Of all the fruit trees, Citrus are the most popular backyard trees in Melbourne. Citrus trees are attractive evergreens and fit well into the garden landscape with their glossy green foliage, beautiful white scented blossoms and colourful fruit. Here’s our guide on where in the garden you should plant your citrus trees with plenty of advice to ensure you give your new trees the best start possible!
Site selection for Citrus Trees
Citrus plants grow best in an open position where they receive at least 5 hours of full sun each day, during the growing season (October to April). The more open and sunny the position is, the more accumulation of sugars in the fruit. To maximise heat units and frost protection, plant your trees in a north facing position, preferably in front of a brick wall. The brick wall will reflect heat and light onto the tree during the day and radiate absorbed heat back onto the tree during the night time.
Most citrus grow and fruit best, in a temperature range between 20 and 32oC. Both above and below this range, growth slows and stops completely below 13 degrees C and above 38 degrees C.
Shelter is important, because strong winds damage young growth, blossom and developing fruit.
Freedom from frost is desirable, although most citrus will tolerate light frost, once they are well established. Late winter and early spring frosts can damage young blossom bearing shoots. Trifoliata rootstocks induce a shorter growing season, and help reduce the risk of damage.
Citrus growth and fruiting can be limited by the tree’s tolerance to winter cold and by the amount of heat, required in a season to mature the fruit. In colder areas such as the hills, grapefruit, ‘Valencia’ orange and sometimes ‘Washington’ navel orange may not mature fully and may develop “off-flavours”. In areas prone to severe frosts, limes will not survive and the thin skins of some mandarins may be damaged.
In difficult climates, it may be better to grow trees in tubs in the sunniest and most weather protected site available. A north-facing brick wall will radiate heat at night to keep temperatures more constant. In winter, trees can be moved to a more protected area, away from frosts.
If planting trees in a lawn try to exclude the lawn for 2 metres from the trunk to reduce competition for nutrients and water.
Citrus grow best in well drained and aerated, sandy loams with a topsoil 50cm deep or more. Citrus root systems have only moderate vigour, and are concentrated in the top 30-50cm of soil. The site should be free of roots from other trees, as citrus roots compete poorly with roots from other trees.
Good drainage and aeration are crucial to preventing “root-rot” in citrus. Low lying sites that retain rain-water should be avoided.
Trees often fail to establish in clay soils unless good aeration, drainage or mounding is provided.
pH range is preferred to be 6 to 8.
Preparing the site
Ideally, prepare your site in autumn for planting in spring.
Dig over an area of soil, a metre across and 30 to 50cm deep. Incorporate plenty of compost, organic matter and well-rotted manure. For planting in clay soils, incorporate up to one kilogram of gypsum to the soil. If soil is particularly acid (below pH5.5) use a small amount of lime. Back fill the hole to allow organic matter to further decompose over winter.
Problems with shallow or heavy clay soils can be overcome.
If available, deep ripping will improve drainage and long term root penetration. Use 2kg per sq metre of gypsum and a 15cm layer of clean sand over the site. Deep ripping should be to at least a depth of 40cm or more.
Alternatively, sandy loam can be mounded up to provide better drainage and soil depth. Be aware that the negative ionic charge of clays, will draw moisture from the loamy soil on top and dry it out. So ensure that the two are mixed reasonably well, to prevent the root systems drying out in winter.
Buying your Citrus Trees
Citrus trees are available to purchase all year round as container, propagated specimens, in potting mix. However, fresh trees come into many nurseries during autumn. Buy healthy trees, with fresh mature green leaves at this time. Do not transplant the trees in winter. Instead hold them over in the pot, in a sheltered, sunny spot for planting in spring.
Select trees that have no evidence of damage to the stem, other than the natural kink at the bud union with the rootstock.
Remove any fruit. The presence of fruit is not an advantage except to confirm that you are purchasing the correct cultivar. In fact, the presence of fruit may indicate a tree left over from last year. Healthy young trees are preferred to these older specimens.
The best time to plant citrus trees is in spring from September onwards. Soil temperature is ideally at least 16oC. Do not plant young trees in cold soil.
Washing off the potting mix
Although it may seem radical and contrary to conventional advice this is the recommended method for planting
Fill a large bucket with water and place the tree, pot and all into it to soak for 10 minutes. Slip off the pot, taking care not to damage the roots.
Gently pump the tree up and down in the water to loosen and remove the potting mix. Using your fingers, free up and extend the roots.
Continue this until all of the potting mix has been removed and it is bare rooted. Keep the tree in the water, while preparing the planting hole, but for no longer than a couple of hours.
This process allows the new roots to grow directly into the soil, thereby avoiding a sudden change in planting medium from potting mix to soil.
Re-dig the hole
Return to your pre-prepared site and re-dig a hole twice the width and depth of the tree container. Add further compost to the bottom of the hole. Replace enough soil, so that the tree will be replanted to the same depth, that it was in the container.
Placing the tree
Centre the tree in the hole and gently hand fill close to the roots. At the same time spread the loose roots out and down as widely as possible. Gently back-fill the soil and lightly firm down.
It is important to avoid planting too deeply because citrus are surface feeders. Later attempts to correct incorrect planting, are not usually successful.
Citrus care after transplanting
Form a rim of soil 10 cm high around the tree, just outside the size of the original hole. Fill this with water from the bucket that has the surplus potting mix in it. On the following day re-firm the soil and top-up if it has sunk or cracked and a little more water.
Usually, the tree only needs watering every week, unless the tree is showing signs of wilting. To check for wilting, observe the condition of new growth, this is a great way to judge when to water next. If the mature leaves feel warm and leathery (as opposed to cool and transpiring) then it may also need watering.
As a guide, watering of newly planted trees can be as little as nil (after rain) to twenty litres weekly in cool weather and up to 20 litres every second day in summer.
Cover an area of at least a metre in diameter around the tree with an organic mulch up to 10 cm deep. This will prevent weed growth, conserve moisture, moderate soil surface temperature and help to spread and retain water.
Avoid using woody mulch which may cause nitrogen drawn down in the soil. Straw is the best mulch for citrus trees.
Mulching trees in pots or tubs is just as important.
Sun and Wind Protection
Provide a windbreak shelter out of shade cloth or hessian in windy sites and consider staking the tree until it has established.
In hot summer weather sap flow can be affected, particular when very hot days, rapidly follow a cool period. To avoid heat and UV damage to the bark, consider painting the trunk white, with some water-based interior house paint.
Young-rapidly growing trees, need a constant supply of nitrogen. Small regular applications give the best results.
Sprinkle a nitrogen rich fertiliser onto the moist soil and rake into the surface lightly. You can use a pre-formulated citrus fertiliser or chicken manure will work just as well.
Want to know more about Growing Citrus in Melbourne?
This is Part 2 of a 5 part guide to growing citrus in Melbourne. The links below will take you to the other four parts of our Melbourne citrus growing guide.
Our citrus growing guides are based on my own experience, as well as the following two books. They are both invaluable resources for the home gardener based in Melbourne. I strongly recommend you have a read of both if you want to know more about growing citrus in Melbourne:
Bruce Mophett & Ian Tolley: Citrus, A Gardener’s Guide, 2009.
Louis Glowinski: The Complete Book of Fruit Growing in Australia, 1997.