You should never feel bad about buying nursery plants. Sometimes it just makes sense to buy them, especially if you are unfamiliar with that particular plant. However, growing your own does have a slight advantage. You can have more variety in your garden, and when you seed your plants yourself, you get a jump on the growing season.
But when you reach this point, you may still be overwhelmed by all the other work you have done to get this greenhouse ready. It’s a new environment, and you want to make sure that everything is done the best you can.
You are probably wondering when you can start growing. Different plants are going to have their optimal planting dates, and this depends on where you live and what zone your greenhouse is going to be in. Some seeds don’t really respond to an early start, so they will grow in your greenhouse as they would outside.
When you look at your zones, you can also find your planting calendar. This is a helpful way to see when you can start growing in your specific zone. In short, the best times to plant your spring and summer plants will be in January or February, and your winter plants will be planted from August to October. Again, check your zones so you can work efficiently.
Your Needed Supplies for Starting Seeds
Seeds
You have to choose what you want to grow for the season. The first thing you should think about are the fruits and vegetables you actually like and the ornamentals that sound appealing.
After that, you need to look at the plant descriptions. You want to know which seeds are going to grow best in your zone, so turn to your zone map. Seed packets will also have a helpful guide on the back that will let you know where they grow best.
You can buy seeds from your garden center, nursery, or any local retailer, but the seeds won’t be as diverse. That is why ordering from a specialty retailer might be a better route. They often sell seed varieties that are organic and are better suited to meet the special needs of your greenhouse and your zone.
Starting Pots and Trays
Some plants will start better in seed trays, and after a few growing seasons, you will develop a preference for type and size. However, you should always aim for trays that will sit in another tray that will catch water runoff. You also want domed lids, whether they come with the tray or you have to buy your own. These lids will keep moisture and warmth in, which will help a lot when starting your growing seasons early and trying to assist germination.
Other seeds are going to be better started in pots, which means you are going to need various types and sizes depending on what you’re growing. You’ll typically start with nursery mini pots. They take up more space than seedling trays, but they are better fit for starting seeds of larger plants. Below, we will discuss different types of pots and trays.
- Seedling 6-packs:
These containers will have six individual cells for starting seeds. You can go for the smaller 1.5″ square. These are good for flowers, greens, herbs, and plants that you are going to pot or transplant quickly after they sprout.
You will have plants that need more space for roots because they need a longer growth period at this stage. For example, broccoli would be a plant that needs a larger tray that will have large-cell 6-packs.
- Nursery mini pots:
Your larger plants will likely do better in a 4″ or 6″ container. While they are not space friendly, you want to think about the plant’s needs first.
There is more soil space in pots that means you are going to hold on to more moisture. It cuts down on how often you will water while keeping the seedlings from drying out. More space also means more root space. Some plants are going to get big quickly, so they are going to be root- bound just as fast.
Having them in bigger containers means you don’t have to rush to get them into a new pot, which can be a hassle when potting plants.
- Biodegradable seedling cups:
You will see these when you’re getting trays and pots. First off, they will be single-use products, so you will buy them each growing season.
While these “plantable” containers may seem like a straightforward route, there are drawbacks. Sometimes the cup doesn’t fully break down and will hinder the root system from growing. That will ultimately affect your plant in the long run.
On the other hand, some people will use something like a toilet paper roll to make a cup to make sure it breaks down. It does work, but you also risk them breaking down too early, which can damage the seedling.
- Reusing your seedling pots and trays:
Having trays and pots that you can use for several growing seasons will save you a lot of money in the end. You just need to remember to clean and disinfect them when you’re cleaning your greenhouse.
Seed-Starting Soil or Medium
Your seeds need to be started in a fresh seedling starting mix. You don’t want to use potting soil or mixes from your raised beds. These aren’t poor soils, but they are often too dense and heavy to allow good germination. You don’t want to stunt the growth of the fine roots or place seedlings in something that won’t keep moisture. You also want to avoid using other soils anyway, as they may have pests or diseases that seedlings can’t handle.
Whatever you do, don’t use any fertilizer in your seed-starting soil. This can burn seeds and seedlings, which will slow their growth or kill them. You can find recipes for seedling mix but finding a bagged mix will be more than fine. If you want to add some more punch to the mix, you can mix in worm castings and the tiniest amount of potting soil.
Sowing Your Seeds
With the previous things and all the work you have done to give your greenhouse what it needs to create the ideal climate, now it’s time to get your seeds into their trays.
Step 1: Get Your Labels Ready
Once you know what you’re growing, you should spend some time before planting to write all of your labels out.
