What to grow under the lemon tree?

When we moved into this house, the large front and back yards were mostly emptyish – that typical rental mix of lawn and weeds mowed erratically and impartially. Along the fencelines there were a few large trees here and there that had root systems strong enough to tap the aquifer some 11 metres down or so, and a couple of shrubs famous for surviving deserts. That was pretty much it after several years of garden senescence-without-replacement and rental “love”. I began rebuilding the garden out from those big trees, using their shade patterns and canopy as a basis for the design. Right down at the back, halfway along the back fence, was an old lemon tree. We got tree loppers to come prune and remove the one major branch that had cracked in the drought and fallen on the fence, along with the grapevine that had added the weight to crack it. So then the question for me was, what to do in that space?

See, I’m not big on monoculture. I know that plants grow better in various kinds of company, for all kinds of reasons to do with soil and atmosphere, both through altruistic sharing and sheer competitiveness. And besides any reason of logic, there’s still part of me that if it sees an empty space, has to find a plant to fill it. (Never take me shopping at a nursery if you’re buying.) I also don’t like bare empty spaces from a pragmatic point of view, first because it can kill soil, and second because barrenness takes effort to maintain. In other words, weeding. You can put down mulch and cover, but we’d arrived at the beginning of the first real rains for the year so I didn’t want to block water penetration into the soil just yet. So planting it was. I knew I’d have ongoing work to physically set up the area across the first year, with soil reconditioning and watershaping of the tree’s rainfall collection area, but I could begin the planting process straight away. I’d be using annuals, that would volunteer new seedlings each year without my direct intervention most of the time, and that would give me part of the understorey. I could also put in plants now that would begin the soil conditioning process for me.

To begin with, around one side of the lemon tree’s dripline, I planted a double row of crimson-flowered broad beans. I love these, they’re amazing plants and so beautiful in the garden. It makes me feel forgiving about the end result of those flowers being broad beans. That got the project started and in the ground. Then I spent some time looking up plants that might grow well in the conditions under the lemon tree’s permanent canopy. Mainly that was shade, because while I wasn’t planning to water the tree regularly in summer, most of the plants I was looking at would be cool-season growers anyhow so they’d get rain. The other key interest though was the nature of their rootspace. Citrus trees have a shallow feeder root system which is most active around their dripline. That’s the space you need to feed (hence the nitrogen-fixing broad beans), and to protect from competition. It’s also the area you want to keep shaded and moist or at least water retentive. Citrus don’t mind a little dryness – like olives, they have to have free-draining soil and hate any waterlogging. But they’re holding fruit over summer, and if they dry too much you lose fruit. A lemon tree intended for home and neighbourly consumption doesn’t have to have perfect productivity, but if a few small choices here and there improve things for the tree then you’re also helping keep your tree alive. So really, what I wanted was plants that wouldn’t take up a lot of rootspace in the surface layer where the lemon tree’s roots were, but which could provide shading and cover for the sandy soil so that it didn’t become hydrophobic or hardpacked over winter during the rain season. If they were plants useful to me, that was good too.

The weeds already in place were mainly wintergrasses – wheat or barley or whatever it is that comes up where someone’s laid straw. En masse their roots will block water and nutrients from reaching the citrus root zone so they needed to be mostly removed from the system. There were a couple of tall Asteraceae here and there but only a couple, so I knew the soil wasn’t already hardpacked or over-fertilised. There was also some couch grass and some oxalis creeping in from patches outside the canopy which needed to be controlled. And there was the grape vine, which had layered itself in several spots and gone sailing up the lemon tree. I confirmed that I couldn’t just use the lemon tree to trellis the grape – while they need almost identical growing conditions so work well in the same zone, and the roots of the grape tend to be in a space less wide and far deeper than a citrus feeder root system so there wasn’t competition there, the weight of the grape would continue to break branches from the lemon tree unless it was constantly managed (not happening). So that was cut back substantially. Some time on companion planting websites suggested a few possibilities, and I ended up trialling nasturtiums, lupins and sweet pea. Unfortunately it was a little late in the cool season by then, so I got only a few sweet peas which struggled along, and no lupins at all. I had trouble sourcing nasturtiums but did get two in, which did their job of covering the ground well enough to confirm they’d be a good volunteer. And they were – they left plenty of seed for this year’s season. I also tried sunflowers along the back fence simply for pretty (and possibly for bird food), with pleasant but non-renewable results (too much effort to get them germinating and growing for them to volunteer again in that space). Towards the end of secondspring I pulled the underplants and laid pea straw under the lemon tree as a cover for the four summer months.

When autumn came this year, I reworked the soil under the tree substantially. The nasturtium seeds did their thing, along with an extra packet I planted across parts of the bed that hadn’t had the nasturtiums last year. Though, to be honest, the ones that germinated were within a metre of the dripline and they’ve spread to cover the rest. The peas didn’t really self-seed – I got one, which has long been hidden by everything else. I put buckwheat on one side of the tree for insect food and green manure, and that’s gone very well. I also attempted to sow calendula, another plant from my list of likelies. I did get some growing but it was a bit late and they’ve also been swamped by the nasturtium, so I’ll try again with those next year, and also with lupins so that there’s at least one nitrogen-fixer in the volunteer grouping. I also had quite a few plants come up from the compost, mainly tomatoes. Those flowered and set fruit across winter and we had the first ripe fruit from them this week, four months earlier than the crop I’ll be officially planting. Tomatoes are really the wrong plant for under the lemon – they preference the dripline for growing spots, they’re way too competitive for nutrients and they fill the same root space. Plus they’re a touch-and-go plant in winters here anyway, they really need the warmth of summer so this is completely the wrong garden zone for them. But it was fun to see them, and most of them didn’t survive the competition anyhow.

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