here's some advice and tips from Mandalaseeds' Troubleshooting Guide (
http://www.mandalaseeds.com/html/gtg.html). They also have a few pics that may too:
Seeds did not germinate:
The first step is to look at what happened to the seeds.
There are 3 possibilities:
a) the seeds all look the same like when you planted them (intact, healthy colour)
b) some or all seeds are intact, but have noticeably changed colour and are darker; some may also have a whitish substance coating the rounded end
c) some or all of the seeds cracked open and the taproot appeared - but there was no further growth
Possible causes for:
a) Healthy & intact seeds don't germinate if the substrate is too dry. This could mean that it was too dry from the start, or that the substrate dried out before the seed could absorb enough moisture to trigger germination. Open some of the seeds to check the embryo. If it is healthy, white and firm then the seeds required more water to germinate.
Second probability is that the seeds are damaged from frost.
b) Dark seeds indicate fungal attack. A whitish substance is visible fungal mycelia. Fungus spreads under cold, wet, & anaerobic conditions. Several combinations of factors can lead to seeds rotting: poor soil quality (infected, bad pH, or high EC), pre-soaking seeds in water, substrate is too wet, substrate is in a cold environment, and/or excessive high humidity caused fungal growth in substrate (due to humidity dome/propagator, pots covered with plastic, poor ventilation).
Open some of the seeds to check the embryo. In rotted seeds the embryo is soft, yellowish or almost like liquid.
c) This can happen for the same reasons as in b). But there can also be other factors involved. If a heating mat was used the substrate may have been heated up too much. In rockwool a high EC can kill the emerging seedling. Check the EC of your substrate and make sure your EC meter is functioning correctly. A sudden dry spell in the substrate is also lethal at this stage.
Also check your water quality. In some areas municipal water is extremely low quality. It can have an excessively high salt level and can be contaminated with minerals/heavy metals which stunt plant growth. High levels of chlorine and fluor are dangerous. You can smell chlorine - let it evaporate before use by filling a bucket with hot water. If you are in doubt about your tap water buy bottled mineral water (without gas). The pH should be adjusted to 6.5 for soil and pH 5.6-5.8 for rockwool..
Watering with organic teas or various other products is definitively counterproductive. During germination and seedling stage you should use pure pH adjusted water.
Other factors:
Jiffy's, peat pellets, and other types of starter plugs with an alkaline pH inhibit germination in cannabis seeds. Some substrates such as coco coir may also be pre-fertilized and have a high EC (salt) level Untreated coco coir contains toxic levels of sodium and chloride. Or they could have been treated with fungicides and pesticides. If you have used a particular product with poor results you should stop using it and switch to rockwool or soil.
Seedlings
Some or all seedlings grow weak and tall:
The major cause is lack of light. The seedlings are stretching in search of light. This leads to elongated and weak growth. Give your seedlings as much light as possible. Move them closer to the lamp. Put them under an HPS lamp if available. If you are growing near a window move the plants to the sunniest spot or supplement grow time with a lamp. Outdoors you should also provide as much light as possible. Support the seedlings with a stick or looped wire while they regain strength. As soon as they have sufficient light they will grow vigorously.
Some or all seedlings fell over and died:
This is usually caused by a fungal disease called "damping off". The cause is infected soil, waterlogged substrate, high humidity...any conditions that promote fungus. The fungus attacks the soft tissue in the stem which withers at the base or midway. The seedling collapses and dies. Another possible cause is that the seedlings died from lack of water or a high salt level in the substrate (which basically has the same effect of drying out the plant). Seedlings have only a small amount of roots and few leaves. They cannot retain much water and quickly dry out. High humidity in the grow space does not compensate for a desiccated substrate. Your soil/rockwool has to be moist enough to sustain healthy roots and provide water to the plant. Photo shows “damping off”.
Outdoor frost can kill seedlings overnight. Keep your seedlings indoor until there is no danger of sudden frost.
Seedlings cannot open their first set of leaves:
Sometimes the seed hull and the inside skin is still attached to or enclosing the leaves. This happens if the seed was not planted deeply enough. Usually the seed hull is detached as the seedling emerges through the substrate. Spray the seed hull with mineral water and wait 1/2 hour for the moisture to soften the dry skin and soil residues. Then gently and slowly pull it off from the leaves. If it does not move easily spray more water. It is very important to remove it carefully because if you tear off the leaves the seedling dies.
Recommendations
We hope that this guide has been helpful in detecting the probable cause for any problems that you have encountered. The next step would be to run a test under improved conditions. For this purpose it is best to germinate just a few seeds as a trial. If everything goes well you see the results within 7+ days and can germinate the remaining seeds with confidence. A novice grower will also find this helpful advice before losing all of the purchased seeds on a set-up that requires modification!
Hydroponics
If you are new to cannabis growing it is not advisable to start with hydroponics. Don't make your first cultivation experience unnecessarily complicated! In hydroponics you have to constantly monitor EC and pH, choose the correct nutrient formulas and feeding schedule, clean and flush your system, invest in expensive equipment, etc. If you are insecure about germinating and growing in rockwool or other hydroponic substrates, switch to soil or start with a small test group to gain experience.
Especially with our genetics you will find growing on soil very easy and rewarding. It is highly probable that any benefits you may be expecting from hydroponics, such as a higher yield, will be much simpler and securer to achieve with a straightforward soil cultivation!
Soil
Choosing the correct soil for germination and seedlings should not be difficult. However, some growers feel overwhelmed and insecure by the seemingly endless jungle of products, whilst others may live in countries with a very small and unsatisfying range of products. Please refer to our SOIL GUIDE for tips and recommendations.
Hope this helps ...
