Citrus – The Soil

Citrus - the soil. A woman gardener in gloves transplants a young orange tree into the soil from a small pot to a large one. Concept of gardening and care of domestic plants

The soil is the magic ingredient to growing almost anything. And citrus are no exception.

The crucial time to get the soil right is when your citrus trees are young. Immature citrus plants are particularly demanding and it pays to ensure that their needs are met right from the start. This is because if you can get them other that first hump and they thrive, the older they get, the less fussy they become.

Indeed, apart from the a spot of pruning, treating any disease or insect infestations that may appear from time to time and possibly the occasional feed, mature citrus trees – whether they are mandarins, grapefruits or lemons – tend to be happy to simple get on with things.

The Best Soil for Citrus

The majority of citrus prefer a free-draining, loose and crumbly soil. A sandy loam that holds sufficient moisture but still drains well is ideal. Areas such as Victorian Sunrayasia, Queensland’s Mundubbera Shire and the South Australian Riverland are blessed with such soil and this is one of the main reasons why they have been developed as commercial citrus growing regions. Sadly, the chances of finding such a perfect combination of qualities in the soil in your backyard are unlikely.

Although it would be lovely to consider the qualities of the soil that a house sits on when thinking of buying or renting a property, but the reality is that few of us can afford that luxury. The home gardener has to learn to take whatever nature has given them and adapt it to whatever they wish to cultivate – be it tomatoes or limes and kumquats.

As any would-be grower of lemons and mandarins will tell you, citrus like good drainage and plenty of sun. Creating ‘sun’ if the climate doesn’t provide it might be a challenge too big, but tweaking soil to make it citrus-friendly is within most of our capabilities.

Too Alkaline, Too Acidic, or Just Right?

An alkaline clay soil can be dug with gypsum. Gypsum gives the soil better drainage, but doesn’t interfere with its pH. In contrast, it you added dolomite, the pH would become more alkaline as well as changing the structure of the earth. Your garden soil being on the acid side is not a problem as most fruits and vegetables prefer it. However, dolomite on ground with a 8 plus pH makes it too alkaline and your citrus fruits may form with nutrient deficiencies. And this is not what you want to happen.

Introducing gypsum and dolomite to close, dense soils is important to open up their structure. This allows for better drainage which in turn prevents root rot. It is Nature’s ultimate joke that plants need water to supply them with nutrients and yet so many of them loathe being too wet. And citrus are especially touchy about getting water-logged. This means that decent drainage is essential.

Having said that, citrus trees aren’t fans of excessively sandy ground either. This is because the nutrients move past their roots too quickly for them to get their full benefit. Trying to keep a very sandy mix moist enough for your lemons to get sufficient nutrients can become a full-time job and is ultimately not worth the effort.

A general rule of thumb is to include some loam in a premium potting mix when if you are trying to get citrus to thrive in tubs, pots or containers. Most premium potting mix that you buy for hanging baskets etc is free draining as its been made largely from rotted pine bark with a bit of copra or peat moss added to hold water. Sadly, a perfect potting mix that drains well and yet retains the ideal balance of water would either be too heavy for shop shelves or too expensive to actually blend in the first place.

Try adding 20-30% loam and a handful of Zeolite to generic potting mix blends for tub-raised citrus. The combination of the loam and Zeolite really assists the exchange of essential nutrients such as calcium, potassium and magnesium for the plants. This is because the pieces of loan provide more surface area for the nutrients to attach to on their way through the planting medium. The result is that the fertiliser you’ve spent good money on goes to your tangelo plant and doesn’t seep straight out of the bottom of the tub.

Soil pH and Mineral Deficiencies

If you are serious about growing citrus, it might be worth investing in a pH testing kit to keep track of soil alkalinity or acidity. Otherwise, you can adopt the traditional approach of simply scooping up a handful of earth and smelling it. A sweet scent means it is mainly alkaline whilst sour indicates acidic. And if it isn’t really sweet or sour, then the chances are it is neutral.

Soil pH is particularly important when nurturing citrus as most of their essential nutrients are only taken up by the plants during their growing periods, when the ground is moist and within their preferred range of alkalinity and acidity. If the soil is too alkaline, citrus will only take in iron compounds erratically and will actually absorb very little once a pH of 8.5 is reached. At this point, your citrus are in danger of developing iron deficiency or lime-induced-chlorosis (LIC). Adding mineral iron rarely reverses this problem as plants cannot soak up ferrous iron.

If you’d like to know more about the importance of soil pH, see here.

A pair of hands holding rich, dark soil

Also, although red clay alkaline soils are often rich in iron, the very alkalinity of the earth ties up the iron, making it inaccessible to your plants. When this happens, try adding iron chelates to your mix. You’ll know if they are having the desired effect if the plants yellowing leaves return to a vibrant green.

Of course, things are rarely that easy and often signs of LIC indicate other nutrients deficiencies aside from a lack of iron. For this reason, it is generally a good idea to include a complete mineral complex or a specialised citrus fertiliser at the same time as you introduce the iron chelates. It’s might be a scatter-shot approach, but it is a practical one as you are hardly like to take and analyse soil samples from all over your home garden to assess what each individual flower, vegetable and fruit tree requires. For the backyard gardener, covering as many bases as possible with a range of nutrients is your best bet, even if it means that sometimes your are applying an excess of nutrients.

Remember that a good compost will cure a variety of ills in the garden. It not only provides nutrients, but is also the sponge through which the vital nutrients exchanges take place. Unless you are dealing with plants which can tolerate hydroponic or even aquaponic growing systems, even chemical fertilisers are more effective when they are released into organic material for a rapid nutrient uptake. For more on Feeding Citrus, see here.

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