“Pretty much everything you grow in the garden is going to need fertilizer at some point,” says Emma Erler, Homegrown NH host and lead horticulturist at Kirkwood Gardens at Squam Lakes Natural Science Center.
If you're a vegetable gardener and you tend to add compost every year, such as composted manure, you may not need to add a lot of nutrients to your garden, because those nutrients are already there in that organic material.
But if you have a lawn or a garden that hasn't had any amendments added to it recently, chances are those plants could use a boost from some fertilizer.
A fertilizer can be organic or inorganic; this refers to the source of those nutrients. This difference has some impacts on how these fertilizers are used in the garden.
With organic fertilizers, such as poultry manures or compost, you typically get plant or animal-based nutrients that aren’t broken down yet into a form that plants can use. Organic fertilizers release nutrients slowly as they decompose, improving soil structure and creating beneficial microbial activity.
“I find that organic fertilizers are my preference when I'm gardening in the soil,” says Erler, ”because you need microorganisms provided by the soil for organic fertilizers to be released so that the plants can access those nutrients.”
An inorganic fertilizer is made up of synthetic substances containing concentrated plant nutrients like nitrogen, phosphorus, and potassium. The nutrients have been derived into a form that plants can use immediately.
“If I'm planting in a container and I’m using a potting mix, it probably doesn't have a whole lot of fungi or bacteria in it to unlock the nutrients, so I'm going to use an inorganic fertilizer,” says Erler.
For vegetables, the balance is making sure the plants have enough nutrients to grow healthy leaves and shoots, but not so much that it slows down fruit production.
“Sometimes with those tomatoes, with those peppers, we give the plants too much nitrogen, and then they just go gangbusters, growing leaves and shoots,” says Erler, “but we don't see any flowers or fruit.”
If you're growing tomatoes, it's possible to buy a tomato fertilizer that has those nutrients at the right ratios to grow tomatoes without having to worry too much about over-fertilizing.
“Look at the package instructions. That's going to tell you how much to apply and help you decide if you're over-fertilizing or under-fertilizing as well as the timing,” says Erler.
“I like to fertilize when plants are not too stressed, so if we've had a drought, if it's really dry, I hold off on fertilizing when plants seem healthy,” she says.
“If we’ve had some nice rainfall or I've been really good with my irrigating, that's when I go about fertilizing annuals and vegetables. In terms of perennials, you can really do that at any point during the growing season.”
See you in the garden!
Homegrown NH is a collaboration between Squam Lakes Natural Science Center and NHPR.
