Shopping Cart

No products in the cart.

Brains Trust

Answered by Angelo Eliades of

I grew a green manure crop to add nitrogen to the soil (using broad beans), but last time I did this, I planted summer tomatoes straight after digging the broad beans in and it was the worst tomato crop I’ve ever had. What went wrong? (Emma, Newcastle, NSW)

Growing plants in unfinished compost doesn’t work very well. When we dig plant material into the ground, the soil bacteria will use some of the available soil nitrogen to break it down into compost, taking it away from the plants. This phenomenon is known as nitrogen drawdown. If there was insufficient nitrogen in the soil to begin with, there would definitely not have been enough left after composting to support the growth of heavy feeders such as tomatoes.

When using broad beans as a green manure crop, use the chop-and-drop method: cut the stems at soil level, so the roots decompose and release the nitrogen into the soil. The green leafy growth (despite its 30:1 carbon-to-nitrogen ratio) should not be dug into the soil; it should be chopped and left on the soil surface. Even better, the chopped plant material on the soil surface can be lightly sprinkled with manure, then covered with a straw-like mulch to create a no-dig gardening, sheet composting system.

Permaculture seems to lean towards perennials as much as possible to reduce workload, however I love our annual vegetables. I have some perennials for leafy greens, but are there really any good perennial substitutes for broccoli, cabbage, tomatoes, cucumber and green beans? I’m in cold/ temperate climate. (Jean, Somerville, VIC)

Perennials are preferred in permaculture because they typically have deeper roots and use much less water, and usually need much less fertiliser because they’re long-lived slow feeders.

Tomatoes are in fact subtropical perennials but don’t survive the cold. Tamarillos can tolerate cold, and are used as tomato substitutes for some recipes, but not many. Tomatoes could also be grafted to a devil plant and grown in a greenhouse to create a perennial tomato tree. Nine-star perennial broccoli is available, but does terribly in cooler climates, from my experience, unless it’s in a very protected spot or a greenhouse. Salad burnet is a perennial herb whose leaves taste like cucumber and can be added to salads if it’s just the flavour that’s required. Perennial seven-year scarlet runner beans grow well and can be used dry or fresh, but aren’t the same as common green beans – they’re a different bean altogether.

From a permaculture-thinking perspective, we’re quite spoilt for choice with both vegetables and cuisine available from all around the world; never in human history have we been so privileged. If we want the rewards, we do need to make the effort. If time is limited, grow the annuals which are most important.

Is it really necessary to rotate garden beds for all vegetables? I don’t know if I’ll ever be that organised. And sometimes self-seeded vegetables come up where they were planted. (Chris, Marden, SA)

Yes, annual vegetables must be rotated, otherwise localised nutrient depletion will occur, which can lead to nutrient deficiencies, as some vegetables will take up more of certain nutrients and less of others. Furthermore, if the same vegetables are grown in the same spot year after year, pests and diseases favouring those plants will gather there, and eventually destroy the crop. Once tomatoes get root node nematode, growing any plants from the Solanaceae family in that location will no longer be possible!

Many vegetables do self-seed well, and seedlings can be relocated by carefully digging them up, keeping root disturbance to a minimum, and replanting them in a better spot in the garden.

There are various crop rotation systems, and some are easier than others to manage. Admittedly, rotating by plant families can get a bit complicated. I’d recommend using the three-group rotation system of heavy-feeders, heavy-givers and light-feeders: it’s very easy to manage. Refer to the article I’ve written on page 26 (A Bountiful Garden All Year Round).

Should I cover my garden paths with creeping plants? I’ve already tried wood chips, newspaper, covering the weeds with black plastic, and just letting the weeds grow there (without too much success). My main weeds are kikuyu, clover, stinging nettle and others. (Sue, Moruya, NSW)

Plants aren’t grown on paths because they don’t grow well in compacted soil and dislike being walked on. The only exception to the rule is where pavers or stepping stones are used, with the spaces between them filled with low-growing lawn-substitute plants.

By the way, nettles are extremely useful plants: they’re a great compost starter, a super-nutritious cooked green and an excellent companion plant in the garden!

The best method to get rid of lawns or weedy paths (which has been used with great success in countless school gardens), is quick and easy to implement. Step one (this is optional), sprinkle some fertiliser over the area to help plants break down quickly after they die. Step two, cover the area with whole opened newspapers or flattened cardboard boxes, overlapping by one-quarter over each edge. So that they lay down better, boxes need to be pre-soaked; newspapers can be watered lightly after laying them down. Step three, cover with a layer of coarse woody mulch seven to 10 cm thick. Step four, eliminate any new offending weeds by pulling up any new growth that pokes through, or by pouring boiling water over them.

Water is getting really scarce where we are. Is there a best way to water my garden to make the most of every drop I can spare (i.e., time of day, overhead, drip or sprinkler)? (Julia, Barcaldine, QLD)

Dripline irrigation, which drastically reduces water loss due to evaporation and runoff, was first developed by a company in Israel to deal with their harsh arid conditions, and has become popular worldwide in locations where water is scarce: it’s the way to go. The most effective way to water a garden and spare every drop is to use dripline irrigation located underneath a layer of mulch.

Water in the late evening to minimise evaporation caused by intense summer heat and hot winds. Set tap timers to a watering duration of one hour so the plants receive a long, deep watering. This encourages their roots to grow deeper into the soil, which enables them to access more water, making them more drought-tolerant.

With dripline, the emitters that drip water are spaced 30 cm apart and release two litres of water per hour. Locate new plants next to emitters on the dripline so they receive adequate water when first planted.

I read somewhere that we can be planting our vegetables much more closely together than the traditional spacings on seed packets. At what point will they start to steal nutrients off each other? (Gabby, Springfield, TAS)

The origins of this idea have an interesting history. In England, where a lot of our gardening practices originate, they have plenty of water but very little sunlight, so plants are spaced further apart to receive adequate light, whereas here in Australia, we have quite the opposite: plenty of sunlight but little water.

The distance between plants stated on seed packets or seedling labels is often the hard physical limit determined by the size of the actual plant. When planted at these distances, the plants will touch their neighbours, and there will be sufficient soil nutrients for good healthy growth.

Where the planting distances can be changed is the distance between rows, which can be much narrower in sunny Australia. Planting using a ‘square foot gardening’ system, where plants are planted in blocks, eliminates rows altogether.

In permaculture design, by using staggered rows of plants grown close together, more efficient use can be made of available space, minimising empty space while maintaining the space required for each plant. Much like filling a kitchen drawer with jars, if all rows begin right up against the front of the drawer and line up in neat rows, only the outermost edges touch, creating large diamond-shaped spaces between them, but if the rows are staggered, the jars lie much closer together, forming a honeycomb pattern, so more jars can fit in the same space.


Leave a Reply