haystack’ effect, it becomes hard for plants to uptake trace element ions in minute quantity when there are large amounts of competing calcium and magnesium ions around the root zone.

Hard water also leads to lime scale build up in irrigation lines and drippers (just like I previously mentioned kettles). As these are fine tubes designed to provide precise delivery of fertigation solution, the effect of scale blocking lines can be very serious, leading to dead plants and costly lost production.

Carbonate from hard water is deposited on leaves and fruit, causing unsightly marks which detract from the visual appearance and saleability of crops – a key point for many ornamental plants, and fruit.

Now to the crux of the matter – what can a grower do to reduce the problems caused by hard water? For larger nurseries with very hard water the answer is often an automated acidification rig to dose the irrigation water, reducing bicarbonate and pH to more desirable levels. These rigs are expensive to set up, but provide the continuous volumes of treated water large nurseries depend upon. Nitric acid is commonly used in these rigs. It’s an extremely dangerous corrosive material at the 30 - 60% concentrations used, so rigorous health and safety protocols must be in place to manage the very real risks associated with acid handling.

Smaller nurseries, and those who shy away from the dangers of acid injection rigs, can use the less dangerous citric acid to acidify hard water. Being less corrosive, more citric acid is required to acidify the same amount of irrigation water compared to nitric acid, and it’s not suitable for use in automated rigs, however it can be a practical alternative for some nurseries. Hortifeeds sells citric acid in both a crystalline form and as a 50% liquid solution. Consult your Hortifeeds Sales Manager for more information on the use of citric acid.

For many nurseries with only moderately hard water, regular use of acidified fertilisers is enough to reduce the bicarbonate and pH of the fertigation solution sufficiently without resorting to the danger and expense of an acid dosing rig. Even where the water source is very hard, using acidified fertilisers is a practical and easy step to help reduce pH and bicarbonate levels far more than with the use of standard fertilisers. Hortifeeds offers two ranges of acidifying fertilisers, HortiMix Extra and HortipHix, the difference between the two is the way the mixes are acidified. HortiMix Extra uses urea phosphate to acidify, and is available in a wide range of formulations from high nitrogen growth feeds, through to high potassium feeds to boost flowering and support plants during autumn and winter. The HortipHix range is acidified using PeK acid, and is available in 3:1:3 balanced and high potassium formulations.Ask your Hortifeeds Sales Manager for more information on our HortiMix Extra and HortipHix ranges."