Trying to label your plants while planting can get confusing, especially when planting a lot of seeds at once. Doing this means you can put the label on, sow the seed, and it is done.
Step 2: Prepare Your Seedling Mix
You want to get a large tub to make a seedling mix. This mixture is going to be a 70-20-10 combination.
Your majority (70%) is going to be the bagged seedling soil. Twenty percent of this mix will be organic potting soil or finished compost, and you will finish this off with worm castings. So why do you need to start this in a large tub? You will find the answer in the following steps.
Step 3: Pre-water Your Mix
You want to sow your seeds in damp soil, so you will add some water and mix until you get something that feels like a damp sponge. Some gardeners forget this step, and while it will not hurt, it is still a good idea to dampen the soil. So what benefits will you get from this step?
- It cuts out the need for heavy watering after you plant your seeds. When you heavily water a freshly planted seed, you can move it from the spot you planted it. They can either be pushed too deep or they can float up to the surface.
- Dampening your soil will aid in water absorption. Sometimes there will be dry spots, and this can repel water instead.
- While you don’t want extremely dense soil, you also don’t want something that is going to shrink after the first watering. This is what will happen if your seedling mix is dry, which will affect the amount of soil in which the roots can grow. So since you can’t add more soil on top of that, it’s best to remember to pre-moisten before sowing.
Step 4: Fill Your Containers With Mix
This is another reason why you want to work with a large tub. When you put your soil in your trays and pots, you will do this right over the tub, which keeps the amount of mess you make way down.
Using one of your scoops, fill the containers. You might be tempted but do not compact that soil. Give it a shake or tap to make sure your trays or pots are filled. This will help you avoid leaving any voids in the containers.
Step 5: Sow the Seeds
Seed packets are going to give you everything you need to know. They will tell you the best time to plant indoors and outdoors. They can tell you the ideal soil temperature for the seed to germinate, when and how to fertilize the plant, and other tips. Seed packets are also going to tell you how deep to plant your seed.
They will also tell you how many seeds you can plant in a given space. You never want to plant over five seeds, but you also never want to plant just one seed, either. If you overseed, the seedlings will start running into issues when they get bigger. If you only plant one, you risk that seed not germinating. That would be a waste of time and a container. There are a couple of helpful tips for you to know just how many seeds you should sow:
- Germination rate: Another helpful listing on a seed packet is the germination rate, which will tell you how a particular batch of seeds did during tests. For example, seeing 90% would mean that 90% of the seeds germinated during tests. If you have a high percentage, then you can plant two seeds per container. However, if you see a low germination percentage, then you will want to plant more (four to five seeds per container). You will also want to up the number you plant if you are using old seeds.
- Size and amount per packet: Some of your seeds are going to be quite large, and there will only be a few in a packet. If their germination rate is decently high, you should only sow two seeds. There are also very tiny seeds, and there is a seemingly infinite amount in a pack. With them, it’s not worth the trouble to pick one individual seed, so just take a small pinch to plant.
Seeds are cheap, and you get a lot in your packets, so if you have some extra trays and pots, you can plant a few for backup. This will give you a safety net if some seeds don’t see germination or die later on. If you don’t have the space for your extra ones, you can move them outside and let them grow. You could also give them to someone else for their garden.
You might have remembered something from earlier on regarding presoaking seeds before planting. There are seeds that have a harder shell, and presoaking will help them break out quicker. While this is helpful for some, don’t worry if you miss this step.
After you know how deep your seeds need to go, use your finger or a small tool to make a hole in the soil’s top. Then drop your seeds in that hole and cover them. Remember to not pack them down. If you have seeds that just need to be spread on the soil, it can still be helpful to sprinkle a bit of soil on top to keep them from drying out. Just make sure you aren’t putting in too much.
Step 6: Water
If you have planted in damp soil, this step is very easy. You don’t want to drown your seeds, but you also don’t want them to dry out while they are germinating. A light misting over the top with a spray bottle is all you need. Try to avoid using your watering cans or other methods at this stage.
Step 7: Cover Your Trays
You want to keep your trays covered until your plants have sprouted. This keeps your soil and seeds moist and warm. You can use humidity domes, which will usually come with your trays. You can also use plastic lids from baking dishes or even plastic wrap if you are in a pinch, as long as it’s clear.
Step 8: Keep Them Warm
You want the soil temperatures to be between 70 and 80 °F, so make sure your greenhouse is getting the job done. Heating mats, greenhouse heaters, and plenty of sun will be perfect for your seeds and seedlings.
