4 | Seedling Care

2 Sep 2020
by Francois

Congratulations! Now that your seeds have germinated, you have successfully completed the first step – getting them off to a great start! Let’s keep building on this success.

Maintenance of seed starts

Watering – Once your seeds have germinated and you see the first leaves appear, it’s time to decrease their watering frequency. Keeping the top layer consistently moist was only necessary for germination – in fact, now that they have germinated, excessive moisture will only cause problems. Excessive moisture can lead to fungal growth and “damping off”, which causes the seedling to rot and die. Only water the trays when you see that it is necessary. There are a couple of clues that you can use to determine if your trays need water. I will list them in order of appearance, i.e. what you notice appearing first means the tray has more water and what you notice appearing last means the tray has less water:

  1. The top germination mix / vermiculite layer will dry out
  2. The tray will feel less heavy (feel the weight before and after watering to get a feel for it)
  3. The mix in the cell will pull away from the sides of the tray

When your tray reaches nr 3 it is already way too dry and your seedling will have suffered, most probably visibly so, i.e. drooping leaves. Ideally you want to water your tray when you notice the weight has decreased markedly (nr 2), but before the soil retracts from the sides. Also note that, at this stage in the seedling’s growth, when you water them, it is important to give them enough water so that it reaches the roots all the way down at the bottom of the cell.

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Sufficient light – Your seedlings need enough (indirect / filtered) light during this initial growing stage. If you see them becoming very thin and tall (grower’s lingo for this is “leggy”), it means they are getting too little light and growing tall in search of more light. If your growing area does not have enough light, you can put your trays outside in the direct light, but only in the morning and only for a short while. Start with 30 mins and over the course of a week, work your way up to around 2-3 hours of morning sunlight. At this point, they should stop growing taller and start to bulk up.

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Fertilising – As mentioned earlier, following germination (root and leaf growth), the seed’s internal food storage will have been depleted and the seedling can do with some nutrients. You can use any commercial seedling fertiliser which will contain macronutrients nitrogen, phosphorus and potassium roughly in a 2:1:2 ratio, as well as some micronutrients. You can use a 5L pressure sprayer to feed the seedlings with. Feeding them should replace a regular watering session and always dilute fertiliser as directed. Feeding your seedlings 1 – 2 times per week should be sufficient. If your seedlings are too dry, do not give them fertiliser, but rather water them first and fertilise at the next scheduled watering. (When your direct sown seedlings have about two sets of leaves, you can start fertilising them on a weekly basis as well. Since they are in soil that already contains a lot of nutrients, they do not need feeding as often as the seedlings that are growing in the trays).

Algae and mold growth – Algae growth is unfortunately unavoidable at times. Excessive nutrients, moisture and heat are ideal circumstances for algae growth. Be sure to stick to a fertilising schedule. Twice a week should be sufficient. Also, larger seedlings will absorb added nutrients faster than smaller seedlings, so adjust your fertilising schedule (or the amount of fertiliser) accordingly. If you control the amount of nutrients and the moisture level, algae growth should be limited. It should be noted that although algae growth isn’t deadly for your seedlings, it does form a film on the surface of the cells which makes it more difficult for water to penetrate and fill the entire cell.

WATCH OUT FOR
Damping off disease – A combination of pathogens is responsible for this disease, which proves to be detrimental to seedlings. White and / or grey fungal growth will be visible just above soil level where seedling stems will reduce in thickness, followed by the wilting of the seedling.
This disease starts and thrives during prolonged cold and wet periods and where there is an excess of nutrients. Keeping your trays moist (but not wet) and at the optimal temperature will help to keep it away. Once the infection starts, if you act quickly, you might be able to save unaffected seedlings. After transplanting your seedlings, discard all material and sanitize your trays and equipment with a 10% bleach / peroxide solution before using it again.

So you have been good at keeping your seedlings happy and healthy in their trays, but remember that this is only a temporary home for them. After about 6 weeks they should be ready to go into their permanent space. Have a look at our entry on Transplanting Seedlings to prepare yourself for the big move!

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