Growing Marijuana Seedlings: getting your cannabis crop off to a great start
see bottom of the page for Campo’s Choice Picks to help you get your seedlings off to a great start!
Whilst buying good Cannabis Seeds provides you with the genetic capabilities of your cannabis plant, growing marijuana seedlings well enables these traits to be realized. Limiting factors at this crucial time in development will have repercussions for the mature plant – or more likely, kill it off whilst it is at a delicate phase. The seedling stage lasts from 1-4 weeks, so you have only this amount of time to get it right!
It’s important to give marijuana seedlings a constant atmosphere with moderate humidity, warmth (21ºC) and reasonable light quality – therefore even if you intend to grow outdoors, it is worthwhile investing in a (heated) propagator and even a small CFL light to enable a healthy start to your plants.
A humid atmosphere enables the seedling to absorb water through the leaves whilst its root system is as yet immature, thus speeding up the growth rate of the marijuana seedling (85-90% rH).
Remember that these plants would naturally be growing in spring time in warm climates. 21ºC simulates that fact.
Not enough light and obviously the marijuana seedling will struggle to photosynthesize and thus grow. (see stretching): too much light however will overpower the delicate root system as the plantlet fails to absorb enough water and nutrients to maintain the transpiration rate. A natural indirect light is preferred for the first few sets of leaves, after which CFL lighting is very useful. These fluorescents can be hung 5 cm from plant tips to avoid stretching.
Seedlings should receive a minimum of 18 hours light a day, but can cope with 24 hours.
Always use a “soft” water (e.g. distilled or mineral) with a pH OF 5.5 – 6.5. If you have to use tap water, allow it to stand for 24 hours to allow the chlorine to evaporate. Whichever you use, let the water come to room temperature to avoid shocking the marijuana seedling.
Do NOT over water – this is a common cause of “damping off”.
Especially with marijuana seedlings it is vital that the growing medium allows oxygen to get through to the fledgling root system. Soil grown seedlings need to be in either a specialist seedling mixture with plenty of perlite or sand to allow good drainage. Rockwool must not be allowed to be sodden as this too will prevent oxygen reaching the roots and “drown” the plant.
Note also that any soil used should not be rich in nutrients as these will cause nutrient burn and inhibit the rooting process.
Marijuana seedlings are vulnerable to over fertilization (nutrient burn), whilst at the same time the nutrient free nature of most seedling mediums necessitates their addition before long. To avoid over fertilization, use either a specialist seedling feed or dilute a cannabis feed to ¼ strength.
Whilst not a fertilizer, it can be a good idea to give a diluted amount of RootBoost or similar to enable good root development in your young plants.
Marijuana seedling problems
Fungal disease whereby stem becomes floppy and marijuana seedling dies. Avoid by making sure growing conditions are neither too wet nor too humid.
See nutrients above
Whilst some strains (especially those with a sativa base) are more likely to stretch – or appear to – stretching should be avoided in marijuana seedlings as it leads to lanky growth with weak stems in mature plants. It also has the effect of a prevalence of small buds as opposed to good dense ones.
Stretching can be caused by a number of reasons:
- Poor light: seedlings will stretch towards any available light source if they are not receiving enough.
Campo’s Choice Picks to help you make sure your grow room gets off to a great start in 2013!
Another great product from Hydrofarm (these guys really do seem to get the best customer reviews), this “germination station” or heated propagator will help get your seedlings off to the best start.
- Germination station with electric heat, humidity control and 72-cell seedling inserts
- Provides gentle warmth to the planting bed; controls humidity under 2-inch dome
- Humidity dome with dual vent points for optimal airflow
- Includes seed starting booster, instructions with growing tips
- Watertight base tray measures 11 by 22 inches
Its reduced from
$34.99 down to $24.88 on Amazon.com and that sounds like a fair price to us!
Use withHydrofarm MTPRTC Digital Thermostat For Heat Mats which is $25.29 and will enable you to provide a specific controlled temperature for your cannabis seedlings.
What we’d really recommend though – unless you are growing with LEDs is that you invest in a decent T5 system. This will prevent over stretching which occurs when young plants seek out light from an insufficient source and also heat burn from too hot a light source (eg too close a HID growlight).
We are going to recommend the Hydrofarm JSV4 4-Foot Jump Start T5 Grow Light System ($63.99) as if you buy all 3 items together, you get them for $114.16. The T5 system is described as a great light for the money, and one which will keep you producing healthy marijuana seedlings for years to come. There are a few quibbles about flimsiness, but this version is the more sturdy of the ones produced and sold by Hydrofarm, and it features on Amazon’s Best sellers list, so it cant be all wrong.