Seeds and Sowing Times

Failure in the beginner's vegetable garden is often due to attempting to grow crops at the wrong time. Sowing tables that are averages for your district are a guide only. Some years the growing season is cool and late, other years it is warm and early. While it is possible to grow extra early, or late crops, this is more difficult than growing at the ideal time. The especially early, or slow bolting varieties have been bred for that characteristic alone and often lack the full flavour of less tolerant varieties. Altering the growing environment to extend the season with cloches and greenhouses is covered in Extending the Growing Season.

Carrots and beetroot, for instance, sown into ground that is too cool will germinate, but will be prone to viral disease and never give of their best. Seeds sown three or four weeks later will rapidly overtake those sown earlier. Again using carrots and beetroot as an example, there must also be sufficient time for them to reach maturity before the onset of cooler weather.

The following tables give the optimum growing temperature ranges and soil temperature conditions for vegetable seed germination. Most seasons, using a thermometer and this table will be a much more accurate guide to sowing times than the following tables for cool, temperate or tropical conditions.

Planting Distances

One thing plants remain blissfully unaware of is our concept of distances. Seeds scattered in the wild fall on the surface of the soil, not 10 mm below. The germination rate is considerably lower than we can tolerate, however. In general, sow seeds shallower in cool, wet conditions and deeper in hot, dry conditions.

Spacing between rows is determined to allow free passage of the gardener through most, if not all of the growing season. If you are growing in raised beds with semi-permanent footpaths between, as many do these days, ignore the between row spacing.

Spacing between plants can be closer if the soil is above average in fertility, further apart if the reverse obtains. In general, closer spacing results in smaller plants, but higher yields. In a very humid climate, close spacing can be an invitation to fungal disease. Different varieties require adjustment and only your preference and experience over a number of years will enable you to optimise these distances.

Seed Raising Mix

When sowing seeds in punnets, pots or flats, ordinary garden soil will not do. The best seed raising medium is generally made up of three equal parts of sharp sand, good garden soil and peat moss. Turfloam can substitute for garden soil. Make this by stacking cut grass turf in heaps and cover. Leave for twelve months. Compost can be substituted for peat moss. A tight handful of dolomite, blood'n'bone and seaweed meal are beneficial. The mixture should be both water retentive and free-draining. During the growing period, water from below by preference, in order to avoid soil compaction and washing. Light seeds can easily float to the surface. Covering the containers with a sheet of plastic or cardboard until the seeds germinate is a good practise, as it prevents the soil from drying out. The cover must be removed immediately the seeds germinate, though. While the seedlings are growing, they must receive adequate light, or they will be weak and spindly.

Damping-off, a fungal disease that particularly afflicts brassicas, by attacking the stem at soil level, making the plants keel over, can be a problem. Covering the seeds in the punnet with sand rather than seed raising mix can help here, as can watering with dilute chamomile tea. Sphagnum moss also has mild fungicidal properties.

Transplanting

When transplanting most seedlings, plant them a little below the level they were at in the punnet. Tomatoes benefit from being planted very deep. The roots are then well into the zone of moisture, and further adventitious roots will arise from the stem.

Crops that do not mind being transplanted include: asparagus, cabbage, capsicum, cauliflower, celery, silver beet, egg plant, leek, lettuce, onion, tomato. The rest are all best sown where they are to grow to maturity. If the truth be known, it is best to sow all crops direct. There are several reasons for transplanting, however.

The first reason for transplanting is that where the growing season is short, crops like tomatoes, egg plants and capsicums are best sown indoors, long before the weather is warm enough to plant them outside. If you waited until the weather was warm enough to sow the seeds outside, the crop would not have a sufficient time to mature. The second reason for transplanting is that it gives you a longer period to reduce the weed-seed population in the growing bed, using the rake. Alternatively, you can be growing a crop and transplant into the bed immediately it has finished. Seedlings do not require the large amounts of space that the mature plants do. This is an advantage when controlling cabbage moth caterpillars in your brassicas. Less of the expensive 'Dipel' spray or hand picking is needed.

When transferring plants sown indoors to their final outside positions, a period of acclimatisation is necessary. This is referred to as hardening off. If these plants came from a nursery, it is good practise to harden them off as well, since they are generally very pampered before coming to you. Failure to observe this procedure will at worst kill the plants and at best, they will 'sulk' and never give of their best. Hardening off consists of exposing the plants to longer and longer periods outdoors for a period of a fortnight, until they can be safely left out overnight.

When transplanting seedlings into their final position, firm the soil around their roots to eliminate any air pockets and water them in with a dilute seaweed tea. The watering in greatly increases the 'take'. If the weather is windy and/or warm, remove some of the leaves on top, to reduce the amount of water loss by the plants. This is particularly necessary where significant root disturbance (damage) has taken place. In extreme conditions a shading device for the first few days will help reduce losses.

Moon Planting

Many gardeners sow their seeds and transplant according to the phases of the moon. Given the dramatic influence the moon has on terrestrial conditions, the tides and so forth, this seems a perfectly reasonable thing to do. The slightly shorter than a month period between full moons is an almost ideal interval between the sowing of successional crops, such as lettuce and peas. Unfortunately, there is not just one system of moon planting. The biodynamic growers sow seeds just before the full moon and transplant just before the new moon. Biointensive gardeners sow their seeds just before the new moon and transplant at the full moon. Since both schools of thought, and doubtless there are others too, all get good results, I believe that the weather has the greater influence on the outcome of gardening activity.

