Once you have read your seed packet, sown your seeds, and waited, your seedlings will begin to germinate and send up their embrionic leaves. These are called cotyledons. This comes from the Greek word "kotyledon", literally translated: "cup" or "hollow". The cotyledons will not usually resemble the leaf shape you may be familiar with for your specific plant. This is normal. A short time later you will see what are usually referred to as the first "true leaves". Once you see your first true leaves, and your plant is a couple of inches high, it's time to start giving them a little bit of diluted quick-release plant food. We'll talk about the types of plant food more in the next sections, but now it's time to learn the other methods of propogation every skilled gardener should know.
(...To be continued)
The most important thing to know when considering nutrients is how the main two types actually work. The first type is known as quick-release, or water soluble inorganic plant food. If you read the word "inorganic" in that last sentence and shuddered a little bit, let me explain before you rush to judgement. Inorganic doesn't mean dangerous in this context. In this case inorganic simply means the nutrients we're adding are in their purest forms, and are readily available for your plants to drink and use immediately. These types of food come in a powder or crystaline form which we will dissolve into water, pour onto soil (or into the watering tray), and allow your plants to use right away. This food is made of macro and micro nutrients which your plants will need to grow. The three numbers you see on plant foods, labelled likeso: 5-5-5, or 3-5-10, etc, are there to tell you what ratio of macronutrients you can expect in them. These macronutrients are Nitrogen (N), Phosphorus (P), and Potassium (K). Micronutrients are too many to list here (calcium, magneseum and many others), but are less important for the beginning stage of your plant's vegetative growth, so we'll cover them later on. The second type of nutrients come in the form of slow-release organic fertilizers. These fertilizers come from mixtures of things like animal manure, and composted plant material. This type of food releases slowly because it takes time for the living organisms in soil to eat them, which will then create food which is bioavalable to your plants. This is why quick-release foods are so important, especially early on in your plant's life. Instead of waiting for two weeks or more for an organic plant food to innoculate your soil with life, feed that life, then feed your plants, you can simply add water-soluble quick-release food and feed the plants directly, and immediately.
Soon after adding your nutrients, you will see your seedlings begin to vegetate. Vegetation is the phase of growth where your plants take on the most growth. The stalk will grow thick and tall, branches will form plentifully, and lots of leaves will develop during this stage. A healthy stalk is crucial to growing your plants to thier fullest potential. This is because the stalk facilitates the transportation of food from the roots to the rest of the plant, and because it will allow the plant to develop the biggest flowers (and fruit, if aplicable) once your plant enters its later stages.
You should check on your seedlings intermittently during the beginning of vegetation to see if it's time to up-pot, or to transplant the seedlings into the ground. Do this by picking up the container, and looking at the drainage holes for roots. If you see roots trying to get out through the holes, it may be time to up-pot. If the time has come to give your plant more room, grab the next container, and add your primary soil mix to the container, being sure to leave some room to add your seedlings without making a mess. If you're planning on going from starter tray directly to the ground or garden bed at this stage, now is the time to do so. Your primary mix can be just like your starter mix if that's what your plants like, or it may contain more compost and chunks of uncomposted organic matter such as pine bark mini nuggets if your plant can handle this. Do your reading on the species before you commit to this choice. Most endemic species will happily grow in your area's soil at this point, so this advice is more focused on those of you using garden beds or pots, and those who want to give their plants a bit more time to vegetate in a controlled environment before setting them into the native soil.
To up-pot, take your starter trays, separate them into their 6-cell sections, and carefully take them to your prepared larger pots, or garden bed. Prepare the holes ahead of time by getting your container close to full, leaving room to add some soil. Make your holes equal depth to your plugs, and ~twice as wide. Carefully support your seedlings using your fingers while inverting the 6-cells so the "plugs" don't fall out. Plugs are your seedlings inside of their cells. Gently massage the individual cell using your second hand, or have someone help you if you don't have a second hand. Now tap on the bottom of the cell while inverted, and slowly bring down the fingers holding that plug in place, your plug should come out easily at this point into your fingers, which should be placed on either side of the seedling's stem. Remove the plug, support the root ball gently, set down your 6-cell right side up, and place your plug into the soil. If the top of your plug's soil sticks up more than ~1/4" above the top of the soil level around it, either add soul to get it level if there is room to do so, or gently pick the plug back up from the root ball, and dig a slightly deeper hole before replacing the plug into the soil.
You've taken the first steps to growing wild. You identified and collected a handful of pretty plants, you potted (or better yet planted into the ground) your starters, you watched a hundred hours of videos, and you found yourself asking 'Now what?'. Now you share. Share what you've learned with fellow newbies, share your excess plants which are beginning to spread by themselves, share your time helping a neighbor or acquantance getting their garden started, or restarted. The true value of connecting with nature is beginning to understand and appreciate your own humanity. You are a native species too, and you belong to a community even though it may not feel that way sometimes. Sign up for some forums, post on a bulletin board at a park, do anything to reach out to your fellow gardener and start making connections. These relationships will grow increasingly valuable during your journey in botany. Speaking of which, learn the ropes of botany proper. Start familiarizing yourself with the plants you are growing in a more academic capacity. You don't need to go to school to do this, just go online and search for "entymology", and start reading and watching content created by the "real botanists". You are today's link in a chain which spans the aeons of Earth's history, and botany is a valuable window into that inconceivably long past. I firmly believe that learning about botany can make you a kinder, more humble human being if you let it. These 'weeds' are tools which can take you to places you've never experienced, and no, you don't need to make medicine out of them (if that's your thing, no judement) to expand your mind. Whatever you decide to do next, just keep growing. You will thank yourself later.