Dracunculus vulgaris.

First part of the question: waiting for the compost delivery won't hurt the Weeping Siberian Spruce. It's got a very slow growth rate (6-10" per year) so it won't get much more potbound than it is now. Wrap the black nursery pot with something white, so the sun doesn't overheat it, and keep it well watered. You say the soil doesn't retain moisture. Does than mean it drains quickly, or that it runs off on the surface? Dig a hole and fill it half way with water. Time how long it takes to drain. If it drains quickly, then use the compost to amend the backfill, but don't include any peat moss. This tree likes moist well-drained soil. The existing soil, mixed with compost will hold enough moisture to satisfy it, and as long as it drains quickly, the tree should be happy. Since you'll be installing the tree several weeks after using the RoundUp, it won't be a concern. It'll all be gone (probably already is).

If you live somewhere with freaky weather it is always best to sow a few seeds and then sow some two weeks to one month later to act as back up plants should the first batch not survive. Its all about timing. If they stay in their pots too long, some plants just never do as well in the garden as those that got outside and in the ground at the perfect time. You'll never be able to forecast that "perfect" time so just take the risks you're comfortable with. Hot weather lovers like morning glories and zinnias do not do any better starting them early. They just kinda sit still until things warm up so there isn't a huge advantage to starting them early. They will set seed which will over winter and sprout next year but the zinnia seedlings won't show up until summer is half over and the morning glories will show up where you don't want them and also a bit late. Two things will slow down seedlings - lack of sunlight (much stronger than indoor lighting) and lack of warmth. It is better the keep them starved for light while you wait for things to warm up outside. Cool temps bring with them all sorts of rot problems with seedlings. If you're starting large seeds of things like melons or cucumbers just stick two or three seeds in each space and then use scissors to chop off the heads of the weakest plants after they're a week or so old. No need to risk damaging roots by digging them up to thin them. The headless ones will sink back into the soil over time. The truth about roots - the roots you see when you dig up a plant are not the parts of the roots that do the actual work of drawing in water and nutrients from the soil. The real workers as far as roots go are microscopic. Only superman can see them with the naked eye (and he ain't much of a gardener!). You can gauge a plants health by looking at its roots but the damage that is done by handling baby plants is to the microscopic roots. Some plants just freak out when those roots are damaged.

You don't really need a meter to check the moisture in your soil. Push your finger down in the soil to see if it is moist down an inch or two. If it is then you don't need to water. If it is really soggy and wet instead of only moist, you have too much water which is usually a result of blocked or missing drain holes or poor potting mix. If it is dry it is past time to water. If you prefer to use a meter, you can check it against your "calibrated" finger and see what reading indicates water is needed. Guess it saves a dirty finger, but I like the hands on method myself. Small pots with several plants may need water a few times a day. Watch the plants and you can begin to see if they are wilting slightly. If they are it is just a bit past time to add water. If the pots have the correct potting mix and drain well you can add alot of water without worrying. The excess will drain out the holes. The planters should have potting MIX, not a bagged topsoil or soil dug up from the yard. The potting mix drains well and has air spaces that the roots need. Many of the mixes contain lots of peat and maybe some vermiculite or perlite. Most garden centers and even Target and Walmart carry suitable mixes. Miracle Gro Potting Mix is readily available but many others are as good or better. Do your pots have drain holes? If excess water cannot drain out your plants will suffer. If the holes are only on the bottom and your plants set on a flat surface they may not drain well either. If you can set them on an unueven surface or put a few sticks or stones under them, it will leave the holes open to drain. How many plants are in the pot you seeded? If the plants are too crowded they may use water so quickly that you can not keep them wet enough. Did the soil get very dry? Did the plants get real droppy? That could easily turn them dry and crispy. Sometimes they are done for then. Other times the center stem is okay and may regrow leaves from the leaf nodes. How big are your pots? Even if you water several times a day, small pots may not work well. I like to have everything in pots that are at least 10 inches across. And larger ones are even better. Your plants need light to grow, but they can come inside for awhile during heavy rain, high winds, and low temps (below 45 F.) Sometimes mine would be better inside but I'm to lazy to bring them all in :) If you can stand the heat inside your place with no AC, then your plants should be okay also. However, if you keep them in alot they will adjust to the conditions there and may get sun or wind burn when put back outside. If they are outside most of the time they get tougher and will be stronger plants. Container plants need to be fertilized. Follow label directions and don't overdo it. Too much fertilizer is worse than too little. Again, most garden centers carry a fertilizer for houseplants. Some are powders that you mix up, mine is 1/2 teas. per gallon of water. Some are spikes you stick in the pot and they fertilize for several weeks or months. What kind of plants do you have? Some do best in full sun and love the heat. Others do better in shade and don't handle high temps as well. You may need to experiment a bit to find the right ones for your area. I hope your plants are doing well. Flowers will improve the looks of most any home. Ask around and you may find another plant lover in the area who can give you advice for the local weather conditions. Otherwise keep trying. You can learn alot by watching the plants closely and seeing how they respond to various conditions. You may lose a few, but you will do better the next time.