Growing organic maize

organic maize

Maize is the organic farmer's dream crop. It grows rapidly, it produces a lot of drymatter and equally important, it produces a lot of energy in the form of starch. To ensure crop success there are a few steps which need to be followed. These are outlined below:

1. Paddock selection

Successful establishment of a maize crop relies upon following all the recommended steps at the correct time. If possible, select your paddock in the early autumn. Walk the whole area and check for the following:

  • 1.1 Perennial grass weeds (e.g. couch and mercer grass).
    If perennial weeds (e.g. couch/twitch, mercer grass, kikuyu) are not controlled they can cause a significant reduction in maize yield. Avoid using paddocks which have a major perennial weed problem.
  • 1.2 Drainage.
    Maize does not perform well in waterlogged soils. Water logging can also encourage weeds like willow weed to invade the crop. This can reduce maize yield and also impact on silage quality, palatability and stock health. Drain any areas where water ponds develop to allow earlier cultivation, better weed control and reduction in nutrient leaching.

2. Soil test

Soil test to determine the most suitable fertiliser and lime input. Fertiliser requirements will vary greatly depending on the history and fertility status of the paddock. Long-term dairy pastures which have had a history of effluent application may require no fertiliser while continually cropped paddocks or run-out sheep and beef farm pastures sometimes require capital fertiliser applications. Soil core to the depth of cultivation - normally 150 mm and up to 300 mm on peat soils. Increase lime application in areas where contour correction is required especially on heavy soils and peats.

Fertiliser: Organic certified fertiliser must be used. Fortunately the two key minerals maize needs for growth (potash and nitrogen) are available organically at reasonable prices. Sources include muriate of potash (MOP), chicken litter and dairy shed effluent.

3. Maize hybrid selection

It is important to choose the correct Pioneer® brand maize hybrid for your area. Your local Pioneer Representative will have a variety of hybrids that better suit growing maize organically, contact them for regionally appropriate advice. Some important factors to consider include:

  • 3.1 Comparative relative maturity (CRM).
    This is an indication of the growing period from planting to harvest. The actual crop growing period will vary according to the amount of heat the crop receives (i.e. spring, summer and autumn temperatures) during the season. The warmer the season, the shorter the period from planting to harvest. See the Pioneer® brand maize silage catalogue for average planting and harvest dates for Pioneer hybrids in your area. Note: The comparative relative maturity of the hybrid is not the number of calendar days from planting to harvest.
  • 3.2 High total DM and grain yield.
    Hybrids must have a high total drymatter yield as well as a high grain yield to achieve maximum metabolisable energy yield per hectare. Grain yield is important as grain contains 70% more metabolisable energy and greater carbohydrate levels than stover (the green part of a maize plant).
  • 3.3 High population adaptability.
    High plant populations are necessary to ensure high silage yields. All Pioneer,® brand maize hybrids have been fully tested for their adaptability to high populations and fulfil this requirement. It is important to plant as high a population as possible to maximise suppression of all developing weeds.
  • 3.4 Drought tolerance.
    If planting into paddocks with drought prone soils choose a maize hybrid with a good drought tolerance rating.
  • 3.5 Plant shape.
    Light suppression is really important to prevent weed growth. Choose a hybrid with more prostrate rather than erect leaf shape. Your local Pioneer Representative can assist you in identifying more prostrate hybrids.

4. Choose your ideal planting date

Maize loves heat! Aim to plant organic crops when the soil temperature is consistently above 14°C and day temperatures are above 18°C. For most areas this will be late October or early November.

5. Cultivate as soon as possible

Once the ideal planting date has been chosen, begin cultivating at least six weeks prior to this. The aim of the cultivation process is not only to prepare a seedbed to plant into but also to reduce the weed bank and kill harmful insects (e.g. Argentine Stem Weevil, Black Beetle and Greasy Cutworm). You may need to cultivate the ground three or four times before planting. Check the ground regularly and when sufficient weeds have germinated, run a spring-tine cultivator or some other similar implement over the ground. Aim to have a soil crumb size about the same size as the seed.

6. Contour and lime

If contouring is not required apply lime just after the initial cultivation. If contouring is required, undertake cultivation and apply lime when shaping is completed. Apply extra lime where drain banks or humps have been removed, especially on peat or clay soils.

7. Fertiliser

Spread and incorporate the fertiliser dressing at least a week before planting.

8. Final cultivation

If more than 24 hours have elapsed or it has rained since the last pass of the cultivator, make a further pass with a surface cultivator (e.g. rotor-tiller), before planting. If the soil is very dry and there is still a significant number of weeds present only cultivate the soil very lightly and shallowly so that you kill the weeds but prevent too much soil moisture loss.

9. Planting

Maize hybrids for silage must be precision planted. Choose a competent contractor with well-maintained machinery and drives at the speed recommended by the drill manufacturer.

10. Insect control

Organic maize is limited when it comes to insect control. Starving them through effective cultivation and a long fallow period is the most effective means of ensuring the young maize seed is protected.

Greasy Cutworm: Greasy Cutworm moths will lay eggs in the months prior to planting. Infestations are sporadic but tend to be more common in weedy paddocks dominated by docks and chickweed. When these paddocks are planted, small caterpillars can persist through short cultivation periods. Larger caterpillars cut and consume small seedlings when the plants are 50-300 mm high. Later infestation does not kill the plant but may weaken the base of the stem and cause lodging.

