In this article, we’ll show you how to troubleshoot the most common microgreen growing problems.
It has been found that temperatures between 18-24°C are most favourable for microgreen growth. Temperatures above this can increase disease pressure, such as damping-off disease or inhibit germination in some varieties. While temperatures that are lower than this can result in lower evaporation rates. A solution for this is to grow your microgreens indoors or in a greenhouse. Growing microgreens on a windowsill will provide your microgreens with a suitable light source. Indoor growing allows you to properly control the temperature, by either using a fan or reverse cycle air-conditioner.
Damping off disease
Damping off disease refers to the destruction of seedlings by pathogens. These pathogens are common in soils in both tropical and temperate regions and almost all fruits, vegetables and crops are susceptible to attack. Weather and soil conditions can also contribute to the disease’s development. The most common pathogens that are experienced in Australia are Pythium species and Rhizoctonia solani. Others are Phytophthora, Fusarium and Aphanomyces.
Symptoms of damping off
There are two types of damping-off that a plant can experience. Pre-emergence damping-off refers to the rot of seeds or seedling sprouts prior to them emerging from the soil. While post-emergence damping-off occurs when the plants emerge from the soil, as a soft decay within the taproot or rootlets which cause the seedlings to collapse. When R. solani infects a plant, this can lead to a water-soaked, sunken lesion at the ground level, which causes the plant to fall over. Plants can survive this but will be stunted and affected areas will typically show uneven growth.
Seedlings that have more rigid stems (e.g. cabbages) won’t fall over, but their stem will be thin, discoloured and possibly bent or twisted without it breaking, this is why the disease is referred to as ‘wire stem’.
How does it spread?
As previously mentioned, Pythium species can be found in soil or water, where they live as saprophytes (live on dead or decaying organic matter), or as parasites and attack through the fibrous roots of the plants. Different species have adapted to be found in different climates. These pathogens thrive in moist soil and when temperatures are unfavorable to the host plant. Both Pythium and R. solani can be spread by rain, irrigation, water splash, contaminated tools, soil or potting mix, and infected plants.
A way to mitigate the likelihood of infection is to raise your seedlings in soilless potting mix on elevated benches. Preventing contamination of treated soil by avoiding splashing water, using contaminated tools or storing in dirty areas could also help this. Avoid excessive watering, and don’t overcrowd your seedings. It is also recommended to treat the seed with a weak solution of hydrogen peroxide before planting.
Cleaning your trays properly before use is an important step to ensure healthy microgreen growth. The following details how to properly clean and sterilise your growing trays.
- Remove any left over debris with a dry scrub
- Use a dry brush, cloth or wipe, to clean the trays from any left-over soil, roots or other debris. Clean both the top and underside of the tray and drainage holes.
- Clean with soap and water
- Following the dry scrub, clean your trays with soapy water and rinse, ensuring the drainage holes are clean.
- This is the most important step as it removes soil and other residues, such as germs, fungus and disease that can all impact microgreen growth
- This can be done by using plain white vinegar. Most household vinegar has a 5% strength, meaning you won’t have to dilute it. Spray onto the surface of a tray and allow it to sit for around 10-20 minutes, then wipe or rinse off.
- The other option is to use hydrogen peroxide, you can buy a 3% mixture from most supermarkets which is environmentally friendly, as its two atoms of hydrogen and two atoms of oxygen which occur naturally in the environment. It is safe to use, compared to chlorine-based chemicals. It’s recommended that you pour the mixture into a spray bottle, spray it onto the surface of your trays and let it sit for around an hour, then wash it off with water.
- There are a few safety tips for using/storing your hydrogen peroxide as it is still a corrosive and combustible chemical. These are:
- Handle with care, by wearing gloves or goggles
- Don’t store near a source of heat, combustible equipment or flammable liquids
- Store in a container suitable to corrosive chemicals (plastic is ok if it is a 3% mixture, if you’re using a higher %, dilute it with water)
- It quickly degrades when exposed to light, therefore store it in a dark container or cupboard to avoid this
- Store out of reach of children and pets
- Dry off
- Allow your tray to dry, they you’re ready to plant!
Growing media are often formulated by blending different raw materials together, to achieve a good balance of air and water holding capacity for plants to grow in. Therefore, if you get the correct media, this can be greatly beneficial to your plants. Our recommendation is to use coir peat. Coir peat is made from the fibrous material inside a coconut, between its outer coat and fruit middle. There are two types of fibers that can make coir and are either brown or white. Brown coir is made from mature, ripe coconuts and is stronger but less flexible. While white coir comes from pre-ripe coconuts but are more flexible and less strong. The most suitable coir for hydroponics is brown as it’s processed more after its initial harvest.
Using coir peat in hydroponic gardening
Coir handles like regular potting soil and makes transitioning from soil gardening to hydroponic gardening very easy. When searching for the right type of coir for your purpose, make sure you find one suitable for hydroponic gardening, as this will have sodium and potassium removed, providing a completely nutrient-neutral medium. This will allow you complete control over your plant’s nutrient uptake. While the ornamental version of coir can be inexpensive, it is unsuitable for hydroponic and food production as it generally has higher salt levels. Brown coir has been processed more, therefore will act as a support medium and will present less risks of introducing pests to your hydroponic garden.
Recommended potting media mixes
Making your own potting mix can be an effective way to develop your own mixes for specific growth goals or different plants. It gives you the opportunity to be creative, know your plants and their preferences. Potting media, which typically is coarser than garden soil, is often used in container gardens and in trays for sowing seeds.
