Giving your plants a strong, head start is very important for successful indoor gardening. If your seedlings are weak and spindly, they may not make it off the propagation bench. Even if they do survive, they may never reach their true genetic potential. So following a few propagation basics is well worth the time and effort.
Seed Soaks
Whenever possible, it’s best to use fresh seeds that have been stored in a cool, dark place. Fresh seeds are loaded with starches and stored nutrients, and they typically have a good germination rate when given adequate moisture and warmth. But if you have older seeds or seeds that haven’t been stored under ideal conditions, a few extra precautions should be taken. Kelp extracts make a great seed soak for older seeds. Kelp is loaded with natural growth hormones, and it contains many beneficial trace elements. One of the hormones in seaweed extracts is called gibberilic acid. In nature, gibberilic acid triggers the release of enzymes in the seeds that begin the germination process. Soaking seeds over night in seaweed extracts may improve germination rates by up to 30%, especially in marginal seeds.
In hydroponic applications, rockwool starter cubes are a good choice for starting seeds. A sheet of rockwool starter cubes fits perfectly in a standard nursery tray, and it has the perfect air to water-holding capacity. Just make sure that you condition the rockwool with pH adjusted water before planting. For best results, soak the rockwool starter cubes for a few minutes in water with a pH of about 5.5. The conditioning solution will neutralize the limestone dust left over from the manufacturing process and provide plenty of moisture for germinating seeds. Just make sure that you pour off the excess water so that the rockwool isn’t sitting in a puddle of water. Then simply plant one seed in each starter cube.
Full-Spectrum Lights
It’s also a good idea to cover the propagation tray with a humidity dome and place the tray under full-spectrum lights. The dome will keep the relative humidity in the propagation tray at about 98%, ideal for germinating seeds, and the full-spectrum lights will help keep the seedlings from stretching once they germinate. Seedlings don’t need much light intensity. Two standard fluorescent lamps over a nursery tray are adequate, but many gardeners (including myself) prefer four lamps. Full-spectrum fluorescent grow lamps work best. The blue end of the spectrum helps seedlings remain short and stocky, and the red end of the spectrum helps stimulate root growth. Just keep the lamps a few inches above the growing tips and raise the lamps as needed. Also, make sure that you remove the humidity dome after all of the seeds have germinated and started to grow. Keeping the humidity dome on too long can set up an environment for fungal pathogens.
Bottom Heat
Bottom heat is also beneficial, especial for germinating tropical seeds. Most heating mats are set at the factory to provide a temperature of 78 degrees F. The warm temperature helps activate enzymes such as amylase, the enzyme that breaks down starches into sugars. The high-energy sugars provide energy for cell division and growth. Just remember not to use bottom heat when germinating cool weather crops such as lettuce and spinach. Warm temperatures actually inhibit germination in cool-weather crops! Check your seed packages for any other special considerations. For example, some seeds may need to be cold treated before they can germinate, and a few native seeds need to be scratched or treated with acids before they can germinate. Fortunately, most garden variety seeds are easy to germinate with very little special treatment.
After the seeds germinate, the bottom heat should be reduced or removed. The warmer the water temperature, the less dissolved oxygen the water can hold. Remember, it’s not overwatering that kills the plant, its lack of oxygen! If the water temperature exceeds 78 degrees, it can’t hold enough dissolved oxygen and it sets up an environment for anaerobic fungi. Anaerobic fungi grow in stagnant water, without oxygen, and they are the bad guys that cause root rot. So after the seeds germinate, try to maintain the water temperature between 68 and 75 degrees for best results.
Starter Fertilizers
Seeds contain all of the minerals and nutrients necessary to germinate and start to grow, so they can be germinated with water only. Once the first true leaves start to appear, however, they need a starter fertilizer. The first leaves that pop out of the seed are not “true” leaves; they are the embryonic leaves that are formed inside the seed. The second sets of leaves are the plant’s first true leaves. When they appear it is a good sign that the seedling is actively growing and that it is ready for a mild fertilizer.
During the first few weeks use a full-spectrum fertilizer, including trace elements such as iron, copper, manganese and zinc. The trace metals are cofactors that actually turn on enzymes used for photosynthesis and cellular metabolism. Also, make sure the pH is kept in the slightly acidic range, somewhere between 5.8 and 6.4. If the pH rises much past 6.5, iron starts to become unavailable to the plant. Iron is a catalyst for the formation of chlorophyll, essential for photosynthesis. If the pH rises above 7.5, all of the metal catalysts start to become unavailable and can slow down new growth. Zinc, for example, activates the enzymes necessary for IAA production, the growth hormone responsible for initiating root production.
Adequate phosphorous is also important for faster root strike and better establishment of the plant. Phosphorous is the “energy” element. It energizes the rooting process, and extra phosphorous is included in most commercial starter fertilizers. With just a little extra phosphorous, it is possible to see as much as 20% more roots at transplant!
Root Stimulants
Starter fertilizers provide all of the essential minerals that seedlings need, but organic biostimulants aid with the uptake of minerals. For example, humic and fulvic acids aid with the uptake of iron and other trace minerals. Humic acid is an intermediate chelator. “Chela” means “claw”, so humic acid molecules attach to mineral ions like a claw, holding them tightly enough to keep them from getting locked up in the soil, but loosely enough to release them to the root hairs on demand. Humic and fulvic acids also help to neutralize pH. In nature, humic acids raise the pH of acid soils and lower the pH of alkaline soils.
For even better results, combine humic acid with seaweed extracts. When used together in a 5:2 ratio, humic acid and seaweed work 50% better than either product alone! The combination stimulates root development, producing more lateral root growth and more root mass. Seaweed extracts also contain B-vitamins and amino acids that stimulate cellular metabolism and further aid with the uptake of minerals. For example, some amino acids stimulate root cells to open up calcium ion channels, allowing calcium ions to be taken up thousands of times faster than simple osmosis. Calcium helps seedlings develop thicker stems and stronger cell walls. Plus, calcium activates the enzymes that pump the growth hormones to the growing tips!
Microbial Inoculants
Treating seedlings with microbial inoculants is also a good idea. Plant-growth-promoting rhizobacteria are the biostimulant factories. Some microbes fix nitrogen from the air and feed it to the plant; others solubilze phosphorus, and others produce plant protection agents and rooting hormones. For example, some microorganisms produce the amino acid tryptophan on the surface of the roots. The root cells easily absorb the tryptophan and transport it to the leaves. The leaves then change the tryptophan into a powerful growth hormone called indole acidic acid (IAA), and the IAA is pumped to the roots to stimulate the growth of new root hairs.
Beneficial microbes also produce siderophores. The word siderophore literally means “iron carrier”. It is one of the strongest chelators of iron in nature, and it acts indirectly as a plant protection agent. As beneficial bacteria colonize the root surface, their siderophores sequester iron and make it unavailable to foreign invaders. So the roots are protected from root pathogens such as pythium and rhizoctonia. Some soiless mixes take advantage of the process by adding certain species of bacillus subtilis to the blend and calling it a “biofungicide”. But more on microbes later!
Propagation is easy if you have the right tools and follow a few simple instructions. Just give the seeds a good soaking, and provide adequate light and warmth. Afterwards, it only takes a little coaxing to grow strong, healthy seedlings with thick stems and dark green foliage. Propagation is the least expensive part of indoor growing, so don’t be afraid to throw in a few extra seeds, and always select the best of the best!
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