Lesson 3 - Leaves, greens, roots and stems
Some of the easiest vegetables to grow are the leafy greens. They include common plants such as lettuce, spinach, cabbage, silver beet, rocket and kale, and some of the more unusual including bok choy, mizuna, radicchio and chicory. They do best under conditions of high light with good soil drainage, but have relatively high nutrient needs, particularly nitrogen. Lettuce is one of the more popular greens to grow. Loose-leaf lettuce varieties can be picked within a few weeks of germination, with regular harvesting of the outer leaves extending productivity for a few months. Head-forming lettuce such as ‘Iceberg’ takes around 10 weeks to harvest after sowing. With so many different lettuce cultivars available, they can be grown all through the year, although cultivar selection and some care is needed when growing lettuce over summer. Extended heat and long-days can cause lettuce to ‘bolt’ – producing shoots that flower and then set seed. This marks the end to the lifecycle, but it also leads to bitter almost unpalatable lettuce leaves. Shading the growing plants over summer can reduce bolting in lettuce, although many gardeners grow them over cooler months of the year to avoid this problem altogether.
Another easy to grow green is silver beet, also known as Swiss chard. Silver beet is a form of the common beet (Beta vulgaris) and related to beetroot amongst others. It’s a great easy vegetable to grow and can be very productive, especially in containers. The outer leaves can be harvested just 4-5 weeks after planting or sowing and like loose-leaf lettuce, regular harvesting of the outer leaves increases both productivity and the life of the plant. In the right conditions it’s possible to extend the life of a silver beet plant to 2-3 years, almost a perennial!
Onion, leeks, garlic, shallots, spring onions and chives are all bulb-forming plants in the same genus – Allium. Until recently they were also in their own family (Alliaceae) but are now placed in large Amaryllidaceae family. Mainly grown as annuals most are in fact perennial plants, with some, such as the herb Chives (Allium schoenoprasum) bcoming almost weedy in some gardens. As a group they need to grow in very fertile soils with regular fertilising recommended over the growing period with greater spacing needed (i.e. 15 cm) for onions and garlic to ensure the bulbs develop properly. Mainly a cool-season vegetable, the seeds are best sown directly in situ into deep, friable beds during autumn or early winter, with the bulbs or stems then harvested in spring and summer. The days to maturity vary enormously amongst the alliums. Leeks and spring onions can take between two to four months from sowing to harvest, while onions and garlic are longer, from 6 to 8 months. In the subtropics, onions can be grown during the drier months of the year, but the right cultivar must be selected as onions are extremely sensitive to day length.
Root vegetables are one of two kinds – plants that grow swollen and enlarged edible taproots, such as carrots, parsnips, radishes and beetroot; and plants that grow modified storage organs (tubers) underground, either from specialised stems (potatoes) or from modified roots (sweet potatoes). All root crops need to grow in sunny locations with friable, well-drained soil that is well-balanced in terms of nutrition but is sufficiently deep to support growth and the development of the root or tuber. Soils that are too heavy or that have too much organic matter may result in distorted roots or tubers forming.
Carrots are an easy root crop to start with. The fine seed can be sown directly in rows into prepared beds with the seedlings later thinned out to an ideal spacing between plants. The spacing is dependent on the size of the carrot being grown but is around 2.5 cm between plants for small carrots and up to 7.5 cm for larger ones. Thinning reduces competition between plants, improving root growth and development and ultimately increase the overall yield. Most carrot cultivars take from between 8-10 weeks to harvest, although smaller ‘baby carrots’ can be a little less than this.
Potatoes are another excellent vegetable for beginner food gardeners. They are generally grown from spring to autumn, although in frost-free warmer climates it’s possible to plant them in autumn and then harvest them in spring. Like many food plants there are literally hundreds of potato cultivars but fall into two main types based on their growth habit and tuber formation. Determinate potatoes grow to a set height, have a bushier habit, are fast growing and have an early harvest. They also don’t need to be ‘hilled’ (see below) as the tubers grow in single layer. Indeterminate potatoes grow larger and more vigorous plants, producing tubers in several layers along the stems. They are also longer to mature and tend to have higher yields. ‘Hilling’ increases tuber production in indeterminate potatoes and involves mounding soil or mulch around the base of the potato plants leaving only the growing tip exposed. This starts when plants are 15-20 cm in height and can be done a second time if desired. Apart from encouraging more tubers on the lower stems and increasing overall yield, hilling also reduces ‘greening’ (chlorophyll formation) of the tubers which makes them inedible.
Potatoes are planted using ‘seed potatoes’, which are not seeds but rather small potato tubers or cut pieces of larger tubers that have at least two ‘eyes’ (adventitious buds) present. The use of ‘certified seed potatoes’ is always recommended. These are tubers that have been grown under controlled and disease-free conditions and are tested for serious pathogens such as Potato Cyst Nematode before released for sale. Potatoes are heavy feeders, growing best in slightly acid soils and beds that well-drained and deeply cultivated. Each seed potato should be planted at around 10-15 cm deep and spaced at 30 cm. Most potatoes can be harvested 3-4 months after planting, depending on the cultivar and the climate. They are ready to harvest once the leaves start to yellow and the plants die back.
Potatoes are also a crop that lend themselves to container growing. Always use a deep container (>40 cm in depth) and a volume of at least 30 litres. A high -quality container growing media is also needed, one that has had fertiliser added to it. Make sure the plants are lightly mulched and regularly watered as they grow. In terms of the types of potatoes to grow in containers, determinate cultivars tend to be the easiest as they are more constrained and bushier in habit, plus they don’t require hilling.
Diggers tip
Always gently dig up potatoes, being careful not to damage them during harvest.
An easy ‘stem crop’ that every gardener should try – Rhubarb (Rheum rhabarbarum). A long-lived perennial that is best in cool, temperate climates, rhubarb needs rich soils for high yields and can grow in both full sun and part shade locations. It grows from a ‘crown’, a slow-growing basal rhizome that can be divided up and replanted over winter when the plant is dormant. The crown should be planted level with the soil and left to establish for a year or two before harvesting stems. Rhubarb is not hugely drought tolerant and needs to be well watered over summer. There are both red and green stem cultivars, some of which were bred in Australia, and some that are more productive over cooler months.
Diggers tip
Like potatoes, rhubarb is also an excellent container plant! Grow it by the backdoor or on your balcony. Once established rhubarb will produce for years to come.
Further learning
Further Learning
- Your Asian Veggie Patch by Connie Cao
- Year round greens - Gardening Australia
- How to grow onions - Gardening Australia
- The Mighty Spud - The Infinite Monkey Cage