Primary potting media are sphagnum peat moss, as it has a coarse texture and allows for good aeration through the soil, while still providing a strong water holding capacity, which won’t dry out your soil. However, be careful not to add too much peat moss as it can restrict soil drainage. You should also moisten the moss before mixing with other ingredients as it can be difficult to wet.
Coarse, sharp, or builder sand, which is typically used in construction, is a great ingredient for potting media. Similarly, to peat moss, it improves drainage and aeration but won’t improve your medias water-holding capacity. Be careful not to add too much sand as it can be heavy.
Perlite is also used in both peat-based and soil-based potting media, as a replacement of sand. Perlite is a naturally occurring mineral, which exists as a type of volcanic glass. Like sand, it allows for good drainage, but is lighter and holds more air. There are a few disadvantages to using perlite, such as the fact that it can float to the top of the medium when it is watered, it has difficulty retaining water and it should be moistened before mixing into other ingredients to reduce dust.
Soilless potting media mixture
- 60% soil-building material: It is recommended peat moss or coir peat is used in a soilless potting media as they’re light and absorbent but can also maintain water.
- 40% nutrients and aeration material: Use 20% perlite and 20% sand to add drainage and ensure the soil is airy and open.
Soil-based potting media mixture
- 50% coir peat
- 50% organic soil mix (can be store bought), however if you choose this option you must ensure it meets Australian standards. A few things to look for when choosing your soil mix are:
- Choose the freshest stock as the longer the mix has been in the bag, the more microorganisms will have consumed the nutrients within it.
- Choose the appropriate level of water-retention, match the mix to the type of plant you’re growing.
Adding ground limestone and fertilizer to soil or soilless potting media
It can also be useful to add small amounts of ground limestone and fertilizer to your media. These ingredients can be blended in a separate container and added to your media. Fertilizer will help with nutrient supply; however, you must ensure the correct pH is maintained so the nutrients can be available for plant roots to absorb. The range in which nutrients are available to plants is between 6.0 and 7.0, on the pH scale. To do this, you can buy at home testing kit and use soil samples from just below the surface. Another alternative is by using an electronic pH meter, which comes with a probe that can be inserted into the soil for an accurate measure.
Depending on the length of time plants are in containers, it can be beneficial to add supplemental fertilizers to soil-based media. Clay or mineral content found in garden soil can provide nutrient retention and water-holding capabilities. Therefore, soil-based media typically provides enough fertility in comparison to soilless media. When making soil-based mixes, the pH should be adjusted according to soil test results. A slow release complete fertilizer is useful for both soil and soilless potting media at rates that can be found in the fertilizer packaging. This will help ensure nutrients are available for your plants year-round.
Whether you’re using soil-based or peat-based media, pH is often too low (<6.0), therefore it will need to be adjusted. This can be done by using ground calcite limestone or agricultural lime, which raises media pH and contains calcium, which can even help to strengthen your plants cell walls. Dolomitic limestone can also be used and supplies magnesium and calcium to your plant. It is recommended to add four tablespoons of limestone to your media.
Soilless or peat-based media can also require an adjustment to the pH levels, typically upward to be between 6.0 and 7.0. To do this, you can purchase a slow release fertilizer and limestone to achieve this. After adding fertilizer and limestone to your soilless media, it should be sifted through a small (approx. 1.5cm) wire to break any large clumps. Media that you’re using to germinate seeds should be sifted through a smaller wire (0.5cm), to produce a finer texture. Finally, remember to moisten your media before sowing or planting.
Following their blackout period and germination, your microgreens should now be placed under light conditions for 5-8 hours a day. They will also need to be watered regularly to ensure healthy, efficient growing. It is recommended to water them every one to two days, or any time the soil begins to dry out. A sign that they need water is when the green or early cotyledon (leaves) start to droop.
Ensure you do not completely soak your microgreens as this can lead to overwatering and killing them. It may be beneficial to water from the bottom up. This can be done by placing your microgreen trays in a larger tray of water, so they absorb the water through the drainage holes in the bottom of the container. Don’t leave it in the tray for longer than a few minutes as this can lead to oversaturation, causing mold or disease. A sign of overwatering can be when your microgreens begin to look yellow and won’t turn green (however, this can also be a sign of not enough sunlight).
If you can’t water using the bottom-up method, ensure to water around your growing microgreens rather than directly onto their leaves as this can damage the growing plant.
For hydroponic growing microgreens, ensure that the areas between the growing pad and edges of your container receive regular water when the pad starts to feel dry. Don’t pour directly onto the pad as this can dislodge the seeds.
This is another common problem that microgreen growers face. Proper ventilation is necessary as it supports plant transpiration and avoids depleting your grow rooms CO2 supply. Evidence of insufficient airflow can be through your plants smelling off, beginning to wilt, or mold forming.
Ventilation fans can be a useful tool in helping with circulation as they maintain room humidity and temperature. Fresh air also helps to fight pests, mold and rot issues. A small oscillating fan can do the job; however, you must ensure that the air can still circulate through the room, and warm air can escape. Depending on the size of your grow room, you may also need a few fans around your room. Be careful not to place the fans too close to your microgreens as this can damage them, similarly to outside wind causing windburn to plants. Extractor fans can also be used in larger rooms, if necessary. These systems will remove old air, while bringing in fresh air.
Dehumidifiers are another popular choice amongst microgreen growers, this is because they remove the moisture that the microgreens produce via transpiration and will return dry air.