Maintaining Records

What does make more sense is to observe the seasonal activity of perennial plants in relation to the results you get from transplanting and seeding. For instance, my apple trees began blossoming a full three weeks later this year than average. Since they are responding to the actual growing conditions, they are an indicator that planting and sowing of spring crops should be three weeks later than average. Carefully maintained records of your observations in the garden are of far more use to you as a gardener than any amount of dogma, or theory. Your garden is unique, in its micro-climate, insect, fungus, bacteria and weed populations. By careful observation and gentle guidance, you will be able to insinuate your influence into the constantly changing relationships between all these organisms. Try to dominate them and you will lose the battle, as conventional growers so often do. Instead of having Nature's support, you will reap a harvest of a bewildering variety of new pests and diseases, decreasing soil fertility and self-loathing at your lack of ability to achieve your goal: domination. When you adopt the organic approach, you will see the various organisms in your garden as unique and important for the roles they have to play. Feed the soil and its micro-organisms and not the plant. Discourage the weeds and undesirable insects, rather than try to destroy them. If this means donating 5% of your crop to Nature, so be it. Your garden will reward you with a bounty of produce and peace of mind.

Crop Seeds per gram Min Temp (C) Temp Range (C) Opt Temp (C) Max Temp (C) Space between rows (cm) In row space (cm) Depth to sow (mm) Weeks to mature
Asparagus 50 10 16-30 24 35 50-90 20-40 20-30 100-150
Beetroot 60 5 10-30 30 35 30 8-10 20-25 9-12
Broad bean 1 (1) (1) (1) (1) 60 15 50-75 18-24
Broccoli 300 (2) (2) (2) (2) 75 50 10-15 10-16
Brussells sprouts 300 (2) (2) (2) (2) 90 60 10-15 18-25
Cabbage 300 5 7-35 30 38 60 45 10-15 8-16
Chinese cabbage 300 (2) (2) (2) (2) 60 30 10-15 9-10
Canteloupe 40 16 24-35 32 38 120 120 25-50 11-14
Capsicum 150 16 18-35 30 35 45 40 10-15 12-16
Carrot 1000 5 7-30 27 35 30 6-7 10-15 10-15
Cauliflower 300 5 7-30 27 38 90 50 10-15 12-26
Celery 3000 5 16-21 21 30 35 25 10-15 20-24
Chicory 500 (6) (6) (6) (6) 30 20 10-15 10-16
Cucumber 40 16 16-35 35 40 100 100 20-40 9-12
Egg plant 250 16 24-32 30 35 100 50 10-15 14-18
French bean 4 16 16-30 27 35 45 10 25-50 10-14
Kale 300 (2) (2) (2) (2) 50 30 10-15 8-10
Kohl rabi 300 (5) (5) (5) (5) 40 20 10-15 10-12
Leek 300 (3) (3) (3) (3) 40 12 10-25 20-24
Lettuce 800 4 5-27 24 30 30 30 10-15 9-12
Onion 200 4 10-35 24 35 30 6-8 25-50 18-30
Parsley 800 5 10-30 24 32 30 15 10-15 10-12
Parsnip 300 4 10-21 18 30 30 6-8 10-15 18-25
Pea 5 5 5-24 24 30 40 6-8 30-40 8-12
Potato * (4) (4) (4) (4) 75 30 75-100 16
Pumpkin 5 16 21-32 35 38 1-200 1-200 25-50 14-22
Radish 100 5 7-32 30 35 20 5 10-15 4-5
Silverbeet 60 5 10-30 30 35 30 15 20-25 8-12
Spinach 100 4 7-24 21 30 30 15 15-25 7-10
Squash 5-10 16 21-35 35 38 100 100 25-50 8-16
Swede 300 (5) (5) (5) (5) 35 15 10-15 14-16
Sweet corn 5 10 16-35 35 40 100 30 25-50 10-12
Tomato 300 10 16-30 30 35 90-100 45-50 10-15 12-18
Sweet potato * (7) (7) (7) (7) 75 30 90-120 26-34
Turnip 300 5 16-40 30 40 30 7-8 10-15 8-10
Watermelon 10 5 21-35 35 40 180 150 25-50 12-14

(1) Not known, similar to pea.

(2) Not known, similar to cabbage.

(3) Not known, similar to onion.

(4) Not known, sown after any chance of frost.

(5) Not known, similar to turnip.

(6) Not known, similar to lettuce.

(7) Not known, frost-free areas only.

* Not true seeds. Tuber pieces should be approximately 50 gms each.

Crop Season Temperature Range Optimum Temperature Crop
Cool Season Crops 0C+ Not known Asparagus, rhubarb.
7-29C 13-24C Chicory, chive, garlic, leek, onion, salsify, shallot.
4-24C 15-18C Beetroot, broad bean, broccoli, brussells sprouts, cabbage, collard, horse radish, kale, kohl rabi, parsnip, radish, silver beet, sorrel, spinach, swede, turnip.
7-24C 15-18C Artichoke, carrot, cauliflower, celeriac, celery, chicory, Chinese cabbage, endive, Florence fennel, lettuce, mustard, parsley, pea, potato.
Warm Season Crops 10-26C 15-21C French bean.
10-35C 15-24C Sweet corn, New Zealand spinach.
10-32C 18-24C Pumpkin, squash.
15-32C 18-24C Cucumber, canteloupe.
Hot Season Crops 18-26C 21-24C Sweet capsicum, tomato.
18-35C 21-29C Egg plant, hot capsicum, okra, sweet potato, watermelon.

Tabular data largely based on Handbook for Vegetable Growers by James Edward Knott, John Wiley & Sons, New York, 1957.

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Jonathan Sturm 2003 - 2011

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