Brunnings Fruit and Citrus Food, and reading a yellow leaf

Why a citrus drops its leaves, and what the yellowing is telling you

A citrus is a heavy feeder with a shallow, wide root system, and it wears its problems on its leaves, so it'll go yellow or start dropping leaves long before anything obvious happens below ground. That's actually good news, because the leaf is a fairly readable gauge once you know what you're looking at, and most of the time the answer is a feed rather than anything dramatic.

Read the pattern before you buy anything

The useful trick with a yellow citrus leaf is to look at which leaves have gone and whether the veins are still green, because the pattern points at a different problem each time.

• Whole leaf evenly pale, and it's the older leaves down low going first. That's the classic nitrogen shortage, and it's the commonest one by a long way. A citrus food fixes it.
• Yellow between green veins, on the newest leaves at the tips. That's iron, and the iron is usually there in the soil already but the tree can't take it up because the pH has drifted too high or the ground is staying too wet. Adding more fertiliser won't touch it.
• Yellow between green veins, on the older leaves. That's magnesium, and it shows up more on a tree carrying a heavy crop, because the fruit pulls magnesium out of the leaves to build itself.
• Leaves dropping green, with no yellowing at all. That's water, either too little or too much, and a waterlogged citrus drops leaves faster than a dry one does.

So the first move on a yellow tree with green veins is a pH test rather than another bag of food. The kit only reads pH, so it won't give you a nutrient level, but pH is the thing that decides whether the tree can use what's already in the ground.

What a citrus food actually carries

Brunnings Fruit and Citrus Food is a complete fertiliser blended for citrus rather than a general garden feed, which means it leans harder on nitrogen than a flowering fertiliser does and it carries the trace elements citrus are known for running short of. Go by the rate on the bag rather than a rate you remember, because citrus rates are set by the age and the size of the tree and a young tree wants a fraction of what an established one does.

Where it goes, and this is the bit people get wrong

A citrus feeds from a mat of fine roots sitting in the top 30cm of soil, spread out at least as wide as the canopy and usually wider. Piling fertiliser in a ring against the trunk puts it where there are no feeding roots at all, and it can burn the bark while it's at it.

Spread it evenly from about a hand's width out from the trunk all the way to the dripline and a bit past. Water the tree before you feed it, not after a dry spell, because fertiliser going onto dry soil concentrates and burns. Then water it in properly so it's off the surface and down where the roots are.

Mulch on top helps a lot, since those shallow roots hate drying out, but keep the mulch 10cm clear of the trunk. Mulch piled against the trunk holds moisture against the bark and collar rot follows.

When to feed

Citrus do their growing in the warm months, so the feeding follows that. A feed as the tree wakes up and starts pushing new growth, and a second one after the main flush of growth has hardened, covers most home trees. Feeding hard into the cold when the tree isn't growing just leaches past the roots and into the groundwater.

A potted citrus is a different animal. It exhausts the pot much faster than a tree in the ground exhausts a garden bed, so it wants feeding more often and less at a time, and it'll want repotting or a top up of fresh mix every few years regardless of how well you feed it.

When it isn't a feeding problem at all

Feed a tree that's short of feed and it responds. Feed one that's sitting in a wet hole, or one that's being chewed, and nothing happens except that you're out the price of a bag. If the leaves look mottled or sticky, or there are lumpy swellings on the stems, bring a leaf or a cut piece of stem into the shop and we'll have a look at it with you. A photo on your phone works too.

Shop related products

• Brunnings Fruit & Citrus Food 2.5kg. A complete citrus feed with the trace elements in it.
• Gyganic for Fruit and Citrus Trees 4kg. The organic based alternative if you'd rather feed that way.
• Manutec Soil pH Test Kit. For the yellow-between-the-veins case, where pH is the suspect.
• Brunnings Garden Compost with Seaweed 25L. For getting cover over those shallow roots.

Did you know we also carry Fruit and Citrus Food in a 5kg bag in the shop for anyone with a row of trees rather than one by the back door. It isn't listed on the website, so give us a ring on (08) 8536 4333 to check what's on the shelf, or come and have a look through the garden centre and bring your yellow leaf with you.

Read next

• Gyganic for fruit and citrus trees, and when to use it
• Soil pH, how to test it and what to do about it
• Fruit fly in the garden, and what to do about it here

I'm still better at reading a citrus leaf than I am at remembering to feed the tree twice, which is probably why mine tells me so often.

Cheers,
Candeece

Follow our Facebook page: Strathalbyn H Hardware