Infestation can be avoided - Cutworm caterpillars may be damaged or starved by cultivation and removal of plant matter seven or more days prior to planting.

For information about insect control in maize crops: refer to "Plant Protection in Organic Arable and Vegetable Crops - a growers resource", Crop and Food Research publication (2005).

11. Weed control

Post emergent weed control is best achieved by:

  • 11.1 Pre-plant cultivation to reduce the size of the weed seed bank.
  • 11.2 Choosing prostrate leafed maize hybrids and planting them at high populations.
  • 11.3 Inter-row cultivating when the plants are knee high.

12. Crop checks

From about six days after planting check crop emergence. Full emergence normally occurs 7-14 days from planting depending on temperature. Walk the crop every second or third day checking for insect and bird damage and weeds.

  • 12.1 Greasy Cutworm. The symptoms of Greasy Cutworm in the crop are plants that have been cut off at ground level. Greasy Cutworm is a dark coloured caterpillar that feeds at night and burrows down into the soil during the day.
  • 12.2 Bird damage. If you find small seedling plants pulled out of the ground with the roots still attached, it is probably bird damage. Birds can be attracted to the area by seed left on the surface of the ground when the planter lifts at the end of each planter run or on tightly turned corners. If you note seed on the ground at planting, draw your contractor's attention to the problem. If ducks are a problem and soil temperature is 14°C or higher, adjust the planting depth to 65 mm.
  • 12.3 Seedling weeds. Inter-row cultivate just prior to canopy cover.

B. Harvesting and ensiling maize silage

The secret to making good silage is to ensure that it is harvested at the right time, compacted into an air tight stack and then kept air tight until it is ready to be fed out. It is important to follow the correct procedure in order to make great maize silage. This is:

1. Organise your contractor

Ensure you make contact with your chosen contractor earlier rather than later. Get them involved with the whole harvesting process. Make sure that they understand that your maize is organic maize to ensure there are no mistakes made. On an organic farm, outside contractor's are required to have cleaned their equipment before entering the property. Giving your contractor plenty of notice of your job will allow them to plan your work after a normal clean down procedure. A standard "contractor" form needs to be completed each time a contractor brings equipment onto the property to confirm their machinery was cleaned - your organic certifier can provide you with a template.

2. Choose the site of your stack

Many farms already have a bunker available to use. If there isn't one on-farm or if maize is stored in a bun, choose your stack site well. It needs to be on free draining ground, close to where the maize is going to be fed. It also needs to be a reasonable distance from walls, fences, drain banks etc. to ensure stack tractors can run off the stack when stacking.

3. Timing of harvest

The ideal time to harvest your maize for silage crop is when the whole plant drymatter is between 30-38%. Harvesting a crop too early will result in a yield sacrifice. High drymatter losses can occur as plant fluids run from the stack or bunker taking away valuable sugars. Late harvest may result in a loss of quality as plant stover (leaf and stalk) increase in fibre and become less digestible. Dry crops are also difficult to compact properly. Please note: Bulletins giving further details on the harvesting and storage of wet and dry maize crops are available. Call Pioneer toll-free on 0800 PIONEER (0800 746 633).

In a crop that is still green (i.e. not frosted or drought stressed), the first sign that harvest is approaching is the husk covers turn slightly yellow-brown. There are several ways in which you can determine when your crop is between 30-38% whole plant drymatter. Please note that the following guidelines should only be used to determine if the crop is ready to harvest.

4. Milk line

The whole plant drymatter can be estimated by looking at the milk line of the grain. To check whether your crop is in the range of 30-38% drymatter:

  • 4.1 Take a cob from a plant that is at least 20 rows into the crop. The plant that you take the cob from must be in a uniformly planted row.
  • 4.2 Break / snap the cob in half and discard the end of the cob that was attached to the plant.
  • 4.3 Hold the point of the cob downwards and remove a kernel from the "snapped" end.
  • 4.4 Keep the kernel the same way up as when you removed it from the cob. Slide your fingernail along the length of the kernel starting at the flat (dented) end of the kernel. 


  • 4.5 Note the point where the solid starch ends and the liquid milk begins. The hybrid will be ready for harvest when the milk line is two thirds of the way down the kernel (see Fig 1).
  • 4.6 The milk line test is only indicative that harvest time is near. The only sure way to test plant drymatter is though the microwave test or by sending a plant to a suitable lab (see the next two points).

5. Plant moisture content

The moisture content in the plant (leaves and stem) can vary considerably. This is especially evident immediately after an extended dry period following rain. Plants re-hydrate and can hold significant amounts of moisture in the period immediately after a rain event ends a dry period.

To check the content of moisture in the maize stalk, grasp the stalk at the inter-node below the cob and pull the top of the maize plant over so as to fracture the stalk.

Lift the top part of the stalk back to the upright position and twist the top portion of the stem noting the amount of fluid evident where the stalk is fractured. If there is only a small amount of moisture showing between the stem fractures then the milk line drymatter percentage guide will hold true. But if there is a significant amount of fluid and it runs down the stem, downward drymatter percentage adjustment will need to be made.

A drought stressed crop may have all leaves up to the cob browned out and no moisture in the stem. In such situations the drymatter percentage of the crop can be higher than the milk line indication on the kernels.