No spell on this plane has been able to replace manure and sunlight. However you can many things. You can try to attract certain animals to your garden to eat the pests. So perhaps an attraction spell or grow plants that would attract said garden helper. Try putting a ornament in the garden to attract said helper. So maybe a tribute to a snake or to birds. Just focus the energy and the desire to having the pests removed.
You could try putting crystals in your garden full of positive energy to enrich the garden.
A blessing is a desire for positive will. If you want to bless the garden take pride in it. Be positive and relaxed in it. That is not only respecting it but if it is doing that for you then it is a blessing. Your respect earns its blessing. What you give comes back.
Now you can always try those stupid sprays to get rid of pests. A bug zapper is also a possibility. I would go for the natural approach and gain nature's assistance. Perhaps even a bat house (they are known to eat fruit too so beware, but they also will get rid of your mosquitoes)
Now if you want the magick approach you put a barrier over the garden. The calibration to only keep pests out would be tedious. It would also be not as natural.
There is my input, I hope it helps.
