Plant Citrus: Dealing with Frost and Clay

Fruit Tree No 29

Having bought this property 18 months ago, I’ve spent a good 12 months observing, thinking and planning my edible garden. From autumn-spring this year I’m planting a lot of fruit trees. Today I planted no 29: my first citrus tree. It’s called a Thornless Lemon, and is apparently a thornless Lisbon.

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Before now I’ve only had citrus in pots, and not been greatly successful either, in rearing thriving specimens. I say before now because I notice really good growth and flowers on my potted citrus this spring. The secret? Feeding and watering! But I digress. As a theoretical open-ground lemon grower, I find the topic perplexing. Citrus are supposed to be the great Australian backyard fruit tree, easy to grow with bountiful crops. Yet every second question on every gardening show or forum, seems to be about problems with citrus. In my town I have the added bonus of regular frosts through autumn-spring, and clay soil to add to the challenge. But I know citrus can do well in these conditions because there are loads of healthy looking mature trees around my neighbourhood.

So, after reading up and asking around, I decided on a course of action to prepare my citrus to cope with my climate and soil. Here are the steps I took:

1. Decide When to Plant

While you can plant evergreen trees in autumn, in a cool climate with regular frosts, leaves, particularly young, sappy growth, can be burnt and killed off by frost. I believe frost can also damage trunks but don’t know about this – I need to read up.  Frost is a problem for young trees because they have fewer leaves and so fewer leaves to rely on if they lose outer leaves to frost. This leaves the tree vulnerable to not having enough leaves to photosynthesize. So to give the tree the best chance of growing and sending out roots before frosts hit, I am planting in spring.

2. Choose Location

Citrus are subtropical plants, so as a general rule thrive in mild climates, with full sun all year-round. For my lemon, I chose this spot behind the rosemary bushes in the front garden:

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This spot is on a hill, and should provide some protection from frost, which tends to flow down-hill:

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Looking down from next to spot for lemon.

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Looking up the hill.

 

 

 

 

 

 

 

It also has some existing protection from established evergreen trees uphill from the lemon (the row of trees in background, leading back from the letterbox) – hopefully this will help both by preventing some heat from escaping and by directing the cool air around the lemon and down the hill:

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It is also to the south of a deciduous tree (a Golden Ash I’m told), letting sun through in winter to help the lemon get year-round sun.

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3. Prepare the (Clay) Soil

Citrus thrive in nutrient rich, well drained soil, and they don’t like to dry out. We have clay soil in our area, and  although clay soil is often rich in nutrients, it gets waterlogged easily, particularly over winter. In winter it can get really hard and if left to bake, can make it difficult for water to penetrate the surface. This leaves the trees root ball vulnerable to rotting or drying out. So I’m improving drainage by digging in lots of compost, sand, and straw, to form a raised mound (see point 4 below) and improving the nutrients in this mound of organic material by adding pelletised chicken manure and mulching with lucerne. I use coarse builders sand that my landscape gardening supply place sells by the bag for $6.95 (back warning: extremely heavy for a smallish bag!). I read somewhere to use the coarse sand as the fine sand may actually impede drainage and contribute to water-logging.

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4. Raise Mounds

I am planting my lemon in a mound with the rootball essentially sitting on the surface of the existing clay soil, as recommended by the Urban Food Gardener here. Hopefully you can see the mound in the picture below. The mound is about 20cm above ground level.

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5. Install Frost Protection Frame

I will be protecting my lemon tree from frost for the first few years at least by setting up a frame over which I can attach shade cloth or frost protection cloth (not its official name). I drove in 4 x 135cm star pickets, driven about 40cm into the ground, at this point so as to avoid doing any damage after the tree was planted, either to its roots or foliage. At some point I will attach polypipe of some description to these pickets, forming a dome, and then peg or tie the shade cloth to those.

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6. Plant Tree

Hopefully you can see in the shot below how much above the ground the tree is sitting. Basically the bottom of the potting mix/root ball is sitting level to the ground, and the top of the potting mix is level just above the top of the mound.

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7. Stake Tree

When you plant your tree above ground level, it will be very vulnerable to blowing over in strong winds, as its roots – which you can see in the shot below are teeny tiny – are not strong or entrenched enough to hold the tree in the soil. Do the staking at this point, before you fill in the soil around the root ball, so you can see where the tree’s roots end and avoid damaging them with the stake. I used a wooden tomato stake of about 120cm in height and thumped it in with a mallet as far as it would go – not far in hard clay. I used horticultural tie,  available from any hardware store, to tie the tree to the stake in three spots, with a bit of give at each so the tree has some free movement. The tie feels like a thick opaque stocking material.

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8. Create Basin/Crater

Because I have created a mound, if it was a pyramid shaped mound, the water would just run straight off. So be sure to create a crater effect around the tree. This will help direct the water to the trees roots – towards the drip line (where the outer edge of the circumference of the tree’s canopy/foliage ends and water drips down onto the soil below). This is supposed to help the tree’s roots spread out further looking for water, creating a more resilient tree.  I am also going to set up a drip irrigation line around the tree’s drip line like the one that Tino Carnevale from Gardening Australia does at the end of this video.

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9. Water In

I used diluted seasol. Seaweed solution is not a fertiliser really, but among other things, helps plants take up nutrients more effectively and helps reduce transplant shock. I didn’t really fiddle with the roots too much or remove too much of the potting mix like I have been advised to do (mostly because they seemed very fragile) so I’m not sure how much shock the tree will suffer. But I thought I take the precaution anyway:

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10. Prune – Optional

You don’t really need to prune citrus trees much, or so I read. I decided to prune this one back just a bit as there is some growth (I realise it’s a little hard to see in the shot below) that seems overly tall and gangly and weak.

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I thought it might help to make a stronger structure by snipping it back, as well as encourage bushing out (which will make picking lemons easier down the track):

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11. Mulch

I used lucerne, which is high in nitrogen and breaks down easily. To repeat, citrus are hungry feeders and require lots of nitrogen. Lucerne is not cheap – about $18 for the packet pictured below. Like other packaged mulches, it comes with a guide of what area it will cover when spread at a certain thickness. I put a thin layer because:  (a) if you layer fine mulch too thickly it will prevent water from getting through and (b) it’s only mid-spring, which in a cool climate means we could still get quite a bit of cold weather, and I don’t want to prevent the soil from warming up.

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12. Pick Flowers/Fruit?

My tree has about 12 flower buds at the tips of branches – which is where a lemon fruits. Some people will tell you to pick these off because the tree puts too much energy into fruiting when, as a young tree, it should be using its energy to growing foliage and sending out roots. I think this advice is one of those things you hear a lot but whether you need to do it really depends on so many variables. In my case, I’m not in a particular hurry for the tree to grow, and I would be surprised if the tree held onto any fruit that set anyway, leading into warm weather and having just been planted out. So I’m leaving them on. If I get a lemon, I will cherish it.

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2 thoughts on “Plant Citrus: Dealing with Frost and Clay

  1. Sounds like you’ve given it a really good start in life. I can’t see how it could fail to thrive. The tree knows what’s best for it. If it wants to hold onto the fruit it will. Enjoy your lemon/s.

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  2. Pingback: Plant Citrus: Dealing with Frost and Clay | bluetongue greenthumb | WORLD ORGANIC NEWS

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